WO2001037383A2

WO2001037383A2 - Group iii-nitride semiconductor structures with reduced phase separation

Info

Publication number: WO2001037383A2
Application number: PCT/IB2000/001681
Authority: WO
Inventors: Toru Takayama; Baba Takaaki; S. Harris James, Jr.
Original assignee: Matsushita Electric Industrial Co. Ltd.
Priority date: 1999-11-16
Filing date: 2000-11-15
Publication date: 2001-05-25
Also published as: JP4837012B2; WO2001037383A3; JP2009049422A; JP2003514402A

Abstract

Group III-nitride quaternary and pentenary material systems and methods are disclosed for use in semiconductor structures, including laser diodes, transistors, and photodetectors, which reduce or eliminate phase separation and provide increased emission efficiency. In an exemplary embodiment the semiconductor structure includes a first ternary, quaternary or pentenary material layer using BlnGaAlN material system of a first conduction type formed substantially without phase separation, and a quaternary or pentenary material active layer using BlnGaAlN material system substantially without phase separation, and a third ternary, quaternary or pentenary material layer using BlnGaAlN material system of an opposite conduction type formed substantially without phase separation.

Description

SEMICONDUCTOR STRUCTURES USING A GROUP HI-NITRIDE MATERIAL SYSTEM WITH REDUCED PHASE SEPARATION AND METHOD OF FABRICATION

SPECIFICATION

RELATED CASES

This application is a continuation in part of U.S. Patent Applications S.N.09/276,886 filed 3/26/99, entitled "Semiconductor Structures Using A Group Ill-Nitride Quaternary Material System with Reduced Phase Separation and Method of Fabrication" and S.N. 09/365,105 filed 7/30/99, entitled "Semiconductor Structures Using A Group Ill-Nitride Quaternary Material System with Reduced Phase Separation and Method of Fabrication".

FIELD OF THE INVENTION

This application relates to semiconductor structures and processes, and particularly relates to group Ill-nitride materials systems and methods such as might be used in laser diodes.

BACKGROUND OF THE INVENTION

The development of the blue laser light source has heralded the next generation of high density optical devices, including disc memories, DVDs, and so on. Figure 1 shows a cross sectional illustration of a prior art semiconductor laser device. (S. Nakamura, MRS BULLETIN, Vol. 23, No. 5, pp. 37-43, 1998.) On a sapphire substrate 5, a gallium nitride (GaN) buffer layer 10 is formed, followed by an n-type GaN layer 15, and a 0.1 μm thick silicon dioxide (SiO₂) layer 20 which is 5 patterned to form 4 μ m wide stripe windows 25 with a periodicity of 12 μm in the GaN<1 -100> direction. Thereafter, an n-type GaN layer 30, an n-type indium gallium nitride (ln_{0 1}Ga₀₉N) layer 35, an n-type aluminum gallium nitride (AI_{0 14}Ga₀₈₆ N)/GaN MD-SLS (Modulation Doped Strained-Layer Superlattices) cladding layer 40, and an n-type GaN cladding layer 45 are formed. Next, an ln₀₀₂Ga₀₉₈N/ln_{0 15}Ga₀₈₅N MQW 10 (Multiple Quantum Well) active layer 50 is formed followed by a p-type AI₀₂Ga₀₈N cladding layer 55, a p-type GaN cladding layer 60, a p-type Al_0., ₄ Ga₀₈₆N/GaN MD- SLS cladding layer 65, and a p-type GaN cladding layer 70. A ridge stripe structure is formed in the p-type Al₀., ₄Ga₀₈₆N/GaN MD-SLS cladding layer 55 to confine the optical field which propagates in the ridge waveguide structure in the lateral direction. 15 Electrodes are formed on the p-type GaN cladding layer 70 and n-type GaN cladding layer 30 to provide current injection.

In the structure shown in Figure 1, the n-type GaN cladding layer 45 and the p-type GaN 60 cladding layer are light-guiding layers. The n-type Al_{0 1 4}Ga₀₈₆N/GaN MD-SLS cladding layer 40 and the p-type Al₀₁₄Ga₀₈₆N/GaN MD-SLS cladding layer 20 65 act as cladding layers for confinement of the carriers and the light emitted from the active region of the InGaN MQW layer 50. The n-type ln _ιGa_0.9N layer 35 serves as a buffer layer for the thick AIGaN film growth to prevent cracking.

By using the structure shown in Figure 1 , carriers are injected into the InGaN

MQW active layer 50 through the electrodes, leading to emission of light in the

25 wavelength region of 400 nm. The optical field is confined in the active layer in the lateral direction due to the ridge waveguide structure formed in the p-type Al_{0 4}

Ga₀₈₆N/GaN MD-SLS cladding layer 65 because the effective refractive index under the ridge stripe region is larger than that outside the ridge stripe region. On the other hand, the optical field is confined in the active layer in the transverse direction by the 0 n-type GaN cladding layer 45, the n-type Al_{0 14}Ga₀₈₆N/GaN MD-SLS cladding layers

40, the p-type GaN cladding layer 60, and the p-type Al_{0 14}Ga₀₈₆N/GaN MD-SLS cladding layer 55 because the refractive index of the of the active layer is larger than that of the n-type GaN cladding layer 45 and the p-type GaN cladding layer 60, the n-type AI_{0 14}Ga₀₈₆N/GaN MD-SLS layer 40, and the p-type AI_{0 14}Ga₀₈₆N/GaN MD-SLS 5 cladding layer 60. Therefore, fundamental transverse mode operation is obtained.

However, for the structure shown in Figure 1 , it is difficult to reduce the defect density to the order of less than 10⁸ cm^"2, because the lattice constants of AIGaN,

InGaN, and GaN _. differ sufficiently different from each other that defects are generated in the structure as a way to release the strain energy whenever the total thickness of the n-type ln₀ ^Ga^N layer 35, the ln₀₀₂Ga₀₉₈N/ln_{0 15}Ga₀₈₅N MQW active layer 50, the n-type AI_{0 14}Ga₀₈₆N/GaN MD-SLS cladding layer 40, the p-type Al_{0 14}Ga₀₈₆N/GaN MD-SLS cladding layer 65, and the p-type AI₀₂Ga₀₈N cladding layer 55 exceeds the critical thickness. The defects result from phase separation and act as absorption centers for the lasing light, causing decreased light emission efficiency and increased threshold current. The result is that the operating current becomes large, which in turn causes reliability to suffer.

Moreover, the ternary alloy system of InGaN is used as an active layer in the structure shown in Figure 1. In this case, the band gap energy changes from 1.9 eV for InN to 3.5 eV for GaN. Therefore, ultraviolet light which has an energy level higher than 3.5 eV cannot be obtained by using an InGaN active layer. This presents difficulties, since ultraviolet light is attractive as a light source for the optical pick up device in, for example, higher density optical disc memory systems and other devices.

To better understand the defects which result from phase separation in conventional ternary materials systems, the mismatch of lattice constants between InN, GaN, and AIN must be understood. The lattice mismatch between InN and GaN, between InN and AIN, and between GaN and AIN, are 11.3%, 13.9%, and 2.3%, respectively. Therefore, an internal strain energy accumulates in an InGaAIN layer, even if the equivalent lattice constant is the same as that of the substrate due to the fact that equivalent bond lengths are different from each other between InN, GaN, and AIN. In order to reduce the internal strain energy, there is a compositional range which phase separates in the InGaAIN lattice mismatched material system, where In atoms, Ga atoms, and Al atoms are inhomogeneously distributed in the layer. The result of phase separation is that In atoms, Ga atoms, and Al atoms in the InGaAIN layers are not distributed uniformly according to the atomic mole fraction in each constituent layer. In turn, this means the band gap energy distribution of any layer which includes phase separation also becomes inhomogeneous. The band gap region of the phase separated portion acts disproportionately as an optical absorption center or causes optical scattering for the waveguided light. As noted above, a typical prior art solution to these problems has been to increase drive current, thus reducing the life of the semiconductor device.

As a result, there has been a long felt need for a semiconductor structure which minimizes lattice defects due to phase separation and can be used, for example, as a laser diode which emits blue or UV light at high efficiency, and for other semiconductor structures such as transistors. SUMMARY OF THE INVENTION

The present invention substantially overcomes the limitations of the prior art by providing a semiconductor structure which substantially reduces defect densities by materially reducing phase separation between the layers of the structure. This in turn permits substantially improved emission efficiency. In general, the present invention utilizes group Ill-nitride quaternary and pentenary material systems and methods.

To reduce phase separation, it has been found possible to provide a semiconductor device with InGaAIN layers having homogeneous In content, Al content, Ga content distribution in each layer. In a light emitting device, this permits optical absorption loss and waveguide scattering loss to be reduced, resulting in a high efficiency light emitting device.

A quaternary material system such as InGaAIN has been found to provide, reproducibly, sufficient homogeneity to substantially reduce phase separation where the GaN mole fraction, x, and the AIN mole fraction, y, of all the constituent layers in the semiconductor structure satisfy the condition that x + 1.2y nearly equals a constant value.

A device according to the present invention typically includes a first layer of InGaAIN material of a first conductivity, an InGaAIN active layer, and a layer of InGaAIN material of an opposite conductivity successively formed on one another. By maintaining the mole fractions essentially in accordance with the formula x + 1.2y equals a constant, for example on the order of or nearly equal to one, the lattice constants of the constituent layers remain substantially equal to each other, leading to decreased generation of defects.

In an alternative embodiment, the semiconductor structure is fabricated essentially as above, using a quaternary materials system to eliminate phase separation and promote homogeneity across the layer boundaries. Thus, as before, the first cladding layer is a first conduction type and composition of InGaAIN, the active layer is InGaAIN of a second composition, and the second cladding layer is an opposite conduction type of InGaAIN having the composition of the first layer. However, in addition, the second cladding layer has a ridge structure. As before, the optical absorption loss and waveguide scattering loss is reduced, leading to higher efficiencies, with added benefit that the optical field is able to be confined in the lateral direction in the active layer under the ridge structure. This structure also permits fundamental transverse mode operation. '

In a third embodiment of the invention, suited particularly to implementation as a laser diode, the semiconductor structure comprises a first cladding of a first conduction type of an In^^Ga^A N material, an active layer of an ln_1-x2._y2Ga_x2Al_y2N material, and a second cladding layer of an opposite conduction type of an In,.^ _y3Ga_x3Al_y3N material, each successively formed on the prior layer. In such a materials system, x1 , x2, and x3 define the GaN mole fraction and y1 , y2, and y3 define the AIN mole fraction and x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 < 1 , 0 <= x3 + y3 <=1 , 1 <= x1/0.80 + y1/0.89, 1 <= x2/0.80 + y2/0.89, 1 <= X3/0.80 + y3/0.89, Eg_lnN(1 -x1 -y 1 ) + Eg_GaNx1 + Eg_AINy 1 > Eg_lnN(1 -x2-y2) + Eg_GaNx2 + Eg_AINy2, and Eg_lnN(1-x3-y3) + Eg_GaNx3 + E_gAINy3 > Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg_A(Ny2, where Eg_lnN, Eg_GaN, and Eg_AIN are the band gap energy of InN, GaN, and AIN, respectively.

To provide a reproducible semiconductor structure according to the above materials system, an exemplary embodiment of InGaAIN layers have Ga content, x, and Al content, y, which satisfy the relationship 0 <= x + y <=1 and 1<= x/0.80 + y/0.89. As before, this materials system permits reduction of the optical absorption loss and the waveguide scattering loss, resulting in a high efficiency light emitting device. Moreover, the band gap energy of the InGaAIN of an active layer becomes smaller than that of the first cladding layer and the second cladding layer when x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= X1/0.80 + y1/0.89, 1<= x2/0.80 + y2/0.89, 1<= x3/0.80 + y3/0.89, Eg_lnN(1-x1-y1) + Eg_GaNx1 + Eg^yl > Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg_AINy2, and Eg_lnN(1- x3-y3) + Eg_GaNx3 + Eg^yS > Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg_AINy2. Under these conditions, the injected carriers are confined in the active layer. In at least some embodiments, it is preferable that the third embodiment, which can be a light emitting device, has an InGaAIN single or multiple quantum well active layer whose GaN mole fraction, xw, and AIN mole-fraction, yw, of all the constituent layers satisfy the relationship of 0 < xw + yw <1 and 1<= x/0.80 + y/0.89.

One of the benefits of the foregoing structure is to reduce the threshold current density of a laser diode. This can be achieved by use of a single or multiple quantum well structure, which reduces the density of the states of the active layer. This causes the carrier density necessary for population inversion to become smaller, leading to a reduced or low threshold current density laser diode.

It is preferred that in the third embodiment, the condition of xs + 1.2ys nearly equals to a constant value - on the order of or near one - is satisfied, wherein xs and ys are the GaN mole fraction and the AIN mole fraction, respectively in each the constituent layers. As before, this causes the lattice constants of the each constituent layers to be nearly equal to each other, which in turn substantially minimizes defects due to phase separation

In a fourth embodiment of the present invention, the semiconductor structure may comprise a first cladding layer of a first conduction type of a material In^. _y1Ga_x1Al_y1N, an In^^Ga_xjAI^N active layer, and a second cladding layer of an opposite conduction type of a material

each successively formed one upon the prior layer. In addition, the second cladding layer has a ridge structure. For the foregoing materials system, x1 , x2, and x3 define the GaN mole fraction, y1 , y2, and y3 define the AIN mole fraction, and x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1, 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= x1/0.80 + y 1/0.89, 1<= X2/0.80 + y2/0.89, 1 <= x3/0.80 + y3/0.89, Eg_lnN(1-x1-y1 ) + Eg_GaNx1 + Eg_Aι_Ny1 Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg_AINy2, and Eg_lnN(1-x3-y3) + Eg_GaNx3 + Eg^ > Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg_AINy2, where Eg_lnN, Eg_GaN, and Eg_AIN are the bandgap energy of InN, GaN, and AIN, respectively.

As with the prior embodiments, each of the InGaAIN layers have a homogeneous In content, Al content, and Ga content distribution, which can be obtained reproducibly when Ga content, x, Al content, y, of each InGaAIN layer satisfies the relationship 0 <= x + y <=1 and 1<= x/0.80 + y/0.89. The band gap energy of the InGaAIN active layer becomes smaller than that of the first cladding layer and the second cladding layer when x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1 <= x1 /0.80 + y1/0.89, 1<= X2/0.80 + y2/0.89, 1<= X3/0.80 + y3/0.89, Eg_lπN(1-x1-y1 ) + Eg_GaNx1 + Eg_AINy1 > Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg^, and Eg_lnN(1-x3-y3) + Eg_GaNx3 + Eg_AINy3

> Eg_(nN(1-x2-y2) + Eg_GaNx2 + Eg^^. Similar to the prior embodiments, the injected carriers are confined in the active layer and the optical field is confined in the lateral direction in ,the active layer under the ridge structure, producing a fundamental transverse mode operation. Also similar to the prior embodiments, the fourth embodiment typically includes an InGaAIN single or multiple quantum well active layer whose GaN mole fraction, xw, and AIN mole fraction, yw of all the constituent layers satisfy the relationship of 0 < xw + yw <1 and 1<= x/0.80 + y/0.89. Also, the condition xs +

1.2ys nearly equals to a constant value on the order of or near one is typically satisfied, where xs and ys are the GaN mole fraction and the AIN mole fraction, respectively in each constituent layer. Similar parameters apply for other substrates, such as sapphire, silicon carbide, and so on.

In the Group-Ill nitride materials, BN is also attractive for the application to visible light emitting devices, visible light detectors, and high power transistor devices because of its wide band gap and high thermal conductivity. The same structural design concepts for InGaAIN material are also can be applied to the semiconductor devices using the other material systems such as BAIGaN, BGalnN, BlnAIN.

In the case of the semiconductor device using BAIGaN material system, each of the BAIGaN layers have a homogeneous B content, Al content, and Ga content distribution, which can be obtained reproducibly when Al content, x, Ga content, y, of each BAIGaN layer satisfies the relationship 0 <= x + y <=1 and 1<= 1.04x + 1.03y. In the case of the semiconductor device using BGalnN material system, each of the BGalnN layers have a homogeneous B content, Ga content, and In content distribution, which can be obtained reproducibly when Ga content, x, In content, y, of each BGalnN layer satisfies the relationship 0 <= x + y <=1 and 1 <= 1.03x + 0.88y or 1<=0.95x + 1.01y. In the case of the semiconductor device using BlnAIN material system, each of the BlnAIN layers have a homogeneous B content, In content, and Al content distribution, which can be obtained reproducibly when In content, x, Al content, y, of each BlnAIN layer satisfies the relationship 0 <= x + y <=1 and 1 <= 1.01 x + 0.88y or 1<=0.61x + 1.04y. From the foregoing, it can be appreciated that the materials system of the present invention may be generalized with the description B₁._x._y._zln_xGa_yAl_zN, where each of x, y and z can be zero or nonzero for particular materials systems. It will be appreciated that, if one of x, y or z is zero, a quaternary materials system results. Thus, if x=0, the materials system is generally BGaAIN; if y=0, the materials system is generally BlnAIN; while if z=0, the materials system is generally BlnGaN. However, if the total of x, y and z equals one, then the materials system becomes InGaAIN. In each instance the relationship between the specific materials may vary as discussed above to avoid phase separation and follow the structural design concepts of the present invention, for example to provide an ultraviolet, blue, red or infrared laser diode or detector, or other semiconductor structure. It will also be appreciated that, if none of x, y or z is zero and they do not sum to one, a pentenary material system will result.

The foregoing results may be achieved with conventional processing temperatures and times, typically in the range of 500°C to 1000°C. See "Growth of high optical and electrical quality GaN layers using low-pressure metalorganic chemical vapor deposition," Appl. Phys. Lett. 58 (5), 4 February 1991 p. 526 et seq. The present invention may be better appreciated by the following Detailed Description of the Invention, taken together with the attached Figures.

FIGURES

Figure 1 shows a prior art laser diode structure using a conventional ternary materials system. Figure 2 shows in cross-sectional view a semiconductor structure according to a first embodiment of the invention.

Figure 3 shows a graph of the light-current characteristics of a laser diode according to the structure of Figure 1. Figure 4 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with a first embodiment of the invention.

Figure 5 shows in cross-sectional view a semiconductor structure according to a second embodiment.

Figure 6 shows a graph of the light-current characteristics of a laser diode according to the structure of Figure 4.

Figure 7 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with the first embodiment of the invention. Figure 8 is a cross-sectional illustration of a semiconductor laser diode of the third embodiment. Figure 9 shows the light-current characteristics of the laser diode of the third embodiment.

Figure 10 shows a series of the fabrication steps of a semiconductor laser diode in one exemplary example of the third embodiment.

Figure 11 is a cross-sectional illustration of a semiconductor laser diode of the fourth embodiment.

Figure 12 shows the light-current characteristics of the laser diode of the fourth embodiment.

Figure 13 shows a series of the fabrication steps of a semiconductor laser diode in one exemplary form of the fourth embodiment. Figure 14 shows in plot form the boundary between the phase separation region and the region without phase separation at various growth temperatures.

Figure 15 shows the content choice region of Ga content and Al content in InGaAIN to avoid phase separation at a growth temperature below approximately 1000 °C. Figure 16 shows the content choice line of Ga content and Al content in

InGaAIN to avoid phase separation at a growth temperature below approximately 1000 °C which, at the same time, creates a lattice constant of InGaAIN substantially equivalent to that of GaN.

Figures 17A and 17B show representations of bipolar and FET transistors constructed in accordance with the materials system of the present invention.

Figure 18 shows an implementation of the presention invention as a phototransistor.

Figure 19 shows an implementation of the present invention as a photodiode. Figure 20 shows in cross-sectional view a semiconductor structure according to a fifth embodiment of the invention.

Figure 21 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with a fifth embodiment of the invention. Figure 22 shows in cross-sectional view a semiconductor structure according to a sixth embodiment.

Figure 23 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with the ninth embodiment of the invention. Figure 24 shows in plot form the boundary between the phase separation region and the region without phase separation at various growth temperatures.

Figure 25 shows the content choice region of Ga content and Al content in BAIGaN to avoid phase separation at a growth temperature below approximately 1000 °C.

Figure 26 shows the content choice line of Ga content and Al content in BAIGaN to avoid phase separation at a growth temperature below approximately 1000 °C which, at the same time, creates a lattice constant of BAIGaN substantially equivalent to that of AIN.

Figures 27A and 27B show representations of bipolar and FET transistors constructed in accordance with the materials system of the present invention. Figure 28 shows an implementation of the presention invention as a phototransistor.

Figure 29 shows an implementation of the present invention as a photodiode.

Figure 30 shows in cross-sectional view a semiconductor structure according to a seventh embodiment of the invention. - Figure 31 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with a seventh embodiment of the invention.

Figure 32 shows in cross-sectional view a semiconductor structure according to an eighth embodiment.

Figure 33 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with the eighth embodiment of the invention. Figure 34 shows in plot form the boundary between the phase separation region and the region without phase separation at various growth temperatures.

Figure 35 shows the content choice region of Ga content and In content in BGalnN to avoid phase separation at a growth temperature below approximately 1000 °C.

Figure 36 shows the content choice line of Ga content and In content in BGalnN to avoid phase separation at a growth temperature below approximately 1000 °C which, at the same time, creates a lattice constant of BGalnN substantially equivalent to that of GaN.

Figures 37A and 37B show representations of bipolar and FET transistors constructed in accordance with the materials system of the present invention.

Figure 38 shows an implementation of the presention invention as a phototransistor.

Figure 39 shows an implementation of the present invention as a photodiode. Figure 40 shows in cross-sectional view a semiconductor structure according to a ninth embodiment of the invention.

Figure 41 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with a ninth embodiment of the invention. Figure 42 shows in cross-sectional view a semiconductor structure according to a tenth embodiment.

Figure 43 shows an exemplary series of the fabrication steps for a semiconductor structure in accordance with the tenth embodiment of the invention. Figure 44 shows in plot form the boundary between the phase separation region and the region without phase separation at various growth temperatures.

Figure 45 shows the content choice region of In content and Al content in BlnAIN to avoid phase separation at a growth temperature below approximately 1000°C. Figure 46 shows the content choice line of In content and Ga content in

BlnAIN to avoid phase separation at a growth temperature below approximately 1000°C which, at the same time, creates a lattice constant of BGalnN substantially equivalent to that of AIN.

Figures 47A and 47B show representations of bipolar and FET transistors constructed in accordance with the materials system of the present invention.

Figure 48 shows an implementation of the presention invention as a phototransistor.

Figure 49 shows an implementation of the present invention as a photodiode.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to methods for constructing and semiconductor structures constructed from a family of materials systems which may be generally described by the formula B __x__y__z\n_xGa_γA\_zb\, where each of x, y and z can be zero or non-zero for particular materials systems, or where the sum of x, y and z equals one. In a first embodiment discussed herein, which describes an InGaAIN materials system more particularly described as ln₀₀₅Ga₀₇₅AI₀₂N, it can be seen that x + y + z = 1 , thus eliminating the Boron component. In a second embodiment discussed herein, an ln₀₀₁Ga₀₉₆AI₀₀₃N material is used; it can again be seen that x + y + z = 1. A third embodiment uses cladding layers of ln_{0 15}Ga₀₇₀Al_{0 15}N material together with ln_{0 15}Ga₀₈₄AI₀₀₁N material and ln_{0 16}Ga₀₈₀Al₀₀₄N material for the quantum well barrier layers. Again, both materials can be seen to comply with the equation x + y + z =1.

A fifth embodiment described hereinafter uses the material system B₀₀₁ Al₀₉₅Ga₀ ^N with AIN cladding material, while a sixth embodiment uses B₀₀₁AI₀₉₅Ga₀₀₄N material for the cladding layers together with multiple quantum well layers of B₀₀₄AI₀₆₃Ga₀₃₃N material and B₀₀₃AI₀₇₀Ga₀₂₇N. Each of these can be seen to have x = 0 in the generalized formulation.

Similarly, a seventh embodiment employs cladding layers of a Bo_.o₃Ga₀₉₆ln₀₀₁N material together with quantum well layers of a B₀₀₁Ga₀₈₆ln_{0 13}N material and a B₀₀₁Ga₀₉₀ln₀₀₉N material. An eighth embodiment employs a B₀.o₃Ga_a96ln₀₀₁N material for the cladding layers together with quantum well layers of B₀₀₁Ga₀₈₆ln_{0 13}N material together with B₀₀₁Ga₀₉₀ln₀₀₉N. Finally, a ninth embodiment employs B₀₀₁ln₀₀₁AI₀₉₈N material for the cladding layers together with quantum well layers of B₀₀₁ln₀₀₈AI₀₉₁N material together with B₀₀₂ln₀₀₇AI₀₉₁N material. In the seventh and eighth embodiments, it can be seen that the generalized formulation of B₁__x__y__zln_xGa_yAl_zN applies, where z = 0, while for the ninth and tenth embodiments y = 0. It will also be appreciated that pentenary materials systems exist which follow the general formulation of the present invention and for which x, y and z are each non-zero but do not sum to one.

Referring first to Figure 2, shown therein in cross-sectional view is a semiconductor structure according to a first embodiment of the invention. For purposes of illustration, the semiconductor structure shown in many of the Figures will be a laser diode, although the present invention has application to a number of device types. With particular reference to Figure 1 , an n-type GaN substrate 100 is provided and an n-type GaN first cladding layer 105 (typically 0.5μm thick) is formed thereon. Thereafter, a second cladding layer 110, typically of an n-type ln₀₀₅Ga₀₇₅AI_{0 2}N material which may be on the order of 1.5 μm thick, is formed thereon, followed by a multiple quantum well active layer 115 which in an exemplary arrangement may comprise three quantum well layers of ln₀₀₁Ga₀₉₆Al₀₀₃N material on the order of 35A thick together with four barrier layers of ln₀₀₂Ga₀₈₅Al_{0 13}N material on the order of 35A thick, arranged as three pairs. Next, a third cladding layer 120 of a p-type ln₀₀₅Ga₀₇₅AI₀₂N( typically on the order of 1.5 mm thick) is formed, followed by a p-type GaN fifth cladding layer 125 (on the order of 0.5μm thick). A SiO₂ layer 130 having one stripe like window region 135 (3.0μm width) is formed on the p-type GaN fourth cladding layer 125. A first electrode 140 is formed on the n-type GaN substrate 100, while a second electrode 145 is formed on the SiO₂ layer 130 and the window region 135.

In order to emit ultra violet light with a wavelength range of 350 nm from the active layer 115, the InN mole fraction, the GaN mole fraction, and the AIN mole 5 fraction of the well layer are set to be 0.01, 0.96, and 0.03, respectively. To avoid defects due to phase separation, the lattice constants of the various constituent layers are matched to each other by setting the GaN mole fraction, x, and the AIN, y, in each of the layers to meet the condition x + 1.2y nearly equals a constant value. In an exemplary embodiment, the constant value is set to nearly one, for example

10 1 + 0.1 , although most embodiments will be in the range 1 + 0.05.

By proper selection of materials, the band gap energy of the n-type second cladding layer 110 and the p-type third cladding layer 120 are larger than that of the three pairs of multiple quantum well active layers 115. This confines the injected carriers from the n-type second cladding layer 110 and p-type third cladding layer

15 120 within the active layer 115, where the carriers recombine to lead to the emission of ultraviolet light. In addition, the refractive index of the n-type second cladding layer 110 and the p-type third cladding layer 120 are smaller than that of the multiple quantum well active layer 115, which confines the optical field in the transverse direction. 0 Because the injected current from the electrode 145 is confined to flow through the window region 135, the region in the active layer 115 under the widow region 135 is activated strongly. This causes the local modal gain in the active layer under the window region 6a to be higher than the local modal gain in the active layer under the SiO₂ layer. Therefore, a gain guided waveguide, leading to a lasing 5 oscillation, is formed in the structure of the first embodiment.

Figure 3 shows a plot of the emitted light versus drive current for a laser diode constructed in accordance with the first embodiment. The laser diode is driven with a pulsed current with a duty cycle of 1 %. The threshold current density is found to be 5.5 kA/cm². 0 Figures 4A-4D show, in sequence, a summary of the fabrication steps necessary to construct an exemplary laser diode according to the first embodiment. Since the structure which results from Figures 4A-4D will resemble that shown in Figure 2, like reference numerals will be used for elements whenever possible. With reference first to Figure 4A, an n-type GaN substrate 100 is provided, on which is 5 grown an n-type GaN first cladding layer 105. The first cladding layer 105 is typically on the order of 0.5μm thick. Thereafter, an n-type ln₀₀₅Ga₀₇₅AI₀₂N second cladding layer 110 is formed, typically on the order of 1.5 μm thick.

Next, a multiple quantum well active layer 115 is formed by creating three quantum wells comprised of three layers of ln₀₀₁Ga₀₉₆Al₀₀₃N material each on the order of 35A thick, together with four barrier layers of ln₀₀₂Ga₀₈₅AI_{0 13}N material on the order of 35A thick. A third cladding layer 120 of p-type ln₀₀₅Ga₀₇₅AI₀₂N material, on the order of 1.5 μm thick, is then formed, after which is formed a fourth cladding 5 layer 125 of a p-type GaN on the order of 0.5μm thick. Each of the layers is typically formed by eitherthe Metal Organic Chemical Vapor Deposition (MOCVD) method or the Molecular Beam Epitaxy (MBE) method.

Then, as shown in Figure 4B, a silicon dioxide (SiO₂) layer 130 is formed on the p-type GaN fourth cladding layer 125, for example by the Chemical Vapor o Deposition (CVD) method. Using photolithography and etching or any other suitable method, a window region 135 is formed as shown in Figure 4C. The window region 135 may be stripe-like in at least some embodiments. Finally, as shown in Figure 4D, a first electrode 140 and a second electrode 145 are formed on the n-type GaN substrate 100 and on the SiO₂ layer 130, respectively, by evaporation or any other suitable process.

Referring next to Figure 5, a second embodiment of a semiconductor structure in accordance with the present invention may be better appreciated. As with the first embodiment, an exemplary application of the second embodiment is the creation of a laser diode. The structure of the second embodiment permits a waveguide mechanism to be built into the structure with a real refractive index guide. This provides a low threshold current laser diode which can operate with a fundamental transverse mode.

Still with reference to Figure 5, like elements with respect to the first embodiment will be indicated with like reference numerals. On an n-type GaN substrate 100, a first cladding layer 105 is formed of an n-type GaN on the order of -

0.5μm thick. Successively, an n-type second cladding layer 110 is formed of

'ⁿo.o₅Ga_0.75Alo.₂N material on the order of 1.5 μm thick. Thereafter, a multiple quantum well active layer 115 is formed comprising three well layers of ln₀₀₁Ga₀₉₆Al₀₀₃N material on the order of 35A thick together with four barrier layers of ln₀₀₂Ga₀₈₅AI_{0 13}N material, also on the order of 35A thick. Next, a third, p-type cladding layer 120 formed of ln₀₀₅Ga₀₇₅Al₀₂N material on the order of 1.5 μm thick is formed. Thereafter, a p-type GaN fourth cladding layer 125 on the order of 0.5μm thick is formed over the ridge structure 500 of the third cladding layer 120. The third and fourth cladding layers are then partially removed to create a ridge structure 500. A silicon dioxide (SiO₂) layer 130 is then formed over over the fourth cladding layer

125 as well as the remaining exposed portion of the third cladding layer 120. A window region 135, which may be stripe-like on the order of 2.0μm width, is formed through the SiO₂ layer above the fourth and third cladding layers 125 and 120, respectively. As with the first embodiment, a first electrode 140 is formed on the n- type GaN substrate 100 and a second electrode 145 is formed on the SiO₂ layer 130 and the window region 135.

As with the first embodiment, in order to emit ultra violet light with a wavelength in the range of 350 nm from the active layer 14, the mole fractions of InN,

GaN, and AIN in the well layer are set to be 0.01 , 0.96, and 0.03, respectively.

Likewise, in order to match the lattice constants of each of the constituent layers to avoid defects due to phase separation, the GaN mole fraction, x, and the AIN, y, of all the layers satisfy the condition of x + 1.2y nearly equals a constant value. As in the first embodiment, x + 1.2y set to be nearly equals 1 so that the equivalent lattice constants of each layers become nearly equal to the lattice constant of GaN.

Likewise, the band gap energy of the cladding layers is maintained larger than the band gap energy for the active layer, allowing the emission of ultraviolet light.

Similarly the refractive index of the materials is as discussed in connection with the first embodiment, permitting the optical field to be confined in the transverse direction.

Similar to the operation of the first embodiment, the region of the active layer

115 under the window region 135 is activated strongly because of the constraints on the injected current by the SiO2 layer. The result, again, is that the local modal gain in the active layer under the window region 135 is higher than the local modal gain in the active layer under the SiO₂ layer 130. This, combined with the relatively higher effective refractive index in the transverse direction inside the ridge stripe region compared to that outside the ridge stripe region, provides an effective refractive index step (Δn). This results in a structure which has, built in, a waveguide formed by a real refractive index guide. Therefore, the design of the second embodiment provides a low threshold current laser diode which can operate with a fundamental transverse mode.

Figure 6 shows in graph form the emitted light versus drive current characteristics of a laser diode in accordance with the second embodiment. The laser diode is driven with a cw current. The threshold current is found to be 32.5 mA.

Referring next to Figures 7A-7E, a summary of the key fabrication steps is shown for an exemplary device of a semiconductor laser diode in accordance with the second embodiment.

Referring first to Figure 7A and 7B, the formation of the first and second cladding layers 105 and 110 on an n-type GaN substrate 100, together with the three-pair multiple quantum well active layer 115 are the same as for the first embodiment. Thereafter, the third and fourth cladding layers 120 and 125 are formed and then partially removed - typically by etching - to create a ridge structure 500. As before, in an exemplary embodiment the various layers are formed successively by either the MOCVD or the MBE method.

Then, as shown in Figure 7C-7E, a silicon dioxide layer 130 is formed over the fifth and third cladding layers 125 and 120, respectively, typically by the CVD method, after which a window region 135 is formed as with the first embodiment. Electrodes 140 and 145 are then evaporated or otherwise bonded to the structure. Referring next to Figure 8, a third embodiment of the present invention may be better appreciated. The third embodiment provides slightly different mole fractions to permit the emission of blue light, but is otherwise similar to the first embodiment. Thus, an n-type GaN substrate 100 continues to be used, together with an n-type GaN first cladding layer 105. However, the second cladding layer 810 is typically of n-type ln_{0 15}Ga₀₇₀AI_{0 15}N material on the order of 1.5 μm thick, while the three-pair quantum well active layer 815 typically includes three barrier layers of 'ⁿo.i₅G^ao₈ ^AO.oi^N material together with four barrier layers of ln_{0 16}Ga₀₈₀AI₀₀₄N material. The third cladding layer 820 is typically a p-type ln_{0 15}Ga₀₇₀AI_{0 15}N material, while the fourth cladding layer 125 is, like the first embodiment, a p-type GaN material. The thicknesses of each layer are substantially the same as for the first embodiment. A SiO₂ layer 130, window region 135, and first and second electrodes 140 and 145 complete the structure. In order to emit blue light in a wavelength range of 400 nm from the active layer 24, the mole fractions of InN, GaN, and AIN within the well layer 815 are set to be 0.15, 0.84, and 0.01 , respectively. In order to match the lattice constants of the constituent layers to avoid generation of phase separation-induced defects, the GaN mole fraction, x, and the AIN mole fraction, y, of each of the layers is set to satisfy the condition x + 1.2y nearly equals a constant value on the order of 0.85+0.1 ; as before, most embodiments will be in the range 0.85+0.05.

Although the third embodiment emits blue light whereas the first embodiment emits ultraviolet light, the band gap energies of cladding layers continue to be set higher than the band gap energy of the three pairs of the multiple quantum well active layer 815. As before, this permits carrier confinement and recombination in the active layer 815. Also as with the first embodiment, the refractive index of the second and third cladding layers is, by design, smaller than that of the active layer, causing the optical field to be confined in the transverse direction. Likewise, the strong current injection under the window region 135 yields comparatively higher local modal gain in the active layer relative to the portion of the active layer under the SiO2 layer 130, again resulting in a guided waveguide which leads to a lasing oscillation.

Figure 9 shows a plot of the emitted light versus drive current characteristics of the laser diode in accordance with the third embodiment. The laser diode is driven with a pulsed current with a duty cycle of 1 %. The threshold current density is found to be 5.0 kA/cm².

Figures 10A-10D show a series of the fabrication steps of a semiconductor laser diode in one example of the third embodiment. It will be appreciated that the fabrication steps are the same as those described in connection with Figures 4A-4D, and therefore are not further described.

Referring next to Figure 11 , a fourth embodiment of the present invention may be better appreciated. The fourth embodiment, like the third embodiment, is designed to emit blue light and therefore has the same mole fractions as the third embodiment. However, like the second embodiment, the fourth embodiment is configured to provide a ridge structure to serve as a waveguide. Because the mole fractions are similar to those of Figure 8, similar elements will be described with the same reference numerals used in Figure 8. Continuing to refer to Figure 11 , the structure of the fourth embodiment can be seen to have a GaN substrate 100 on which is a formed a first cladding layer 105 followed by a second cladding layer 810. A three-pair multiple quantum well active layer 815 is formed thereabove, followed by a third cladding layer 820. A fourth cladding layer 125, silicon dioxide layer 130, windows 135 and electrodes 140 and 145 are all formed as before. The materials, including the mole fractions of InN,

GaN, and AIN, remain as shown for Figure 8, or 0.15, 0.84, and 0.01 , respectively.

Likewise the GaN mole fraction, x, and the AIN mole fraction, y, of the layers is set to satisfy the condition x + 1.2y is equal to or nearly equal to a constant value on the order of 0.85+0.1 , as with the prior embodiments. The band gap energy, refractive index and modal gain for current injection are all substantially as discussed in connection with the third embodiment and are not further discussed.

Figure 12 plots drive current versus emitted light of a laser diode constructed in accordance with the fourth embodiment. The laser diode is driven with a cw current. The threshold current is found to be 28.5 mA. Figure 13 shows a summary of the fabrication steps of a semiconductor laser diode in accordance with the fourth embodiment. The steps are essentially identical to those discussed in connection with Figures 7A-7E and are not further discussed.

Referring next to Figure 14, the selection of the GaN mole fraction, x, and the

AIN mole fraction, y, and the relationship therebetween for the constituent InGaAIN layers, may be better understood. In particular, the relative mole fractions are required to satisfy, approximately, the relationship 0 < x + y <1 , 1 <= x/0.80 + y/0.89.

Figure 14 shows the boundary of phase separation region plotted against various growth temperatures. The lines in Figure 14 show the boundary between the compositionally unstable (phase separation) region and stable region with respect to various temperatures. The region surrounded with the InN-AIN line and the boundary line shows the phase separation content region. It has been discovered that the ternary alloys InAIN and InGaN have a large phase separation region due 5 to the large lattice mismatch between InN and AIN, and between InN and GaN. On the other hand, it is found that the ternary alloy GaAIN has no phase separation region for crystal growth at temperatures around 1000 °C, due io e small lattice mismatch between AIN and GaN.

It has therefore been discovered that an InGaAIN material system can be

10 provided in which phase separation of the In content, Ga content, and Al content of InGaAIN does not occur significantly when the crystal growth temperature is in the approximate range of around 500 °C to around 1000°C. The content choice region of Ga content and Al content in InGaAIN to avoid phase separation at a crystal growth temperature below around 1000 °C is found to be the shadow region in Figure

15 15, with the line separating the two regions being approximately defined by the relationship x/0.80 + y/0.89 =1.

Therefore, for each of the four structural embodiments disclosed hereinabove, the phase separation phenomena can be avoided in an InGaAIN material system by operating at a crystal growth temperature between on the order of 500 °C and around

20 1000 °C, when the Ga mole fraction, x, and the AIN mole fraction, y, of the all constituent layers of the laser diodes are made to satisfy approximately the relationship of 0 < x + y <1 , 1<= x/0.80 + y/0.89. The result is the substantially uniform distribution of In atoms, Ga atoms, and Al atoms in each constituent layer according to the atomic mole fraction. 5 Figure 16 shows the content choice line of Ga content, x, and Al content, y, in an InGaAIN system to avoid phase separation phenomenon at growth temperatures below around 1000 °C. The line in Figure 16 shows the exemplary line of x + 1.2y = 1. Therefore, by ensuring that the Ga content and Al content of the constituent InGaAIN layers of a laser diode formed on a GaN substrate have a 0 relationship of x + 1.2y nearly equal to 1 and 0 < x + y <1 , 1<= x/0.80 + y/0.89, a laser diode can be fabricated on a GaN substrate with low defect density and no or very little phase separation.

In addition, other semiconductor structures can be fabricated with the materials system discussed above. Group-Ill nitride materials, especially GaN and 5 AIN, are promising for use in electronic devices which can operate under high-power and high-temperature conditions - for example, microwave power transistors. This results, in part, from their wide band gap (3.5 eV for GaN and 6.2 eV for AIN), high breakdown electronic field, and high saturation velocity. By comparison, the band gaps of AIAs, GaAs, and Si are 2.16 eV, 1.42 eV, and 1.12 eV, respectively. This has led to significant research in the use of AIGaN/GaN materials for such field effect transistors (FETs). However, as noted previously hereinabove, the different lattice constants of AIGaN and GaN cause the generation of significant defects, limiting the mobility of electrons in the resultant structure and the utility of such materials systems for FET use.

The present invention substantially overcomes these limitations, in that the InGaAIN/GaN material of the present invention has a lattice constant equal to GaN. As discussed hereinabove, a quaternary materials system of In^_yGa^l_yN, where the GaN mole fraction (x) and AIN mole fraction (y) satisfy the relationships 0 < x + y < 1 , 1<= x/0.8 + y/0.89 and x + 1.2y = 1+0.1 not only has a band gap greater than 3.1 eV, but also has a lattice constant substantially equal to GaN. This permits fabrication of semiconductor structures such as FETs which have substantially uniform atomic content distribution in the various layers. Therefore, by using an InGaAIN/GaN material system in accordance with the present invention, whose GaN mole fraction, x and AIN mole fraction, y satisfy the above relationships, high-power and high-temperature transistors with low defect density can be realized.

Referring to Figure 17A, there is shown therein an exemplary embodiment of a heterojunction field effect transistor(HFET) using InGaAIN/GaN material in accordance with the present invention. On a GaN substrate 520, a 0.5 μm i-GaN layer 525 is formed, followed by a thin, approximately 10 nm GaN conducting channel layer 530 and a 10 nm InGaAIN layer 535. Source and drain electrodes 540A-B, and gate electrode 545 are formed in a conventional manner. In the structure, the GaN mole fraction, x, and AIN mole fraction, y, of the InGaAIN layer are set to be 0.64 and 0.3, respectively. In this case, the value of x and y satisfy the- relationship^'of 0 < x + y < 1 , 1 <= x/0.8 + y/0.89, and x + 1.2y = 1 +0.1. This results in an InGaAIN layer substantially without phase separation and with a lattice constant equal to GaN, In turn, this permits high electron velocities to be achieved because the two dimensional electron gas formed in the heterointerface of InGaAIN and GaN layer is not scattered by any fluctuation in atomic content of the InGaAIN layer (such as would be caused in the presence of defects). Moreover, the band gap of the InGaAIN is larger than 4 eV so that reliable high-temperature operation can be achieved by using the structure shown in Figure 17A.

Similarly, Figure 17B shows an embodiment of a heterojunction bipolar transistor(HBT) in accordance with the present invention. On the GaN substrate 550, a 400 nm thick n-type InGaAIN collector layer 555 is formed, followed by a 50 nm thick p-type GaN base layer 560, and a 300 nm thick emitter layer 565. Base electrode 570, collector electrode 575 and emitter electrode 580 are formed conventionally. As with Figure 17A, for the exemplary embodiment of Figure 17B the GaN and AIN mole fractions x and y of the InGaAIN layer are set to be 0.64 and 0.3, respectively, and x and y are required to satisfy the same relationships as discussed above. As with Figure 17A, an InGaAIN layer without significant phase separation and with a lattice constant equal to GaN is realized, resulting in a very high quality heterojunction of InGaAIN/GaN. In addition, the band gap of the InGaAIN emitter layer (4.2 eV) is larger than that of GaN base layer (3.5eV) so that holes generated in the p-type base layer are well confined in that base layer. This results because of the largervalence band discontinuity between GaN and InGaAIN than would occur in a GaN homojunction bipolar transistor. This has the benefit of obtaining a large current amplification of collector current relative to base current. Moreover, as mentioned above, the bandgap of the InGaAIN and the GaN layer is large so that the transistor can be used reliably in high-temperature applications.

Referring next to Figure 18, there is shown therein an implementation of the present invention as a phototransistor. In this regard, GaN and AIGaN are attractive materials for photo detectors in ultraviolet(UV) range, since both GaN and AIN have a wide band gap (3.5 eV for GaN which corresponds to the light wavelength of 200 nm, 6.2 eV for AIN which corresponds to the light wavelenght of 350 nm). Due to the direct band gap and the availability of AIGaN in the entire AIN alloy composition range, AIGaN/GaN based UV photo detectors have the advantage of high quantum efficiency, as well as tunability of high cut-off wavelength. However, the lattice constant of AIGaN is sufficiently different from GaN that defects tend to be formed, which leads increased leakage current.

An In^_yGa_xAl_yN quaternary material whose GaN mole fraction, x and AIN mole fraction, y satisfy the relationship of0 < x + y < 1 , 1<= x/0.8 + y/0.89, offers not only a band gap larger than 3.1 eV, but also can be fabricated in layers with equal atomic content distribution, so that InGaAIN material also can be used for UV photo detector applications. Moreover, the In^_yGa^l_yN quaternary material whose GaN mole fraction, x and AIN mole fraction, y satisfy the relationship of x + 1.2y = 1 has a lattice constant equal to GaN. Therefore, by using an InGaAIN/GaN material whose GaN mole fraction, x and AIN mole fraction, y satisfy the above relationship, UV photo detectors with low defect density can be realized. In the event that detection of other frequencies is desired, for example blue light, only slight modification is required as will be understood by those skilled in the art. As shown in Figure 18, the semiconductor device of the present invention can be implemented as a heterojunction phototransistor(HPT) using an InGaAIN/GaN material. On the GaN substrate 700, an InGaAIN collector layer 705 is formed on the order of 500 nm thick n-type, followed by the formation of a 200 nm thick p-type GaN base layer 710. Thereafter, an emitter layer 715 on the order of 500 nm thick is formed. On the emitter layer, a ring shaped electrode 720 is formed to permit light to impinge on the base layer.

In an exemplary structure, the GaN mole fraction, x and AIN mole fraction, y of the InGaAIN layer are set to be 0.64 and 0.3, respectively. In this case, the value of x and y satisfy the relationship of 0 < x + y < 1 , 1 <= x/0.8 + y/0.89, and x + 1.2y =

1 , so that an InGaAIN layer can be formed with substantially avoids phase separation while having a lattice constant equal to GaN, thus permitting the formation of a high quality heterojunction of InGaAIN/GaN. The band gap of the InGaAIN emitter layer (4.2 eV which corresponds to the light wavelength of 290 nm) is larger than that of

GaN base layer (3.5eV which corresponds to the light wavelength of 350 nm). The light impinges on the emitter side. For the embodiment shown, impinging light in the wavelength range between 290 nm and 350 nm is transparent to the emitter layer, so that the light in that range is absorbed in the GaN base layer and generates electron and hole pairs. The holes generated by the optical absorption in the p-type base layer are well confined in the base layer because the valence band discontinuity between GaN and InGaAIN is larger than that for a conventional GaN homojunction photo transistor. This leads to the induction of a larger emitter current, which offers better electronic neutralization in the base region than in the case of the homojunction photo transistor. Therefore, UV photo detectors with high quantum efficiency and high sensitivity, and the resultant high conversion efficiency from input light to collector current, are obtained. In the event that other frequencies are to be detected, the GaN base layer may be replaced with, for example for blue light,

InGaN. In addition to the phototransistor of Figure 18, it is also possible to implement a photodiode in accordance with the present invention. Referring to Figure 19, an n- type GaN substrate 900 is provided, on which is formed an n-type layer 910 of In^. _yGa_χAl_yN q u ate rn a ry material or equivalent, which conforms to the relationships discussed above in connection with Figure 18. An active layer 915 is thereafter formed, and above that is formed a layer 920 of p-type In^Ga_xAl_yN quaternary material. Then, a p-type second cladding layer 925 is formed above the layer 920, and a window 930 is formed therein to expose a portion of the layer 920.The window

930 provides a port by which light can impinge on the layer 920, causing the creation of holes. A pair of electrodes 935 and 940 may be fabricated in a conventional manner, with the electrode 935 typically being a ring electrode around the window

930. It will be appreciated that the band gap of the second cladding layer 925 is preferably larger than the band gap of the layer 920, which is in turn preferably larger than the band gap of the active layer 915; such an approach provides sensitivity to the widest range of wavelength of light. If the event a narrower range is desired, a material with a lower band gap than the layer 920 may be used for the layer 925. In addition, it is also not necessary to include the layer 925 in all embodiments, as the layers 910, 915 and 920 provide, in at least some instances, an adequate photosensitive pn-junction.

Referring next to Figure 20, a fifth embodiment of the present invention may be better appreciated. The fifth embodiment uses BAIGaN quaternary material system to provide an UV light emitting devices. Referring to Figure 20, shown therein in cross-sectional view is a semiconductor structure according to a fifth embodiment of the invention. A diode of the fifth embodiment with particular reference to Figure

20, an n-type AIN substrate 200 is provided and an n-type AIN first cladding layer

205 (typically 0.5μm thick) is formed thereon. Thereafter, a second cladding layer

210, typically of an n-type B₀₀₁AI₀₉₅Ga₀₀₄N material which may be on the order of 1.5 μm thick, is formed thereon, followed by a multiple quantum well active layer 215 which in an exemplary arrangement may comprise three quantum well layers of

B₀₀₄AI₀₆₃Ga₀₃₃N material on the order of 35A thick together with four barrier layers of B₀₀₃AI₀₇₀Ga₀₂₇N material on the order of 35A thick, arranged as three pairs. Next, a third cladding layer 220 of a p-type B₀₀₁AI₀₉₅Ga₀₀₄N ( typically on the order of 1.5 μm thick) is formed, followed by a p-type AIN fifth cladding layer 225 (on the order of 0.5μm thick). A SiO₂ layer 230 having one stripe like window region 235 (3.0μm width) is formed on the p-type AIN fourth cladding layer 225. A first electrode 240 is formed on the n-type AIN substrate 200, while a second electrode 245 is formed on the SiO₂ layer 230 and the window region 235.

In order to emit ultra violet light with a wavelength range of 230 nm from the active layer 215, the BN mole fraction, the GaN mole fraction, and the AIN mole fraction of the well layer are set to be 0.04, 0.63, and 0.33, respectively. To avoid defects due to lattice mismatch, the lattice constants of the various constituent layers are matched to each other by setting the AIN mole fraction, x, and the GaN, y, in each of the layers to meet the condition x + 1.12y nearly equals a constant value. In an exemplary embodiment, the constant value is set to nearly one, for example 1±0.1 , although most embodiments will be in the range 1±0.05.

By proper selection of materials, the band gap energy of the n-type second cladding layer 210 and the p-type third cladding layer 220 are larger than that of the 3 pairs of multiple quantum well active layers 215. This confines the injected carriers from the n-type second cladding layer 210 and p-type third cladding layer 220 within the active layer 215, where the carriers recombine to lead to the emission of ultraviolet light. In addition, the refractive index of the n-type second cladding layer 210 and the p-type third cladding layer 220 are smaller than that of the multiple quantum well active layer 215, which confines the optical field in the transverse direction.

Because the injected current from the electrode 245 is confined to flow through the window region 235, the region in the active layer 215 under the widow 5 region 235 is activated strongly. This causes the local modal gain in the active layer under the window region to be higher than the local modal gain in the active layer under the SiO₂ layer. Therefore, a gain guided waveguide, leading to a lasing oscillation, is able to be formed in the structure of the fifth embodiment.

Figures 21A-21 D show, in sequence, a summary of the fabrication steps 10 necessary to construct an exemplary laser diode according to the fifth embodiment. Since the structure which results from Figures 21 A-21 D will resemble that shown in Figure 20, like reference numerals will be used for elements whenever possible. With reference first to Figure 21 A, an n-type AIN substrate 200 is provided, on which is grown an n-type AIN first cladding layer 205. The first cladding layer 205 is 15 typically on the order of 0.5μm thick. Thereafter, an n-type B₀₀₁AI₀₉₅Ga₀₀₄N second cladding layer 210 is formed, typically on the order of 1.5 μm thick.

Next, a multiple quantum well active layer 215 is formed by creating three quantum wells comprised of three layers of of B₀₀₄AI₀₆₃Ga₀₃₃N material each on the order of 35A thick, together with four barrier layers of B₀₀₃AI₀₇₀Ga₀₂₇N material on the 20 order of 35A thick. A third cladding layer 220 of p-type B₀₀₁ Al₀₉₅Ga₀ ^N material, on the order of 1.5 μm thick, is then formed, after which is formed a fourth cladding layer 225 of a p-type AIN on the order of 0.5μm thick. Each of the layers is typically formed by either the Metal Organic Chemical Vapor Deposition (MOCVD) method or the Molecular Beam Epitaxy (MBE) method. 25 Then, as shown in Figure 21 B, a silicon dioxide (SiO₂) layer 230 is formed on the p-type AIN fourth cladding layer 225, for example by the Chemical Vapor Deposition (CVD) method. Using photolithography and etching or any other suitable method, a window region 235 is formed as shown in Figure 21 C. The window region 235 may be stripe-like in at least some embodiments. Finally, as shown in Figure 30 21 D, a first electrode 240 and a second electrode 245 are formed on the n-type AIN substrate 200 and on the SiO₂ layer 230, respectively, by evaporation or any other suitable process.

Referring next to Figure 22, a sixth embodiment of a semiconductor structure in accordance with the present invention may be better appreciated. As with the fifth 5 embodiment, an exemplary application of the sixth embodiment is the creation of a laser diode. The structure of the sixth embodiment permits a waveguide with a real refractive index guide to be built into the structure. This provides a low threshold current laser diode which can operate with a fundamental transverse mode. Continuing with reference to Figure 22, for ease of reference, like elements will be indicated with like reference numerals. On an n-type AIN substrate 200, a first cladding layer 205 is formed of an n-type AIN on the order of 0.5μm thick.

Successively, an n-type second cladding layer 210 is formed of B₀₀₁AI₀₉₅Ga₀₀₄N material on the order of 1.5 μm thick. Thereafter, a multiple quantum well active layer 215 is formed comprising three well layers of B₀₀₄AI₀₆₃Ga₀₃₃N material on the order of 35A thick together with four barrier layers of B₀₀₃AI₀₇₀Ga₀₂₇N material, also on the order of 35A thick. Next, a third, p-type cladding layer 220 formed of

B₀₀₁AI₀₉₅Ga₀₀₄N material on the order of 1.5 μm thick is formed. Thereafter, a p-type AIN fourth cladding layer 225 on the order of 0.5μm thick is formed over the ridge structure 1500 of the third cladding layer 220. The third and fourth cladding layers are then partially removed to create a ridge structure 1500. A silicon dioxide (SiO₂) layer 230 is then formed over the fourth cladding layer 225 as well as the remaining exposed portion of the third cladding layer 220. A window region 235, which may be stripe-like on the order of 2.0μm width, is formed through the SiO₂ layer above the fourth and third cladding layers 225 and 220, respectively. As with the fifth embodiment, a first electrode 240 is formed on the n-type AIN substrate 200 and a second electrode 245 is formed on the SiO₂ layer 230 and the window region 235.

As with the fifth embodiment, in order to emit ultra violet light with a wavelength in the range of 230 nm from the active layer 215, the mole fractions of

BN, GaN, and AIN in the well layer are set to be 0.04, 0.33, and 0.63, respectively.

Likewise, in order to match the lattice constants of each of the constituent layers to avoid defects due to lattice mismatch, the AIN mole fraction, x, and the GaN, y, of all the layers satisfy the condition of x + 1.12y nearly equals a constant value. As in the fifth embodiment, x + 1.12y set to be nearly equals 1 so that the equivalent lattice constants of each layers become nearly equal to the lattice constant of AIN.

Similar to the operation of the fifth embodiment, the region of the active layer 215 under the window region 235 is activated strongly because of the constraints on the injected current by the SiO₂ layer. The result, again, is that the local modal gain in the active layer under the window region 235 is higher than the local modal gain in the active layer under the SiO₂ layer 230. This, combined with the relatively higher effective refractive index in the transverse direction inside the ridge stripe region compared to that outside the ridge stripe region, provides an effective refractive index step (Δn). This results in a structure which has, built in, a waveguide formed by a real refractive index guide. Therefore, the design of the sixth embodiment provides a low threshold current laser diode which can operate with a fundamental transverse mode. Referring next to Figures 23A-23E, a summary of the key fabrication steps is shown for an exemplary device of a semiconductor laser diode in accordance with the fifth embodiment.

Referring first to Figure 23A and 23B, the formation of the first and second cladding layers 205 and 210 on an n-type AIN substrate 200, together with the three- pair multiple quantum well active layer 215 are the same as forthe fifth embodiment.

Thereafter, the third and fourth cladding layers 220 and 225 are formed and then partially removed - typically by etching - to create a ridge structure 1500. As before, in an exemplary embodiment the various layers are formed successively by either the

MOCVD or the MBE method. Then, as shown in Figure23C-23E, a silicon dioxide layer 230 is formed over the fifth and third cladding layers 225 and 220, respectively, typically by the CVD method, after which a window region 235 is formed as with the fifth embodiment.

Electrodes 240 and 245 are then evaporated or otherwise bonded to the structure_..

Referring next to Figure 24, the selection of the AIN mole fraction, x, and the GaN mole fraction, y, and the relationship therebetween for the constituent BAIGaN layers, may be better understood. In particular, the relative mole fractions are required to satisfy, approximately, the relationship 0 < x + y <1 , 1 <= 1.04x + 1.03y.

Figure 24 shows the boundary of phase separation region plotted against various growth temperatures. The lines in Figure 24 show the boundary between the compositionally unstable (phase separation) region and stable region with respect to various temperatures. The region surrounded with the two boundary lines forthe same temperature shows the phase separation content region for each temperature.

It has been discovered that the ternary alloys BAIN and BGaN have a large phase separation region due to the large lattice mismatch between BN and AIN, and between BN and GaN. On the other hand, it is found that the ternary alloy GaAIN has no phase separation region for crystal growth at temperatures around 1000 °C, due to the small lattice mismatch between AIN and GaN.

It has therefore been discovered that an BGaAIN material system can be provided in which the usual crystal growth temperature is in the approximate range of around 500 °C to around 1000 °C like in the case of InGaAIN. Likewise, it has been discovered that phase separation of the B content, Ga content, and Al content of BGaAIN does not occur significantly at processing temperatures between on the order of 500 °C and on the order of 1000 °C. Finally, by combining the two, the content choice region of Ga content and Al content in BGaAIN to avoid phase separation at a crystal growth temperature below around 1000 °C is found to be the shadow region in Figure 25, with the line separating the two regions being approximately defined by the relationship 1.04x + 1.03y =1. Therefore, for each of the two structural embodiments using BAIGaN disclosed hereinabove, the phase separation phenomena can be avoided in an BGaAIN material system by operating at a crystal growth temperature between on the order of 500 °C and around 1000 °C, when the Al mole fraction, x, and the GaN mole fraction, y, of the all constituent layers of the laser diodes are made to satisfy approximately the relationship of 0 < x + y <1 , 1<= 1.04x + 1.03y. The result is the substantially uniform distribution of B atoms, Ga atoms, and Al atoms in each constituent layer according to the atomic mole fraction.

Figure 26 shows the content choice line of Al content, x, and Ga content, y, in an BGaAIN system to avoid phase separation phenomenon at growth temperatures below around 1000 °C. The line in Figure 26 shows the exemplary line of x + 1.12y = 1. Therefore, by ensuring that the Ga content and Al content of the constituent BGaAIN layers of a laser diode formed on a AIN substrate have a relationship of x + 1.12y nearly equal to 1 and 0 < x + y <1, 1<= 1.04x + 1.03y, a laser diode on a AIN substrate with low defect density and no or very little phase separation can be obtained.

In addition, other semiconductor structures can be fabricated with BAIGaN materials system. As discussed above, Group-Ill nitride materials, especially GaN and AIN, are promising for use in electronic devices which can operate under high- power and high-temperature conditions - for example, microwave power FETs by using AIGaN/GaN heterostructures. However, as noted previously hereinabove, the different lattice constants of AIGaN and GaN cause the generation of significant defects, limiting the mobility of electrons in the resultant structure and the utility of such materials systems for FET use.

The present invention also substantially overcomes these limitations, in that the BGaAIN/AIN material of the present invention has a lattice constant equal to AIN. As discussed hereinabove, a quaternary materials system of B^._yA Ga_yN, where the AIN mole fraction (x) and GaN mole fraction (y) satisfy the relationships 0 < x + y < 1 , 1 <= 1.04x + 1.03y and x + 1.12y = 1 ±0.1 not only has a band gap greater than 5 eV, but also has a lattice constant substantially equal to AIN. This permits fabrication of semiconductor structures such as FETs which have substantially uniform atomic content distribution in the various layers. Therefore, by using an BGaAIN/AIN material system in accordance with the present invention, whose AIN mole fraction, x and GaN mole fraction, y satisfy the above relationships, high-power and high- temperature transistors with low defect density can be realized.

Referring to Figure 27A, there is shown therein an exemplary embodiment of a heterojunction field effect transistor(HFET) using BGaAIN/AIN material in accordance with the present invention. On a AIN substrate 1520, a 0.5 μm i- 5 B₀₀₄Al₀₆₃Ga₀₃₃N layer 1525 is formed, followed by a thin, approximately 10 nm B₀₀₄AI₀₆₃Ga₀₃₃N conducting channel layer 1530 and a 10 nm AIN layer 1535. Source and drain electrodes 1540A-B, and gate electrode 1545 are formed in a conventional manner. In the structure, the AIN mole fraction, x, and GaN mole fraction, y, of the BGaAIN layer are set to be 0.63 and 033, respectively. In this case, the value of x 10 and y satisfy the relationship of 0 < x + y < 1 , 1<= 1.04x + 1.03y, and x + 1.12y = 1±0.1. This results in an BGaAIN layer substantially without phase separation and with a lattice constant equal to AIN, In turn, this permits high electron velocities to be achieved because the two dimensional electron gas formed in the heterointerface of BGaAIN and AIN layer is not scattered by any fluctuation in atomic content of the 15 BGaAIN layer (such as would be caused in the presence of defects). Moreover, the band gap of the BGaAIN is larger than 5 eV so that reliable high-temperature operation can be achieved by using the structure shown in Figure 27A.

Similarly, Figure 27B shows an embodiment of a heterojunction bipolar transistor(HBT) in accordance with the present invention. On the AIN substrate

20 1550, a 400 nm thick n-type AIN collector layer 1555 is formed, followed by a 50 nm thick p-type BAIGaN base layer 1560, and a 300 nm thick AIN emitter layer 1565.

Base electrode 1570, collector electrode 1575 and emitter electrode 1580 are formed conventionally. As with Figure 27A, forthe exemplary embodiment of Figure 26B the

AIN and GaN mole fractions x and y of the BGaAIN layer are set to be 0.63 and 0.33,

25 respectively, and x and y are required to satisfy the same relationships as discussed above. As with Figure 27A, an BGaAIN layer without significant phase separation and with a lattice constant equal to AIN is realized, resulting in a very high quality heterojunction of BGaAIN/GaN. In addition, the band gap of the AIN emitter layer

(6.2 eV) is larger than that of BGaAIN base layer (5.3 eV) so that holes generated in 0 the p-type base layer are well confined in that base layer. This results because of the larger valence band discontinuity between AIN and BGaAIN than would occur in a AIN homojunction bipolar transistor. This has the benefit of obtaining a large current amplification of collector current relative to base current. Moreover, as mentioned above, the bandgap of the BGaAIN and the AIN layer is large so that the 5 transistor can be used reliably in high-temperature applications.

Referring next to Figure 28, there is shown therein an implementation of the present invention as a phototransistor.

B^._yA Ga_yN quaternary material whose AIN mole fraction, x and GaN mole fraction, y satisfy the relationship of 0 < x + y < 1 , 1<= 1.04x + 1.03y, offers not only a band gap larger than 3.5 eV, but also can be fabricated in layers with equal atomic content distribution, so that BGaAIN material also can be used for UV photo detector applications. Moreover, the B^_yA Ga_yN quaternary material whose AIN mole fraction, x and GaN mole fraction, y satisfy the relationship of x + 1.12y = 1 has a lattice constant equal to AIN. Therefore, by using BGaAIN/AIN material whose AIN mole fraction, x and GaN mole fraction, y satisfy the above relationship, UV photo detectors with low defect density can be realized. In the event that detection of other frequencies is desired, for example blue light, only slight modification is required. As shown in Figure 28, the semiconductor device of the present invention can be implemented as a heterojunction phototransistor(HPT) using BGaAIN/AIN material. On the AIN substrate 1700, an AIN collector layer 1705 is formed on the order of 500 nm thick n-type, followed by the formation of a 200 nm thick p-type BAIGaN base layer 1710. Thereafter, an emitter layer 1715 on the order of 500 nm thick is formed. On the emitter layer, a ring shaped electrode 1720 is formed to permit light to impinge on the base layer.

In an exemplary structure, the AIN mole fraction, x and GaN mole fraction, y of the BAIGaN layer are set to be 0.63 and 0.33, respectively. In this case, the value of x and y satisfy the relationship of 0 < x + y < 1 , 1<= 1.04x + 1.03y, and x + 1.12y = 1 , so that a BGaAIN layer can be formed with substantially avoids phase separation while having a lattice constant equal to AIN, thus permitting the formation of a high quality heterojunction of BGaAIN/AIN. The band gap of the AIN emitter layer

(6.2 eV which corresponds to the light wavelength of 200 nm) is larger than that of

BAIGaN base layer (5.3eV which corresponds to the light wavelength of 230 nm). The light impinges on the emitter side. For the embodiment shown, impinging light in the wavelength range between 200 nm and 230 nm is transparent to the emitter layer, so that the light in that range is absorbed in the BAIGaN base layer and generates electron and hole pairs. The holes generated by the optical absorption in the p-type base layer are well confined in the base layer because the valence band discontinuity between AIN and BAIGaN is larger than that for a conventional AIN homojunction photo transistor. This leads to the induction of a larger emitter current, which offers better electronic neutralization in the base region than in the case of the homojunction photo transistor. Therefore, UV photo detectors with high quantum efficiency and high sensitivity, and the resultant high conversion efficiency from input light to collector current, are obtained. In the event that other frequencies are to be detected, the BAIGaN base layer may be replaced with, for example for blue light,

InGaN.

In addition to the phototransistor of Figure 28, it is also possible to implement a photodiode in accordance with the present invention. Referring to Figure 29, an n- type AIN substrate 1900 is provided, on which is formed an n-type layer 910 of B,^. _yAl_xGa_yN quaternary material or equivalent, which conforms to the relationships discussed above in connection with Figure 28. An active layer 1915 is thereafter

5 formed, and above that is formed a layer 1920 of p-type B^_yA Ga_yN quaternary material. Then, a p-type second cladding layer 1925 is formed above the layer 1920, and a window 1930 is formed therein to expose a portion of the layer 1920.The window 1930 provides a port by which light can impinge on the layer 1920, causing the creation of holes. A pair of electrodes 1935 and 1940 may be fabricated in a o conventional manner, with the electrode 1935 typically being a ring electrode around the window 1930. It will be appreciated that the band gap of the second cladding layer 1925 is preferably larger than the band gap of the layer 1920, which is in turn preferably larger than the band gap of the active layer 1915; such an approach provides sensitivity to the widest range of wavelength of light. If the event a narrower range is desired, a material with a lower band gap than the layer 1920 may be used for the layer 1925. In addition, it is also not necessary to include the layer 1925 in all embodiments, as the layers 1910, 1915 and 1920 provide, in at least some instances, an adequate photosensitive pn-junction.

Referring next to Figure 30, a seventh embodiment of the present invention may be better appreciated. The seventh embodiment uses BGalnN quaternary material system to provide blue light emitting devices. Referring to Figure 28, shown therein in cross-sectional view is a semiconductor structure according to a seventh embodiment of the invention. A diode of the seventh embodiment with particular reference to Figure 30, an n-type GaN substrate 300 is provided and an n-type GaN first cladding layer 305 (typically 0.5μm thick) is formed thereon. Thereafter,- a second cladding layer 310, typically of an n-type B₀₀₃Ga₀₉₆ln₀₀₁N material which may be on the order of 1.5 μm thick, is formed thereon, followed by a multiple quantum well active layer 315 which in an exemplary arrangement may comprise three quantum well layers of B₀₀₁Ga₀₈₆ln_{0 13}N material on the order of 35A thick together with four barrier layers of B₀₀₁Ga₀₉₀ln₀₀₉N material on the order of 35A thick, arranged as three pairs. Next, a third cladding layer 320 of a p-type B₀₀₃Ga₀₉₆ln₀₀₁N

( typically on the order of 1.5 μm thick) is formed, followed by a p-type GaN fifth cladding layer 325 (on the order of 0.5μm thick). A SiO₂ layer 330 having one stripe like window region 335 (3.0μm width) is formed on the p-type GaN fourth cladding layer 325. A first electrode 340 is formed on the n-type GaN substrate 300, while a second electrode 345 is formed on the SiO₂ layer 330 and the window region 335.

In order to emit blue light with a wavelength range of 400 nm from the active layer 315, the BN mole fraction, the GaN mole fraction, and the InN mole fraction of the well layer are set to be 0.01 , 0.86, and 0.13, respectively. To avoid defects due to lattice mismatch, the lattice constants of the various constituent layers are matched to each other by setting the GaN mole fraction, x, and the InN, y, in each of the layers to meet the condition x + 1.56y nearly equals a constant value. In an 5 exemplary embodiment, the constant value is set to nearly 1.01 , for example 1.01 ±0.1 , although most embodiments will be in the range 1.01 ±0.05.

By proper selection of materials, the band gap energy of the n-type second cladding layer 310 and the p-type third cladding layer 320 are larger than that of the

3 pairs of multiple quantum well active layers 315. This confines the injected carriers

10 from the n-type second cladding layer 310 and p-type third cladding layer 320 within the active layer 315, where the carriers recombine to lead to the emission of blue light. In addition, the refractive index of the n-type second cladding layer 310 and the p-type third cladding layer 320 are smaller than that of the multiple quantum well active layer 315, which confines the optical field in the transverse direction.

15 Because the injected current from the electrode 345 is confined to flow through the window region 335, the region in the active layer 315 under the widow region 335 is activated strongly. This causes the local modal gain in the active layer under the window region to be higher than the local modal gain in the active layer under the SiO₂ layer. Therefore, a gain guided waveguide is formed, leading to lasing

20 oscillation in the structure of the seventh embodiment.

Figures 31A-31 D show, in sequence, a summary of the fabrication steps necessary to construct an exemplary laser diode according to the seventh embodiment. Since the structure which results from Figures 31 A-31 D will resemble that shown in Figure 30, like reference numerals will be used for elements whenever

25 possible. With reference first to Figure 31A, an n-type GaN substrate 300 is provided, on which is grown an n-type GaN first cladding layer 305. The first cladding layer 305 is typically on the order of 0.5μm thick. Thereafter, an n-type

Bo.o₃Ga₀.₉₆Ga₀₀₁N second cladding layer 310 is formed, typically on the order of 1.5 μm thick.

30 Next, a multiple quantum well active layer 315 is formed by creating three quantum wells comprised of three layers of of B₀₀₁Ga₀₈₆ln_{0 13}N material each on the order of 35A thick, together with four barrier layers of B₀₀₁Ga₀₉₀ln₀₀₉N material on the order of 35A thick. A third cladding layer 320 of p-type B₀₀₁Ga₀₉₆ln₀₀₁N material, on the order of 1.5 μm thick, is then formed, after which is formed a fourth cladding layer

35 325 of a p-type GaN on the order of 0.5μm thick. Each of the layers is typically formed by either the Metal Organic Chemical Vapor Deposition (MOCVD) method or the Molecular Beam Epitaxy (MBE) method.

Then, as shown in Figure 31 B, a silicon dioxide (SiO₂) layer 330 is formed on the p-type GaN fourth cladding layer 325, for example by the Chemical Vapor Deposition (CVD) method. Using photolithography and etching or any other suitable method, a window region 335 is formed as shown in Figure 31 C. The window region 335 may be stripe-like in at least some embodiments. Finally, as shown in Figure 31 D, a first electrode 340 and a second electrode 345 are formed on the n-type GaN substrate 300 and on the SiO₂ layer 330, respectively, by evaporation or any other suitable process.

Referring next to Figure 32, an eighth embodiment of a semiconductor structure in accordance with the present invention may be better appreciated. As with the seventh embodiment, an exemplary application of the eighth embodiment is the creation of a laser diode. The structure of the eighth embodiment permits a waveguide with a real refractive index guide to be built into the structure. This provides a low threshold current laser diode which can operate with a fundamental transverse mode. Continuing with reference to Figure 32, for ease of reference, like elements will be indicated with like reference numerals. On an n-type GaN substrate 300, a first cladding layer 305 is formed of an n-type GaN on the order of 0.5μm thick. Successively, an n-type second cladding layer 310 is formed of B₀₀₃Ga₀₉₆ln₀₀₁N material on the order of 1.5 μm thick. Thereafter, a multiple quantum well active layer 315 is formed comprising three well layers of B₀₀₁Ga₀₈₆ln_{0 13}N material on the order of 35A thick together with four barrier layers of B₀₀₁Ga₀₉₀ln₀₀₉N material, also on the order of 35A thick. Next, a third, p-type cladding layer 320 formed of Bo_.o₃G^ao_.96'ⁿo.oιN material on the order of 1.5 μm thick is formed. Thereafter, a p-type GaN fourth cladding layer 325 on the order of 0.5μm thick is formed over the ridge structure 2500 of the third cladding layer 320. The third and fourth cladding layers are then partially removed to create a ridge structure 2500. A silicon dioxide (SiO₂) layer 330 is then formed over the fourth cladding layer 325 as well as the remaining exposed portion of the third cladding layer 320. A window region 335, which may be stripe-like on the order of 2.0μm width, is formed through the SiO₂ layer above the fourth and third cladding layers 325 and 320, respectively. As with the seventh embodiment, a first electrode 340 is formed on the n-type GaN substrate 300 and a second electrode 345 is formed on the SiO₂ layer 330 and the window region 335.

As with the seventh embodiment, in order to emit blue light with a wavelength in the range of 400 nm from the active layer 315, the mole fractions of BN, GaN, and AIN in the well layer are set to be 0.01, 0.86, and 0.13, respectively. Likewise, in order to match the lattice constants of each of the constituent layers to avoid defects due to lattice mismatch, the GaN mole fraction, x, and the AIN, y, of all the layers satisfy the condition of x + 1.56y nearly equals a constant value. As in the seventh embodiment, x + 1.56y set to be nearly equals 1.01 so that the equivalent lattice constants of each layers become nearly equal to the lattice constant of GaN. Likewise, the band gap energy of the cladding layers is maintained larger than the band gap energy for the active layer, allowing the emission of ultraviolet light. Similarly the refractive index of the materials is as discussed in connection with the first embodiment, permitting the optical field to be confined in the transverse direction.

Similar to the operation of the fifth embodiment, the region of the active layer 315 under the window region 335 is activated strongly because of the constraints on the injected current by the SiO₂ layer. The result, again, is that the local modal gain in the active layer under the window region 335 is higher than the local modal gain in the active layer underthe SiO₂ layer 330. This, combined with the relatively higher effective refractive index in the transverse direction inside the ridge stripe region compared to that outside the ridge stripe region, provides an effective refractive index step (Δn). This results in a structure which has, built in, a waveguide with a real refractive index guide. Therefore, the design of the sixth embodiment provides a low threshold current laser diode which can operate with a fundamental transverse mode.

Referring next to Figures 33A-33E, a summary of the key fabrication steps is shown for an exemplary device of a semiconductor laser diode in accordance with the seventh embodiment.

Referring first to Figure 33A and 33B, the formation of the first and second cladding layers 305 and 310 on an n-type GaN substrate 300, together with the three-pair multiple quantum well active layer 315 are the same as for the seventh embodiment. Thereafter, the third and fourth cladding layers 320 and 325 are formed and then partially removed - typically by etching - to create a ridge structure 2500. As before, in an exemplary embodiment the various layers are formed successively by either the MOCVD or the MBE method.

Then, as shown in Figure33C-33E, a silicon dioxide layer 330 is formed over the fifth and third cladding layers 325 and 320, respectively, typically by the CVD method, after which a window region 335 is formed as with the fifth embodiment.

Electrodes 340 and 345 are then evaporated or otherwise bonded to the structure.

Referring next to Figure 34, the selection of the GaN mole fraction, x, and the

AIN mole fraction, y, and the relationship therebetween forthe constituent BGalnN layers, may be better understood. In particular, the relative mole fractions are required to satisfy, approximately, the relationship 0 <= x + y <=1 and 1<= 1.03x +

0.88y, or 0 <= x + y <1 and 1<= 0.95x + 1.01y

Figure 34 shows the boundary of phase separation region plotted against various growth temperatures. The lines in Figure 34 show the boundary between the compositionally unstable (phase separation) region and stable region with respect to various temperatures. The region surrounded with the two boundary lines for the same temperature shows the phase separation content region for each temperature. It has been discovered that the ternary alloys BGaN, BlnN, and InGaN have a large phase separation region due to the large lattice mismatch between BN and GaN, between BN and InN, and between InN and GaN. Therefore, the quaternary alloy

BGalnN has a wide phase separation region, and also each atomic content of B, Ga, and In should be chosen carefully for the application of the devices. It has been discovered that an BGalnN material system can be provided in which the usual crystal growth temperature is in the approximate range of around

500 °C to around 1000 °C like in the case of InGaAIN. Likewise, it has been discovered that phase separation of the B content, Ga content, and In content of

BGalnN does not occur significantly at processing temperatures between on the order of 500 °C and on the order of 1000 °C. Finally, by combining the two, the content choice region of Ga content and In content in BGalnN to avoid phase separation at a crystal growth temperature below around 1000 °C is found to be the shadow region in Figure 35, with the line separating the two regions being approximately defined by the relationship 1.03x + 0.88y =1 and 0.95x + 1.01y=1. Therefore, for each of the two structural embodiments using BGalnN disclosed hereinabove, the phase separation phenomena can be avoided in an BGalnN material system by operating at a crystal growth temperature between on the order of 500 °C and around 1000 °C, when the Ga mole fraction, x, and the InN mole fraction, y, of the all constituent layers of the laser diodes are made to satisfy approximately the relationship of 0 <= x + y <=1 and 1<= 1.03x + 0.88y, or 0 <= x + y <=1 and 1<= 0.95x + 1.01 y. The result is the substantially uniform distribution of

B atoms, Ga atoms, and In atoms in each constituent layer according to the atomic mole fraction.

Figure 36 shows the content choice line of Ga content, x, and Al content, y, in an BGalnN system to avoid phase separation phenomenon at growth temperatures below around 1000 °C. The line in Figure 36 shows the exemplary line ofx + 1.56y = 1.08. Therefore, by ensuring that the Ga content and In content of the constituent BGaAIN layers of a laser diode formed on a GaN substrate have a relationship of x + 1.56y nearly equal to 1.01 , 0 <= x + y <=1 , and 1 <= 1.03x + 0.88y, a laser diode on a GaN substrate with low defect density and no or very little phase separation can be obtained.

In addition, other semiconductor structures can also be fabricated with BGalnN materials system. As discussed above, Group-Ill nitride materials, especially GaN and AIN, are promising for use in electronic devices which can operate under high-power and high-temperature conditions -for example, microwave power FETs by using AIGaN/GaN heterostructures. However, as noted previously hereinabove, the different lattice constants of AIGaN and GaN cause the generate of significant defects, limiting the mobility of electrons in the resultant structure and the utility of such materials systems for FET use.

The present invention also substantially overcomes these limitations, in that the BGalnN/GaN material of the present invention has a lattice constant equal to GaN. As discussed hereinabove, a quaternary materials system of B^Ga n_yN, where the GaN mole fraction (x) and InN mole fraction (y) satisfy the relationships 0 <= x + y <= 1 , 1<= 1.03x + 0.88y, and x + 1.56y = 1.01 ±0.1 not only has a band gap greater than 3.3 eV, but also has a lattice constant substantially equal to GaN. This permits fabrication of semiconductor structures such as FETs which have substantially uniform atomic content distribution in the various layers. Therefore, by using an BGalnN/GaN material system in accordance with the present invention, whose GaN mole fraction, x and AIN mole fraction, y satisfy the above relationships, high-power and high-temperature transistors with low defect density can be realized.

Referring to Figure 37, there is shown therein an exemplary embodiment of a heterojunction field effect transistor(HFET) using BGalnN/GaN material in accordance with the present invention. On a GaN substrate 2520, a 0.5 μm i- ^Bo_.oι^Gao.₈₆'ⁿo.i₃ ^N '^ayer 2525 is formed, followed by a thin, approximately 10 nm i- B₀₀₁Ga₀₈₆ln_{0 13}N conducting channel layer 2530 and a 10 nm GaN layer 2535. Source and drain electrodes 2540A-B, and gate electrode 2545 are formed in a conventional manner. In the structure, the GaN mole fraction, x, and AIN mole fraction, y, of the BGalnN layer are set to be 0.86 and 013, respectively. In this case, the value of x and y satisfy the relationship of 0 <= x + y <= 1 , 1 <= 1.03x + 0.88y, and x + 1.56y = 1.01 ±0.1. This results in an BGalnN layer substantially without phase separation and with a lattice constant almost equal to GaN, In turn, this permits high electron velocities to be achieved because the two dimensional electron gas formed in the heterointerface of BGalnN and GaN layer is not scattered by any fluctuation in atomic content of the BGalnN layer (such as would be caused in the presence of defects). Moreover, the band gap of the BGalnN is larger than 3.3 eV so that reliable high-temperature operation can be achieved by using the structure shown in Figure 35A. Similarly, Figure 37B shows an embodiment of a heterojunction bipolar transistor(HBT) in accordance with the present invention. On the GaN substrate 2550, a 400 nm thick n-type GaN collector layer 2555 is formed, followed by a 50 nm thick p-type BGalnN base layer 2560, and a 300 nm thick GaN emitter layer 2565. Base electrode 2570, collector electrode 2575 and emitter electrode 2580 are formed conventionally. As with Figure 37A, for the exemplary embodiment of Figure 37B the GaN and AIN mole fractions x and y of the BGalnN layer are set to be 0.86 and 0.13, respectively, and x and y are required to satisfy the same relationships as discussed above. As with Figure 37A, an BGalnN layer without significant phase separation and with a lattice constant equal to GaN is realized, resulting in a very high quality heterojunction of BGalnN/GaN. In addition, the band gap of the GaN emitter layer (3.5 eV) is larger than that of BGalnN base layer (3.3 eV) so that holes generated in the p-type base layer are well confined in that base layer. This results because of the larger valence band discontinuity between GaN and BGalnN than would occur in a GaN homojunction bipolar transistor. This has the benefit of obtaining a large current amplification of collector current relative to base current. Moreover, as mentioned above, the bandgap of the BGalnN and the GaN layer is large so that the transistor can be used reliably in high-temperature applications. Referring next to Figure 38, there is shown therein an implementation of the present invention as a phototransistor.

B^_yGa n_yN quaternary material whose GaN mole fraction, x and AIN mole fraction, y satisfy the relationship of 0 <= x + y <= 1 , 1 <= 1.03x + 0.88y, offers not only a band gap larger than 3.2 eV, but also can be fabricated in layers with equal atomic content distribution, so that BGalnN material also can be used for blue photo detector applications. Moreover, the B^Ga n_yN quaternary material whose GaN mole fraction, x and AIN mole fraction, y satisfy the relationship of x + 1.56y = 1 has a lattice constant equal to GaN. Therefore, by using BGalnN/GaN material whose GaN mole fraction, x and AIN mole fraction, y satisfy the above relationship, blue photo detectors with low defect density can be realized. In the event that detection of other frequencies is desired, for example blue light, only slight modification is required.

As shown in Figure 38, the semiconductor device of the present invention can be implemented as a heterojunction phototransistor(HPT) using BGalnN/GaN material. On the GaN substrate 2700, an GaN collector layer 2705 is formed on the order of 500 nm thick n-type, followed by the formation of a 200 nm thick p-type BGalnN base layer 2710. Thereafter, an emitter layer 2715 on the order of 500 nm thick is formed. On the emitter layer, a ring shaped electrode 2720 is formed to permit light to impinge on the base layer. In an exemplary structure, the GaN mole fraction, x and AIN mole fraction, y of the BGalnN layer are set to be 0.86 and 0.13, respectively. In this case, the value of x and y satisfy the relationship of 0 <= x + y <= 1 , 1<= 1.03x + 0.88y, and x + 1.56y = 1.06, so that a BGalnN layer can be formed with substantially avoids phase separation while having a lattice constant almost equal to GaN, thus permitting the formation of a high quality heterojunction of BGalnN/GaN. The band gap of the GaN emitter layer (3.5 eV which corresponds to the light wavelength of 380 nm) is larger than that of BGalnN base layer (3.3eV which corresponds to the light wavelength of

5 370 nm). The light impinges on the emitter side. For the embodiment shown, impinging light in the wavelength range between 370 nm and 380 nm is transparent to the emitter layer, so that the light in that range is absorbed in the BGalnN base layer and generates electron and hole pairs. The holes generated by the optical absorption in the p-type base layer are well confined in the base layer because the valence band discontinuity between GaN and BGalnN is larger than that for a conventional GaN homojunction photo transistor. This leads to the induction of a larger emitter current, which offers better electronic neutralization in the base region than in the case of the homojunction photo transistor. Therefore, blue photo detectors with high quantum efficiency and high sensitivity, and the resultant high conversion efficiency from input light to collector current, are obtained. In the event that other lower frequencies are to be detected, the BGalnN base layer may be replaced with, for example for blue-green light, InGaN.

In addition to the phototransistor of Figure 38, it is also possible to implement a photodiode in accordance with the present invention. Referring to Figure 39, an n- type GaN substrate 1900 is provided, on which is formed an n-type layer 1910 of B^ _x._yGa_xln_yN quaternary material or equivalent, which conforms to the relationships discussed above in connection with Figure 38. An active layer 2915 is thereafter formed, and above that is formed a layer 2920 of p-type B^Ga n_yN quaternary material. Then, a p-type second cladding layer 2925 is formed above the layer 2920, and a window 2930 is formed therein to expose a portion of the layer 2920.The window 2930 provides a port by which light can impinge on the layer 2920, causing the creation of holes. A pair of electrodes 2935 and 2940 may be fabricated in a conventional manner, with the electrode 2935 typically being a ring electrode around the window 2930. It will be appreciated that the band gap of the second cladding layer 2925 is preferably larger than the band gap of the layer 2920, which is in turn preferably larger than the band gap of the active layer 2915; such an approach provides sensitivity to the widest range of wavelength of light. If the event a narrower range is desired, a material with a lower band gap than the layer 2920 may be used for the layer 2925. In addition, it is also not necessary to include the layer 2925 in all embodiments, as the layers 2910, 2915 and 2920 provide, in at least some instances, an adequate photosensitive pn-junction.

Referring next to Figure 40, a ninth embodiment of the present invention may be better appreciated. The ninth embodiment uses BlnAIN quaternary material system to provide an ultra violet light emitting device. Referring to Figure 40, shown therein in cross-sectional view is a semiconductor structure according to a ninth embodiment of the invention. A diode of the ninth embodiment with particular reference to Figure 40, an n-type AIN substrate 400 is provided and an n-type AIN first cladding layer 405 (typically 0.5μm thick) is formed thereon. Thereafter, a second cladding layer 410, typically of an n-type B₀₀₁ln₀₀₁AI₀₉₈N material which may be on the order of 1.5 μm thick, is formed thereon, followed by a multiple quantum well active layer 415 which in an exemplary arrangement may comprise three quantum well layers of B₀₀₁ln₀₀₈AI₀₉₁N material on the order of 35A thick together with four barrier layers of B₀₀₂ln₀₀₇AI₀₉₁N material on the order of 35A thick, arranged as three pairs. Next, a third cladding layer 420 of a p-type B₀₀₁ln₀₀₁AI₀₉₈N ( typically on the order of 1.5 μm thick) is formed, followed by a p-type AIN fifth cladding layer 425 (on the order of 0.5μm thick). A SiO₂ layer 430 having one stripe like window region 435 (3.0μm width) is formed on the p-type AIN fourth cladding layer 425. A first electrode 440 is formed on the n-type AIN substrate 400, while a second electrode 445 is formed on the SiO₂ layer 430 and the window region 435.

In order to emit ultra violet light with a wavelength range of 220 nm from the active layer 415, the BN mole fraction, the InN mole fraction, and the AIN mole fraction of the well layer are set to be 0.01 , 0.08, and 0.91 , respectively. To avoid defects due to lattice mismatch, the lattice constants of the various constituent layers are matched to each other by setting the InN mole fraction, x, and the AIN, y, in each of the layers to meet the condition 1.75x + y nearly equals a constant value. In an exemplary embodiment, the constant value is set to nearly 1.03, for example 1.03±0.1, although most embodiments will be in the range 1.03±0.05. By proper selection of materials, the band gap energy of the n-type second cladding layer 410 and the p-type third cladding layer 420 are larger than that of the 3 pairs of multiple quantum well active layers 415. This confines the injected carriers from the n-type second cladding layer 410 and p-type third cladding layer 420 within the active layer 415, where the carriers recombine to lead to the emission of ultra violet light. In addition, the refractive index of the n-type second cladding layer 410 and the p-type third cladding layer 420 are smaller than that of the multiple quantum well active layer 415, which confines the optical field in the transverse direction.

Because the injected current from the electrode 445 is confined to flow through the window region 435, the region in the active layer 415 under the widow region 435 is activated strongly. This causes the local modal gain in the active layer under the window region to be higher than the local modal gain in the active layer under the SiO₂ layer. Therefore, a gain guided waveguide is formed leading to lasing oscillation in the structure of the ninth embodiment. Figures 41A-41 D show, in sequence, a summary of the fabrication steps necessary to construct an exemplary laser diode according to the ninth embodiment. Since the structure which results from Figures 41 A-41 D will resemble that shown in Figure 40, like reference numerals will be used for elements whenever possible. With reference first to Figure 41A, an n-type AIN substrate 400 is provided, on which is grown an n-type AIN first cladding layer 405. The first cladding layer 405 is typically on the order of 0.5μm thick. Thereafter, an n-type B₀₀₁ln₀₀₁AI₀₉₈N second cladding layer 410 is formed, typically on the order of 1.5 μm thick.

Next, a multiple quantum well active layer 415 is formed by creating three quantum wells comprised of three layers of of B₀₀₁ln₀₀₈AI₀₉₁N material each on the order of 35A thick, together with four barrier layers of B₀₀₂ln₀₀₇AI₀₉₁N material on the order of 35A thick. A third cladding layer 420 of p-type B₀₀₁ln₀₀₁Al₀₉₈N material, on the order of 1.5 μm thick, is then formed, after which is formed a fourth cladding layer 425 of a p-type AIN on the order of 0.5μm thick. Each of the layers is typically formed by either the Metal Organic Chemical Vapor Deposition (MOCVD) method or the Molecular Beam Epitaxy (MBE) method.

Then, as shown in Figure 41 B, a silicon dioxide (SiO₂) layer 430 is formed on the p-type AIN fourth cladding layer 425, for example by the Chemical Vapor

Deposition (CVD) method. Using photolithography and etching or any other suitable method, a window region 435 is formed as shown in Figure 41 C. The window region

435 may be stripe-like in at least some embodiments. Finally, as shown in Figure

41 D, a first electrode 440 and a second electrode 445 are formed on the n-type AIN substrate 400 and on the SiO₂ layer 430, respectively, by evaporation or any other suitable process. Referring next to Figure 42, a tenth embodiment of a semiconductor structure in accordance with the present invention may be better appreciated. As with the ninth embodiment, an exemplary application of the tenth embodiment is the creation of a laser diode. The structure of the tenth embodiment permits a waveguide with a real refractive index guide to be built into the structure. This provides a low threshold current laser diode which can operate with a fundamental transverse mode.

Continuing with reference to Figure 42, for ease of reference, like elements will be indicated with like reference numerals. On an n-type AIN substrate 400, a first cladding layer 405 is formed of an n-type AIN on the order of 0.5μm thick. Successively, an n-type second cladding layer 410 is formed of B₀₀₁ln₀₀₁AI₀₉₈N material on the order of 1.5 μm thick. Thereafter, a multiple quantum well active layer 415 is formed comprising three well layers of B₀₀₁ln₀₀₈AI₀₉₁N material on the order of 35A thick together with four barrier layers of B₀₀₂l n₀₀₇AI₀₉₁ N material , also on the order of 35A thick. Next, a third, p-type cladding layer 420 formed of ^Bo.oι^lno.oι^A,o_.98N material on the order of 1.5 μm thick is formed. Thereafter, a p-type AIN fourth cladding layer 425 on the order of 0.5μm thick is formed over the ridge structure 3500 of the third cladding layer 420. The third and fourth cladding layers are then partially removed to create a ridge structure 3500. A silicon dioxide (SiO₂) layer 5 430 is then formed over the fourth cladding layer 425 as well as the remaining exposed portion of the third cladding layer 420. A window region 435, which may be stripe-like on the order of 2.0μm width, is formed through the SiO₂ layer above the fourth and third cladding layers 425 and 420, respectively. As with the ninth embodiment, a first electrode 440 is formed on the n-type AIN substrate 400 and a

10 second electrode 445 is formed on the SiO₂ layer 430 and the window region 435.

As with the ninth embodiment, in order to emit ultra violet light with a wavelength in the range of 220 nm from the active layer 415, the mole fractions of

BN, InN, and AIN in the well layer are set to be 0.01, 0.08, and 0.91, respectively.

Likewise, in order to match the lattice constants of each of the constituent layers to

15 avoid defects due to lattice mismatch, the InN mole fraction, x, and the AIN, y, of all the layers satisfy the condition of 1.75x + y nearly equals a constant value. As in the eighth embodiment, 1.75x + y set to be nearly equals 1.03 so that the equivalent lattice constants of each layers become nearly equal to the lattice constant of AIN. Likewise, the band gap energy of the cladding layers is maintained larger than the

20 band gap energy for the active layer, allowing the emission of ultraviolet light. Similarly the refractive index of the materials is as discussed in connection with the eighth embodiment, permitting the optical field to be confined in the transverse direction.

Similartothe operation of the ninth embodiment, the region of the active layer

25 415 under the window region 435 is activated strongly because of the constraints on the injected current by the SiO₂ layer. The result, again, is that the local modal gain in the active layer under the window region 435 is higher than the local modal gain in the active layer under the SiO₂ layer 430. This, combined with the relatively higher effective refractive index in the transverse direction inside the ridge stripe region 0 compared to that outside the ridge stripe region, provides an effective refractive index step (Δn). This results in a structure which has, built in, a waveguide formed by a real refractive index guide. Therefore, the design of the tenth embodiment provides a low threshold current laser diode which can operate with a fundamental transverse mode. 5 Referring next to Figures 43A-43E, a summary of the key fabrication steps is shown for an exemplary device of a semiconductor laser diode in accordance with the tenth embodiment.

Referring first to Figures 43A and 43B, the formation of the first and second cladding layers 405 and 410 on an n-type AIN substrate 400, together with the three- pair multiple quantum well active layer 415 are the same as for the eighth embodiment. Thereafter, the third and fourth cladding layers 420 and 425 are formed and then partially removed - typically by etching - to create a ridge structure 3500. As before, in an exemplary embodiment the various layers are formed successively by either the MOCVD or the MBE method.

Then, as shown in Figure 43C-43E, a silicon dioxide layer 430 is formed over the fifth and third cladding layers 425 and 420, respectively, typically by the CVD method, after which a window region 435 is formed as with the ninth embodiment. Electrodes 440 and 445 are then evaporated or otherwise bonded to the structure.

Referring next to Figure 44, the selection of the InN mole fraction, x, and the

AIN mole fraction, y, and the relationship therebetween for the constituent BlnAIN layers, may be better understood. In particular, the relative mole fractions are required to satisfy, approximately, the relationship 0 <= x + y <=1 and 1<= 1.01x + 0.88y, or 0 <= x + y <=1 and 1<= 0.61x + 1.04y.

Figure 45 shows the boundary of phase separation region plotted against various growth temperatures. The lines in Figure 45 show the boundary between the compositionally unstable (phase separation) region and stable region with respect to various temperatures. The region surrounded with the two boundary lines for the same temperature shows the phase separation content region for the each temperature. It has been discovered that the ternary alloys BAIN, BlnN, and InAIN have a large phase separation region due to the large lattice mismatch between BN and AIN, between BN and InN, and between InN and AIN. Therefore, the quaternary alloy BlnAIN has a wide phase separation region, and also each atomic content of B, Al, and In should be chosen carefully for the application of the devices.

It has been discovered that an BlnAIN material system can be provided in which the usual crystal growth temperature is in the approximate range of around 500 °C to around 1000°C like in the case of InGaAIN. Likewise, it has been discovered that phase separation of the B content, Al content, and In content of BlnAIN does not occur significantly at processing temperatures between on the order of 500 °C and on the order of 1000 °C. Finally, by combining the two, the content choice region of Al content and In content in BlnAIN to avoid phase separation at a crystal growth temperature below around 1000 °C is found to be the shadow region in Figure 45, with the line separating the two regions being approximately defined by the relationship 1.01x + 0.88y =1 and 0.61 x + 1.04y=1.

Therefore, for each of the two structural embodiments using BlnAIN disclosed hereinabove, the phase separation phenomena can be avoided in an BlnAIN material system by operating at a crystal growth temperature between on the order of 500 °C and around 1000 °C, when the In mole fraction, x, and the AIN mole fraction, y, of the all constituent layers of the laser diodes are made to satisfy approximately the relationship of 0 <= x + y <=1 and 1<= 1.01x + 0.88y, or 0 <= x + y <=1 and 1<=

0.61 x + 1.04y. The result is the substantially uniform distribution of B atoms, Al atoms, and In atoms in each constituent layer according to the atomic mole fraction.

Figure 46 shows the content choice line of In content, x, and Al content, y, in an BlnAIN system to avoid phase separation phenomenon at growth temperatures below around 1000 °C. The line in Figure 46 shows the exemplary line of 1.75x + y =

1.03. Therefore, by ensuring that the Al content and In content of the constituent BlnAIN layers of a laser diode formed on a AIN substrate have a relationship of 1.75x

+ y nearly equal to 1.03, 0 <= x + y <=1 , and 1<= 0.61 x + 1.04y, a laser diode on a

AIN substrate with low defect density and no or very little phase separation can be obtained.

In addition, other semiconductor structures can also be fabricated with BlnAIN materials system. As discussed above, Group-Ill nitride materials, especially GaN and AIN, are promising for use in electronic devices which can operate under high- power and high-temperature conditions - for example, microwave power FETs by using AIGaN/GaN heterostructures. However, as noted previously hereinabove, the different lattice constants of AIGaN and GaN cause the generation of significant defects, limiting the mobility of electrons in the resultant structure and the utility of such materials systems for FET use.

The present invention also substantially overcomes these limitations, in that the BlnAIN/AIN material of the present invention has a lattice constant equal to AIN. As discussed hereinabove, a quaternary materials system of B^ln^N, where the InN mole fraction (x) and AIN mole fraction (y) satisfy the relationships 0 <= x + y <= 1 , 1<= 0.61x + 1.04y, and 1.75x + y = 1.03±0.1 not only has a band gap greater than 5 eV, but also has a lattice constant substantially nearly equal to AIN. This permits fabrication of semiconductor structures such as FETs which have substantially uniform atomic content distribution in the various layers. Therefore, by using an BlnAIN/AIN material system in accordance with the present invention, whose InN mole fraction, x and AIN mole fraction, y satisfy the above relationships, high-power and high-temperature transistors with low defect density can be realized.

Referring to Figure 47, there is shown therein an exemplary embodiment of a heterojunction field effect transistor(HFET) using BlnAIN/AIN material in accordance with the present invention. On an AIN substrate 3520, a 0.5 μm i- ^Bo.oι^,no.o₈ ^A,o.₉iN ^layer 3525 is formed, followed by a thin, approximately 10 nm B₀₀₁ln₀₀₈AI₀₉₁N conducting channel layer 3530 and a 10 nm AIN layer 3535. Source and drain electrodes 3540A-B, and gate electrode 3545 are formed in a conventional manner. In the structure, the InN mole fraction, x, and AIN mole fraction, y, of the

BlnAIN layer are set to be 0.08 and 0.91 , respectively. In this case, the value of x and y satisfy the relationship of 0 <= x + y <= 1 , 1<= 0.61 x + 1.04y, and 1.75x + y =

1.03±0.1. This results in an BlnAIN layer substantially without phase separation and with a lattice constant almost equal to AIN, In turn, this permits high electron velocities to be achieved because the two dimensional electron gas formed in the heterointerface of BinAIN and AIN layer is not scattered by any fluctuation in atomic content of the BinAIN layer (such as would be caused in the presence of defects).

Moreover, the band gap of the BGalnN is larger than 5 eV so that reliable high- temperature operation can be achieved by using the structure shown in Figure 47A.

Similarly, Figure 47B shows an embodiment of a heterojunction bipolar transistor(HBT) in accordance with the present invention. On the AIN substrate 3550, a 400 nm thick n-type AIN collector layer 3555 is formed, followed by a 50 nm thick p-type BlnAIN base layer 3560, and a 300 nm thick AIN emitter layer 3565. Base electrode 3570, collector electrode 3575 and emitter electrode 3580 are formed conventionally. As with Figure 47A, for the exemplary embodiment of Figure 47B the

InN and AIN mole fractions x and y of the BinAIN layer are set to be 0.08 and 0.91 , respectively, and x and y are required to satisfy the same relationships as discussed above. As with Figure 47A, an BlnAIN layer without significant phase separation and with a lattice constant equal to AIN is realized, resulting in a very high quality heterojunction of BlnAIN/AIN. In addition, the band gap of the AIN emitter layer (6.2 eV) is larger than that of BlnAIN base layer (5.8 eV) so that holes generated in the p-type base layer are well confined in that base layer. This results because of the larger valence band discontinuity between AIN and BlnAIN than would occur in a AIN homojunction bipolar transistor. This has the benefit of obtaining a large current amplification of collector current relative to base current. Moreover, as mentioned above, the bandgap of the BlnAIN and the AIN layer is large so that the transistor can be used reliably in high-temperature applications.

Referring next to Figure 48, there is shown therein an implementation of the present invention as a phototransistor.

B^_yln^l_yN quaternary material whose InN mole fraction, x and AIN mole fraction, y satisfy the relationship of 0 <= x + y <= 1 , 1<= 0.61x + 1.04y, offers not only a band gap larger than 5 eV, but also can be fabricated in layers with equal atomic content distribution, so that BlnAIN material also can be used for blue photo detector applications. Moreover, the B^ln^N quaternary material whose InN mole fraction, x and AIN mole fraction, y satisfy the relationship of 1.75x + y = 1.03 has a lattice constant nearly equal to AIN. Therefore, by using BlnAIN/AIN material whose InN mole fraction, x and AIN mole fraction, y satisfy the above relationship, ultra violet photo detectors with low defect density can be realized. In the event that detection of other frequencies is desired, for example blue light, only slight modification is required.

As shown in Figure 48, the semiconductor device of the present invention can be implemented as a heterojunction phototransistor(HPT) using BlnAIN/AIN material. On the AIN substrate 3700, an AIN collector layer 3705 is formed on the order of 500 nm thick n-type, followed by the formation of a 200 nm thick p-type BinAIN base layer 3710. Thereafter, an emitter layer 3715 on the order of 500 nm thick is formed. On the emitter layer, a ring shaped electrode 3720 is formed to permit light to impinge on the base layer.

In an exemplary structure, the InN mole fraction, x, and AIN mole fraction, y, of the BinAIN layer are set to be 0.08 and 0.91 , respectively. In this case, the value of x and y satisfy the relationship of 0 <= x + y <= 1 , 1<= 0.61x + 1.04y, and 1.75x + y = 1.03±0.05 so that a BinAIN layer can be formed with substantially avoids phase separation while having a lattice constant almost equal to AIN, thus permitting the formation of a high quality heterojunction of BlnAIN/AIN. The band gap of the AIN emitter layer (6.2 eV which corresponds to the light wavelength of 200 nm) is larger than that of BlnAIN base layer (5.8 eV which corresponds to the light wavelength of 212 nm). The light impinges on the emitter side. For the embodiment shown, impinging light in the wavelength range between 200 nm and 212 nm is transparent to the emitter layer, so that the light in that range is absorbed in the BlnAIN base layer and generates electron and hole pairs. The holes generated by the optical absorption in the p-type base layer are well confined in the base layer because the valence band discontinuity between AIN and BinAIN is larger than that for a conventional AIN homojunction photo transistor. This leads to the induction of a larger emitter current, which offers better electronic neutralization in the base region than in the case of the homojunction photo transistor. Therefore, blue photo detectors with high quantum efficiency and high sensitivity, and the resultant high conversion efficiency from input light to collector current, are obtained. In the event that other lower frequencies are to be detected, the BlnAIN base layer may be replaced with, for example for blue-green light, InGaN.

In addition to the phototransistor of Figure 48, it is also possible to implement a photodiode in accordance with the present invention. Referring to Figure 49, an n- type AIN substrate 3900 is provided, on which is formed an n-type layer 3910 of B^. _yln_xAl_yN quaternary material or equivalent, which conforms to the relationships discussed above in connection with Figure 48. An active layer 3915 is thereafter formed, and above that is formed a layer 3920 of p-type B^ln^N quaternary material. Then, a p-type second cladding layer 3925 is formed above the layer 3920, and a window 3930 is formed therein to expose a portion of the layer 3920.The window 3930 provides a port by which light can impinge on the layer 3920, causing the creation of holes. A pair of electrodes 3935 and 3940 may be fabricated in a conventional manner, with the electrode 3935 typically being a ring electrode around the window 3930. It will be appreciated that the band gap of the second cladding layer 3925 is preferably larger than the band gap of the layer 3920, which is in turn preferably larger than the band gap of the active layer 3915; such an approach provides sensitivity to the widest range of wavelength of light. If the event a narrower range is desired, a material with a lower band gap than the layer 3920 may be used for the layer 3925. In addition, it is also not necessary to include the layer 3925 in all embodiments, as the layers 3910, 3915 and 3920 provide, in at least some instances, an adequate photosensitive pn-junction.

Having fully described a preferred embodiment of the invention and various alternatives, those skilled in the art will recognize, given the teachings herein, that numerous alternatives and equivalents exist which do not depart from the invention. It is therefore intended that the invention not be limited by the foregoing description, but only by the appended claims.

Claims

We claim:

1. A semiconductor structure comprising: a first cladding layer of InGaAIN material having a first conduction type, an InGaAIN active layer, and a second cladding layer of InGaAIN material having a conduction type opposite the first conduction type, the mole fractions of the constituent elements of each layer being selected to minimize phase separation.

2. A semiconductor structure comprising: a first cladding layer of InGaAIN material having a first conduction type, an InGaAIN active layer, and a second cladding layer of InGaAIN material having a conduction type opposite the first conduction type, the crystal growth temperature and the mole fractions of the constituent elements of each layer being selected to minimize phase separation.

3. A light emitting device according to claim 1 , wherein the GaN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that x + 1.2y nearly equals to a constant value.

4. A light emitting device according to claim 1 , wherein the GaN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that x + 1.2y nearly equals to 1.

5. A light emitting device comprising: a first conduction type of an InGaAIN first cladding layer without phase separation, an InGaAIN active layer without phase separation, and a second conduction type of InGaAIN second cladding layer without phase separation, said InGaAIN second cladding layer having a ridge structure, all successively formed one upon each other.

6. A light emitting device according to claim 4, wherein the GaN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that x + 1.2y nearly equals constant value.

7. A light emitting device according to claim 4, wherein the GaN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that x + 1.2y nearly equals 1.

8. A light emitting device comprising: a certain. conduction type of a GaN first cladding layer, an In^^Ga^AI^N second cladding layer of said certain conduction type, an ln₁._x2-y2Ga_x2Al_y2N active layer, an opposite conduction type of an ln_1-x3._y3Ga_x3Al_y3N third cladding layer, an opposite conduction type of GaN fourth cladding layer, all successively formed one upon each other, wherein x1 , x2, x3 define the gallium mole fraction, y1 ,y2 and y3 define the aluminum mole fraction, and x1 , y1 , x2, y2, x3 and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1 <= x1/0.80 + y1/0.89, 1<= X2/0.80 + y2/0.89, 1<= X3/0.80 + y3/0.89, and Eg_lnN(1-x1-y1) + Eg_GaNX1 ⁺ Eg_A,_Ny1 > Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg_A1Ny2, Eg_lnN(1-x3-y3) + Eg_GaNx3 ⁺ Eg_A,_Ny3 > Eg_lnN(1-x3-y3) + Eg_GaNx3 + Eg_AINy3 where Eg_lnN, Eg_GaN, and Eg_AIN are the bandgap energy of InN, GaN, and AIN, respectively.

9. A light emitting device according to claim 7, wherein said active layer is an InGaAIN single or multiple quantum well active layer whose GaN mole fraction, xw, and AIN mole fraction, yw of all the constituent layers of said active layer satisfy the relationship of 0 < xw + yw <1 and 1<= xw/0.80 + yw/0.89.

10. A light emitting device according to claim 7, wherein the condition of xs + 1.2ys nearly equals to a constant value is satisfied, wherein xs and ys are the GaN mole fraction and the AIN mole fraction, respectively in each constituent InGaAIN layers.

11. A light emitting device according to claim 7, wherein the relationship of xs +

1.2ys nearly equals 1 is satisfied, where xs and ys are the GaN mole fraction and the AIN mole fraction, respectively in each constituent InGaAIN layers.

12. A light emitting device comprising: a certain conduction type of an In^^Ga^A ^N first cladding layer of said certain conduction type, an In^^^Ga^A^N active layer, an opposite conduction type of an

second cladding layer, said ln_1-x3._y3Ga_x3Al_y3N second cladding layer has a ridge strict, all successively formed one upon each other, wherein x1 , x2, and x3 define the gallium mole fraction, y1 , y2, and y3 define the aluminum mole fraction, and x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= x1/0.80 + y1/0.89, 1<= x2/0.80 + y2/0.89, 1<= X3/0.80 + y3/0.89, Eg_lnN(1-x1-y1) + Eg_GaNx1 + Eg_AlNy1 > Eg_lnN(1-x2- y2) + Eg_GaNx2 + Eg_AINy2, and Eg_lnN(1-x3-y3) + Eg_GaNx3 + Eg^ > Eg_lnN(1-x2-y2) + Eg_GaNx2 + Eg_AINy2, where Eg_lnN, Eg_GaN, and Eg_AIN are the bandgap energy of InN, GaN, and AIN, respectively.

13. A light emitting device according to claim 11 , wherein said active layer is an InGaAIN single or multiple quantum well active layer whose GaN mole fraction, xw, and AIN mole fraction, yw of all the constituent layers satisfy the relationship of 0 < xw + yw <1 and 1<= x/0.80 + y/0.89.

10

14. A light emitting device according to claim 11 , wherein the condition of xs + 1.2ys nearly equals to a constant value is satisfied, where xs and ys are the GaN mole fraction and the AIN mole fraction, respectively in each constituent InGaAIN layers.

15

15. A light emitting device according to claim 11 , wherein the relationship of xs + 1.2ys nearly equals 1 is satisfied, wherein xs and ys are the GaN mole fraction and the AIN mole fraction, respectively in each constituent InGaAIN layers.

20 16. A photo detector device comprising: a certain conduction type of an InGaAIN collector layer without phase separation, an opposite conduction type of InGaAIN base layer without phase separation, a conduction type of said certain conduction type of InGaAIN emitter layer without phase separation, all successively formed one upon each other,

25 wherein the bandgap of said InGaAIN base layer is smaller than the other InGaAIN layers.

17. A photo detector device according to claim 16, wherein the GaN mole fraction, x, and the AIN, y, of the said constituent InGaAIN layers satisfy the 0 relationship of 0 < x + y <1 , 1 <= x/0.80 + y/0.89.

18. A photo detector device according to claim 17, wherein the GaN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that x + 1.2y nearly equals to a constant value. 5

19. A photo detector device according to claim 17, wherein the GaN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that x + 1.2y nearly equals to 1.

20. A semiconductor structure comprising: a first cladding layer of BAIGaN material having a first conduction type, an BAIGaN active layer, and a second cladding layer of BAIGaN material having a conduction type 5 opposite the first conduction type, the mole fractions of the constituent elements of each layer being selected to minimize phase separation.

21. A semiconductor structure comprising: a first cladding layer of BAIGaN material having a first conduction type, 10 an BAIGaN active layer, and a second cladding layer of BAIGaN material having a conduction type opposite the first conduction type, the crystal growth temperature and the mole fractions of the constituent elements of each layer being selected to minimize phase separation.

15

22. A light emitting device according to claim 20, wherein the AIN mole fraction, x, and the GaN, y, of all the constituent layers satisfy the condition that x + 1.12y nearly equals to a constant value.

20 23. A light emitting device according to claim 20, wherein the AIN mole fraction, x, and the GaN, y, of all the constituent layers satisfy the condition that x + 1.12y nearly equals to 1.

24. A light emitting device comprising:

25 a first conduction type of an BAIGaN first cladding layer without phase separation, an BAIGaN active layer without phase separation, and a second conduction type of BAIGaN second cladding layer without phase separation, said BAIGaN second cladding layer having a ridge structure, all successively formed one upon each other.

30

25. A light emitting device according to claim 24, wherein the AIN mole fraction, x, and the GaN, y, of all the constituent layers satisfy the condition that x + 1.12y nearly equals constant value.

35 26. A light emitting device according to claim 24, wherein the GaN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that x + 1.12y nearly equals 1.

27. A light emitting device comprising: a certain conduction type of an B^^AI^Ga^N first cladding layer, an B^_. _y2Al_x2Ga_y2N active layer, an opposite conduction type of an B.,__X3__y3Al_x3Ga_y3N third cladding layer, all successively formed one upon each other, wherein x1 , x2, x3 define the gallium mole fraction, y1 ,y2 and y3 define the aluminum mole fraction, and x1 , y1 , x2, y2, x3 and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= 1.04x1 + 1.03y1 , 1 <= 1.04x2 + 1.03y2, 1 <= 1.04x3 + 1.03y3, and Eg_BN(1-x1-y1 ) + Eg_AINx1 + Eg_GaNy1 > Eg_BN(1-x2-y2) + Eg_AINx2 + Eg_GaNy2, Eg_BN(1-x3-y3) + Eg_AlNx3 + Eg_GaNy3 > Eg_BN(1-x3-y3) + Eg_AINx3 + Eg_GaNy3 where Eg_BN, Eg_GaN, and Eg_A,_N are the bandgap energy of BN, GaN, and AIN, respectively.

28. A light emitting device according to claim 27, wherein said active layer is an BAIGaN single or multiple quantum well active layer whose AIN mole fraction, xw, and GaN mole fraction, yw of all the constituent layers of said active layer satisfy the relationship of 0 < xw + yw <1 and 1<= 1.04xw + 1.03yw.

29. A light emitting device according to claim 27, wherein the condition of xs +

1.2ys nearly equals to a constant value is satisfied, wherein xs and ys are the AIN mole fraction and the GaN mole fraction, respectively in each constituent BAIGaN layers.

30. A light emitting device according to claim 27, wherein the relationship of xs + 1.2ys nearly equals 1 is satisfied, where xs and ys are the AIN mole fraction and the GaN mole fraction, respectively in each constituent BAIGaN layers.

31. A light emitting device comprising: a certain conduction type of an B^^AI^Ga^N first cladding layer of said certain conduction type, an B^^^AI^Ga^N active layer, an opposite conduction type of an B^^_yaAI^Ga^N second cladding layer, said B^^-_jAI^Ga_yaN second cladding layer has a ridge strict, all successively formed one upon each other, wherein x1 , x2, and x3 define the gallium mole fraction, y1 , y2, and y3 define the aluminum mole fraction, and x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= 1.04x1 + 1.03y1 , 1<= 1.04x2 + 1.03y2, 1<= 1.04x3 + 1.03y3, Eg_BN(1-x1-y1) + Eg_AINx1 + Eg_GaNy1 > Eg_BN(1-x2-y2) + Eg_AINx2 + Eg_GaNy2, and Eg_BN(1-x3-y3) + Eg_AINx3 + Eg_GaNy3 > Eg_BN(1-x2-y2) + Eg_AINx2 + Eg_GaNy2, where Eg_BN, Eg^, and Eg_GaN are the bandgap energy of BN, AIN, and GaN, respectively.

32. A light emitting device according to claim 31 , wherein said active layer is an BAIGaN single or multiple quantum well active layer whose AIN mole fraction, xw, and GaN mole fraction, yw of all the constituent layers satisfy the relationship of 0 < xw + yw <1 and 1 <= 1.04xw + 1.03yw.

33. A light emitting device according to claim 31, wherein the condition of xs + 1.2ys nearly equals to a constant value is satisfied, where xs and ys are the AIN mole fraction and the GaN mole fraction, respectively in each constituent BAIGaN layers.

10

34. A light emitting device according to claim 31 , wherein the relationship of xs + 1.12ys nearly equals 1 is satisfied, wherein xs and ys are the AIN mole fraction and the GaN mole fraction, respectively in each constituent BAIGaN layers.

15 35. A photo detector device comprising: a certain conduction type of an BAIGaN collector layer without phase separation, an opposite conduction type of BAIGaN base layer without phase separation, a conduction type of said certain conduction type of BAIGaN emitter layer without phase separation, all successively formed one upon each other,

20 wherein the bandgap of said BAIGaN base layer is smaller than the other BAIGaN layers.

36. A photo detector device according to claim 35, wherein the AIN mole fraction, x, and the GaN, y, of the said constituent BAIGaN layers satisfy the

25 relationship of 0 < x + y <1 , 1 <= 1.04x + 1.03y.

37. A photo detector device according to claim 35, wherein the AIN mole fraction, x, and the GaN, y, of all the constituent layers satisfy the condition that x + 1.12y nearly equals to a constant value.

30

38. A photo detector device according to claim 35, wherein the AIN mole fraction, x, and the GaN, y, of all the constituent layers satisfy the condition that x + 1.12y nearly equals to 1.

35 39. A semiconductor structure comprising: a first cladding layer of BGalnN material having a first conduction type, an BGalnN active layer, and a second cladding layer of BGalnN material having a conduction type opposite the first conduction type, the mole fractions of the constituent elements of each layer being selected to minimize phase separation.

40. A semiconductor structure comprising:

5 a first cladding layer of BGalnN material having a first conduction type, an BGalnN active layer, and a second cladding layer of BGalnN material having a conduction type opposite the first conduction type, the crystal growth temperature and the mole fractions of the constituent elements of each layer being selected to minimize 10 phase separation.

41. A light emitting device according to claim 40, wherein the GaN mole fraction, x, and the InN, y, of all the constituent layers satisfy the condition that x + 1.56y nearly equals to a constant value.

15

42. A light emitting device according to claim 40, wherein the GaN mole fraction, x, and the InN, y, of all the constituent layers satisfy the condition that x + 1.56y nearly equals to 1.

20 43. A light emitting device comprising: a first conduction type of an BGalnN first cladding layer without phase separation, an BGalnN active layer without phase separation, and a second conduction type of BGalnN second cladding layer without phase separation, said BGalnN second cladding layer having a ridge structure, all successively formed

25 one upon each other.

44. A light emitting device according to claim 43, wherein the GaN mole fraction, x, and the InN, y, of all the constituent layers satisfy the condition that x + 1.56y nearly equals constant value.

30

45. A light emitting device according to claim 43, wherein the GaN mole fraction, x, and the InN, y, of all the constituent layers satisfy the condition that x + 1.56y nearly equals 1.

35 46. A light emitting device comprising: a certain conduction type of an B^^Ga^ln^N first cladding layer, an B^. _y2Ga_x2ln_y2N active layer, an opposite conduction type of an

third cladding layer, all successively formed one upon each other, wherein x1 , x2, x3 define the gallium mole fraction, y1 ,y2 and y3 define the aluminum mole fraction, and x1 , y1 , x2, y2, x3 and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= 1.03x1 + 0.88y1 or 1 <=0.95x1 + 1.03y1 , 1<= 1.03x2 + 0.88y2 or 1<=0.95x2 + 1.03y2, 1<= 1.03x3 + 0.88y3 or 1<=0.95x3 + 1.03y3 , 1<= 5 1.04x3 + 1.03y3, and Eg_BN(1-x1-y1) + Eg_GaNx1 + Eg_lnNy1 > Eg_BN(1-x2-y2) +

Eg_GaN 2 + Eg_lnNy2, Eg_BN(1-x3-y3) + Eg_GaNx3 + Eg_lnNy3 > Eg_BN(1-x3-y3) + Eg_GaNx3 + gm_Ny3 where Eg_BN, Eg_lnN, and Eg_GaN are the bandgap energy of BN, InN, and GaN, respectively.

10 47. A light emitting device according to claim 46, wherein said active layer is an BGalnN single or multiple quantum well active layer whose GaN mole fraction, xw, and InN mole fraction, yw of all the constituent layers of said active layer satisfy the relationship of 0 < xw + yw <1 and 1 <= 1.03xw + 0.88yw or 1 <= 0.95xw + 1.03yw.

15

48. A light emitting device according to claim 46, wherein the condition of xs + 1.56ys nearly equals to a constant value is satisfied, wherein xs and ys are the GaN mole fraction and the InN mole fraction, respectively in each constituent BGalnN layers.

20

49. A light emitting device according to claim 46, wherein the relationship of xs + 1.56ys nearly equals 1 is satisfied, where xs and ys are the GaN mole fraction and the InN mole fraction, respectively in each constituent BGalnN layers.

25 50. A light emitting device comprising: a certain conduction type of an B^^Ga^ln^N first cladding layer of said certain conduction type, an B^^^Ga^ln^N active layer, an opposite conduction type of an B^^Ga^n_y^ second cladding layer, said B₁._x3._y3Ga_x3ln_y3N second cladding layer has a ridge strict, all successively formed one upon each other,

30 wherein x1, x2, and x3 define the gallium mole fraction, y1, y2, and y3 define the aluminum mole fraction, and x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1 <= 1.03x1 + 0.88y1 or 1 <=0.95x1 + 1.03y1 , 1<= 1.03x2 + 0.88y2 or 1<=0.95x2 + 1.03y2, 1 <= 1.03x3 + 0.88y3 or 1<=0.95x3 + 1.03y3 , 1<= 1.04x3 + 1.03y3, and Eg_BN(1-x1-y1) + Eg_GaNx1 + Eg_lnNy1 5 > Eg_BN(1-x2-y2) + Eg_GaNx2 + Eg_lnNy2, Eg_BN(1-x3-y3) + Eg_GaNx3 + Eg_lnNy3 >

Eg_BN(1-x3-y3) + Eg_GaNx3 + Eg_(nNy3 where Eg_BN, Eg_(nN, and Eg_GaN are the bandgap energy of BN, InN, and GaN, respectively.

51. A light emitting device according to claim 50, wherein said active layer is an BGalnN single or multiple quantum well active layer whose GaN mole fraction, xw, and InN mole fraction, yw of all the constituent layers satisfy the relationship of 0 < xw + yw <1 and 1<= 1.03xw + 0.88yw or 1<=0.95xw + 1.01yw.

52. A light emitting device according to claim 50, wherein the condition of xs + 1.56ys nearly equals to a constant value is satisfied, where xs and ys are the GaN mole fraction and the InN mole fraction, respectively in each constituent BGalnN layers.

10

53. A light emitting device according to claim 50, wherein the relationship of xs + 1.56ys nearly equals 1 is satisfied, wherein xs and ys are the GaN mole fraction and the InN mole fraction, respectively in each constituent BGalnN layers.

15 54. A photo detector device comprising: a certain conduction type of an BGalnN collector layer without phase separation, an opposite conduction type of BGalnN base layer without phase separation, a conduction type of said certain conduction type of BGalnN emitter layer without phase separation, all successively formed one upon each other,

20 wherein the bandgap of said BGalnN base layer is smaller than the other BGalnN layers.

55. A photo detector device according to claim 54, wherein the GaN mole fraction, x, and the InN, y, of the said constituent BGalnN layers satisfy the

25 relationship of 0 < x + y <1 and 1<= 1.03x + 0.88y or 1 <=0.95x + 1.01 y.

56. A photo detector device according to claim 54, wherein the GaN mole fraction, x, and the InN, y, of all the constituent layers satisfy the condition that x + 1.56y nearly equals to a constant value.

30

57. A photo detector device according to claim 54, wherein the GaN mole fraction, x, and the InN, y, of all the constituent layers satisfy the condition that x + 1.56y nearly equals to 1.

35 58. A semiconductor structure comprising: a first cladding layer of BlnAIN material having a first conduction type, an BlnAIN active layer, and a second cladding layer of BinAIN material having a conduction type opposite the first conduction type, the mole fractions of the constituent elements of each layer being selected to minimize phase separation.

59. A semiconductor structure comprising:

5 a first cladding layer of BlnAIN material having a first conduction type, an BlnAIN active layer, and a second cladding layer of BlnAIN material having a conduction type opposite the first conduction type, the crystal growth temperature and the mole fractions of the constituent elements of each layer being selected to minimize 10 phase separation.

60. A light emitting device according to claim 59, wherein the InN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that 1.75x + y nearly equals to a constant value.

15

61. A light emitting device according to claim 59, wherein the InN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that 1.75x + y nearly equals to 1.

20 62. A light emitting device comprising: a first conduction type of an BlnAIN first cladding layer without phase separation, an BinAIN active layer without phase separation, and a second conduction type of BinAIN second cladding layer without phase separation, said BinAIN second cladding layer having a ridge structure, all successively formed

25 one upon each other.

63. A light emitting device according to claim 62, wherein the InN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that 1.75x + y nearly equals constant value.

30

64. A light emitting device according to claim 62, wherein the InN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that 1.75x + y nearly equals 1.

35 65. A light emitting device comprising: a certain conduction type of an B^^ln^A N first cladding layer, an B^. _y2ln_x2Al_y2N active layer, an opposite conduction type of an B^^ln^A^N third cladding layer, all successively formed one upon each other, wherein x1 , x2, x3 define the gallium mole fraction, y1 ,y2 and y3 define the aluminum mole fraction, and x1 , y1 , x2, y2, x3 and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= 1.01x1 + 0.88y1 or K=0.61x1 + 1.04y1 , 1<= 1.01x2 + 0.88y2 or 1<=0.61x2 + 1.04y2, 1<= 1.01x3 + 0.88y3 or 1<=0.61x3 + 1.04y3, and 5 Eg_BN(1-x1-y1 ) + Eg_lnNx1 + Eg_AINy1 > Eg_BN(1-x2-y2) + Eg_lnNx2 + Eg_AlNy2, Eg_BN(1-x3- y3) + Eg_lnNx3 + Eg_AINy3 > Eg_BN(1-x3-y3) + Eg_lnNx3 + Eg_AINy3 where Eg_BN, Eg_lnN, and Eg_A,_N are the bandgap energy of BN, InN, and AIN, respectively.

66. A light emitting device according to claim 65, wherein said active layer is an 10 BinAIN single or multiple quantum well active layer whose InN mole fraction, xw, and AIN mole fraction, yw of all the constituent layers of said active layer satisfy the relationship of 0 < xw + yw <1 and 1<= 1.01xw + 0.88yw or 1<= 0.61 xw + 1.04yw.

15 67. A light emitting device according to claim 65, wherein the condition of 1.75xs + ys nearly equals to a constant value is satisfied, wherein xs and ys are the InN mole fraction and the AIN mole fraction, respectively in each constituent BinAIN layers.

20 68. A light emitting device according to claim 65, wherein the relationship of 1.75xs + ys nearly equals 1 is satisfied, where xs and ys are the InN mole fraction and the AIN mole fraction, respectively in each constituent BlnAIN layers.

69. A light emitting device comprising: 5 a certain conduction type of an B^^ln^AI^N first cladding layer of said certain conduction type, an B₁__x2__y2ln_x2Al_y2N active layer, an opposite conduction type of an B^^ln^A^N second cladding layer, said B₁._x3._y3ln_x3Al_y3N second cladding layer has a ridge structure, all successively formed one upon each other, wherein x1 , x2, and x3 define the gallium mole fraction, y1 , y2, and y3 define the 0 aluminum mole fraction, and x1 , y1 , x2, y2, x3, and y3 have a relationship of 0 <= x1 + y1 <=1 , 0 < x2 + y2 <1 , 0 <= x3 + y3 <=1 , 1<= 1.01x1 + 0.88y1 or 1<=0.61x1 + 1.04y1 , 1<= 1.01x2 + 0.88y2 or 1<=0.61x2 + 1.04y2, 1<= 1.01x3 + 0.88y3 or 1<=0.61x3 + 1.04y3, and Eg_BN(1-x1-y1 ) + Eg_lnNx1 + Eg_AINy1 > Eg_BN(1-x2-y2) + Eg_lnNx2 + Eg_AINy2, Eg_BN(1-x3-y3) + Eg_lnNx3 + Eg_AINy3 > Eg_BN(1-x3-y3) + Eg_lnNx3 + 5 Eg_A,_Ny3 where Eg_BN, Eg_lnN, and Eg^ are the bandgap energy of BN, InN, and AIN, respectively.

70. A light emitting device according to claim 59, wherein said active layer is an BlnAIN single or multiple quantum well active layer whose InN mole fraction, xw, and AIN mole fraction, yw of all the constituent layers satisfy the relationship of 0 < xw + yw <1 and 1<= 1.01xw + 0.88yw or 1<=0.61xw + 1.04yw.

5 71. A light emitting device according to claim 59, wherein the condition of 1.75xs + ys nearly equals to a constant value is satisfied, where xs and ys are the InN mole fraction and the AIN mole fraction, respectively in each constituent BinAIN layers.

72. A light emitting device according to claim 59, wherein the relationship of 10 1.75xs + ys nearly equals 1 is satisfied, wherein xs and ys are the InN mole fraction and the AIN mole fraction, respectively in each constituent BlnAIN layers.

73. A photo detector device comprising: a certain conduction type of an BlnAIN collector layer without phase separation, 15 an opposite conduction type of BinAIN base layer without phase separation, a conduction type of said certain conduction type of BlnAIN emitter layer without phase separation, all successively formed one upon each other, wherein the bandgap of said BlnAIN base layer is smaller than the other BinAIN layers.

20 74. A photo detector device according to claim 73, wherein the InN mole fraction, x, and the AIN, y, of the said constituent BinAIN layers satisfy the relationship of 0 < x + y <1 and 1<= 1.01x + 0.88y or 1<=0.61x + 1.04y.

75. A photo detector device according to claim 73, wherein the InN mole 5 fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that 1.75x + y nearly equals to a constant value.

76. A photo detector device according to claim 73, wherein the InN mole fraction, x, and the AIN, y, of all the constituent layers satisfy the condition that 0 1.75x + y nearly equals to 1.

77. A semiconductor structure comprising: a first cladding layer of a B₁__x__y_₂ln_xGa_yAl_zN material having a first conduction type, 5 an B₁__x._y._zln_xGa_yAI₂N active layer, and a second cladding layer of B₁__x__y_₂ln_xGa_yAI₂,N material having a conduction type opposite the first conduction type, the mole fractions of the constituent elements of each layer being selected to minimize phase separation.

78. The semiconductor structure of claim 77 where x equals zero.

79. The semiconductor structure of claim 77 where y equals zero.

80. The semiconductor structure of claim 77 where z equals zero.

81. The semiconductor structure of claim 77 where x + y + z equals one.

82. The semiconductor structure comprising a first cladding layer of a B₁__x__y._zln_xGa_yAl_zN material having a first conduction type, an B₁__x__y__zln_xGa_yAl_zN active layer where either one of x, y or z equals zero or the sum of x, y and z equals one, and a second cladding layer of B^Jn_χGa_yA N material having a conduction type opposite the first conduction type, where either at least one of x, y or z equal zero or the sum of x, y and z equals one, the mole fractions of the constituent elements of each layer being selected to minimize phase separation.