WO2001043185A1

WO2001043185A1 - Method of fabricating an optoelectronic device

Info

Publication number: WO2001043185A1
Application number: PCT/EP2000/012308
Authority: WO
Inventors: Andreas Eberhard PLÖSSL
Original assignee: MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V.
Priority date: 1999-12-08
Filing date: 2000-12-06
Publication date: 2001-06-14
Also published as: DE19959182A1

Abstract

A method of fabricating a substrate suitable for the growth of a sequence of epitaxial layers thereon for the production of an optoelectronic device, wherein said sequence of layers has a first lattice constant and said substrate has a substrate lattice constant equal to or slightly different from said first lattice constant is characterised by the steps of selecting an auxiliary substrate (e.g. GaAs wafer) having a lattice equal to or slightly different from said first lattice constant and suitable for the growth of said epitaxial layers thereon, of bonding said auxiliary substrate onto a support substrate (for example GaP), having at least one desirable physical property but a lattice constant different from said first lattice constant, for example a support substrate transparent for the radiation of interest in the optoelectronic device, and of reducing the thickness of said auxialiary substrate to a smaller value. In an alternative, an epitaxial layer having a desired lattice constant for growth of the layer sequence of the desired optoelectronic device is grown onto the auxiliary substrate and, after bonding to the support substrate, the auxiliary substrate is fully removed.

Description

METHOD OF FABRICATING AN OPTOELECTRONIC DEVICE

The present invention relates to a method of fabricating a substrate suitable for the growth of epitaxial layers thereon, to a substrate and to an optoelectronic device.

In the fabrication process of optoelectronic devices, it is difficult, if not impossible, to select a substrate from materials generally available which would fulfil all of the requirements. Frequently, optoelectronic devices are made from epitaxial layers. Epitaxy necessitates a substrate whose crystal lattice provides a matching template for the growth of the layers comprising the optoelectronic device. To ensure good manufacturability, the material should be of sufficient mechanical rigidity and of good availability. On the other hand, the efficient operation of the device, presupposes certain optical, electronic or thermal properties. Thus, for the fabrication of optoelectronic devices such as light emitting diodes or lasers including vertical cavity surface emitting lasers (VSELs), based on III-V compound semiconductors or semiconducting III-V alloys, several, potentially conflicting requirements are placed on the substrate. For the deposition of the crys- talline layers, a growth template of suitable crystallographic structure is required to permit epitaxy. On the other hand, the substrate should be a good conductor of electricity so that the device can be contacted through the substrate. Furthermore, for heat sinking, good thermal conductivity is required of the substrate. The overall efficiency of the device is particularly critical, it is compromised if the generated photons are absorbed by the substrate, which is thus highly undesirable.

For instance, in the alloy system InGaAIP, when lattice -matched to gal- Hum arsenide, direct band gap semiconducting layers can be deposited with the bandgap taking any value in the red to orange part of the visible spectrum. Light-emitting diodes of this alloy system, therefore, are grown on a substrate whose bandgap is smaller than that of the active layers, and consequently part of the photons generated in the active layer will be absorbed in the gallium arsenide substrate. One approach to keep the heteroepitaxial material system and nevertheless avoid the absorption due to a substrate being opaque in the spectral range of the active layers uses gallium arsenide only as a temporary growth template. After deposition of the layer system comprising the LEDs, the substrate is etched away and a transparent substrate is attached in its place through wafer direct bonding (see items [1- 19] of the attached list). In this way one can retain the advantages of the well developed InGaAIP epitaxial technology without losing a significant part of the generated photons due to substrate absorption.

Typically, a thick transparent layer is deposited on top of the LED prior to etching and bonding, not least in order to provide the film structure with sufficient rigidity for the subsequent handling of the detached structure.

Direct bonding usually requires very smooth and flat surfaces [20]. Thick deposited layers, however, often are often plagued by roughness and the mismatch in thermal expansion between substrate and layer can cause substantial bowing. Both difficulties can be overcome by bonding under applied mechanical pressure. However, from the viewpoint of manufac- turability and yield, a process avoiding application of pressure during bonding would be highly desirable. It is generally acknowledged as difficult to apply uniaxial pressure evenly over large areas. Uneven pressure application may cause plastic deformation or fracture. In particular, the avoidance of the bonding step after deposition of the active layers could amount to a significant simplification of the fabrication process and potential yield improvement. Surface smoothing with mechanical pressure implies deformation of the asperities causing the roughness, and in most cases this will be plastic deformation. This in turn can damage the active layers.

It is the object of the present invention to provide methods of fabricating a substrate and substrates which can be realised simply with existing technology and which overcome the above described difficulties and the problems of conflicting requirements.

In order to satisfy this object there are provided the methods, substrates and optoelectronic devices set forth in the attached claims and described in the specification.

More specifically, in accordance with a first variant of the invention, there is provided a method of fabricating a substrate suitable for the growth of a sequence of epitaxial layers thereon for the production of an optoelectronic device, wherein said sequence of layers has a first lattice constant and said substrate has a substrate lattice constant equal to or slightly different from said first lattice constant, the method being characterised by the fol- lowing steps:

a) selecting an auxiliary substrate (e.g. GaAs wafer) having a lattice constant equal to or slightly different from said first lattice constant and suitable for the growth of said epitaxial layers thereon, b) bonding said auxiliary substrate onto a support substrate (for example GaP), having at least one desirable physical property but a lattice constant different from said first lattice constant, for example a support substrate transparent for the radiation of interest in the optoelectronic device and

c) reducing the thickness of said auxiliary substrate to a smaller value.

In accordance with a second variant of the invention there is provided a method of fabricating a substrate suitable for the growth of a sequence of epitaxial layers thereon for the production of an optoelectronic device, wherein said sequence of layers has a first lattice constant and said substrate has a substrate lattice constant equal to or slightly different from said first lattice constant, the method being characterised by the following steps:

a) selecting an auxiliary substrate (e.g. GaAs wafer) having a lattice equal to or slightly different from said first lattice constant and suit- able for the growth of said epitaxial layers thereon,

b) growing at least one epitaxial layer (for example AlGalnP) onto said auxiliary substrate, said at least one epitaxial layer having a lattice constant equal to said first lattice constant or slightly different from said first lattice constant, and suitable for growth of said sequence of epitaxial layers thereon,

c) bonding said auxiliary substrate having said at least one epitaxial layer onto a support substrate (for example GaP), having at least one desirable physical property but a lattice constant different from said first lattice consta. t (for example a support substrate transparent for the radiation of interest in the optoelectronic device), and

d) removing said auxiliary substrate to leave said at least one epitaxial layer bonded to said support substrate.

Thus, the present invention decouples the various requirements placed on the ideal optoelectronic epitaxy substrate through a special combined layer substrate. A layer of suitable lattice constant, to serve as growth template, is attached to a substrate of suitable optical, electronic, thermal, or mechanical properties, so that the combined substrate meets the overall requirements placed on the substrate for the optoelectronic device. The layer or layers are attached to the substrate through wafer direct bonding. The layers themselves can be taken from bulk crystals or grown epitaxi- ally. The layers can be detached from their substrate through etching or ion beam induced exfoliation or through a combination of both techniques. The bulk of this composite substrate need not be of single crystalline structure, it can be a sintered, polycrystalline or amorphous wafer.

In keeping with the above example, a first simple implementation of the invention could be realised through a very thin gallium arsenide layer as growth template on a transparent substrate. In addition to transparency, high thermal and electrical conductivity would be a most important desideratum so that this substrate can be used for heat sinking and, electri- cally contacted at its rear side, for current contact and as a current spreading layer. One possible choice of material for the transparent substrate therefore is gallium phosphide which may be doped to achieve sufficient electrical conduction. Hydrogen implantation into gallium arsenide before bonding to gallium phosphide allows good control over the final thickness of the gallium arsenide layer after splitting (see, for example, US-PS 5,877 070 and PCT/EP99/07230), with layer thicknesses much thinner than 100 nm becoming impractical. The disadvantage of this simple approach is the residual absorption caused by the thin (ca. 100 nm) gallium arsenide layer. Thinner layers could be realised through a combination of epitaxy and ion beam induced exfoliation. A thin gallium arsenide layer can also be deposited onto an etch-stop layer. One possibility is to transfer the etch- stop and gallium arsenide layers on the gallium arsenide substrate to a suitable substrate, say gallium phosphide, for in- stance through bonding and ion beam induced exfoliation. Subsequent etching and removal of the etch-stop layer would leave a very thin layer of gallium arsenide (ca. 10 nm). This would reduce the absorption problem but not eliminate it.

For the example of GaAs on GaP and photons of 500 nm wavelength, corresponding to 2 -5 eV energy, a 10 nm GaAs layer would absorb about 10 % on normal transit. For 600 nm (2 eV) light, a 25 nm GaAs layer would also absorb about 10 % on normal transit.

A more preferable approach would not transfer a thin gallium arsenide layer onto a suitable substrate, for instance gallium phosphide, but a lattice-matched compound semiconductor layer grown on gallium arsenide such that its bandgap ensures transparency in the relevant spectral range. The layer could be an essentially lattice-matched direct or, prefera- bly, indirect semiconductor. For instance, the layer could be taken from the InGaAIP alloy system or Al lnP system. Hydrogen implantation before bonding allows transfer of the thin layer without sacrificing the original gallium arsenide wafer. Alternatively, a simple etch-stop approach and removal of the gallium arsenide layer could be used as well. If the trans- parent layer is grown thick enough, the splitting could also take place in the transparent layer.

The very same idea for a layered epitaxy substrate could also be based on a lattice constant different from the conventional gallium arsenide based alloy technology. Within the example of the AlGalnP-based light emitting diodes, germanium could be a suitable substrate. The deposition of the optoelectronically active layers must then be adjusted to the different lattice constant. Using a different lattice constant opens an additional degree of freedom in the bandgap adjustment via hetero-epitaxial synthesis. Or, as only thin layers are required, strained lattice-mismatched alloys like GaAlP on GaAs could be used.

The substrate onto which the crystalline growth template is to be trans- ferred can be a sintered or polycrystalline or single crystalline wafer of a material with suitable optical transparency, adequate electrical conductivity and sufficient thermal conductivity. The substrate may be less brittle than the single crystal conventionally used, thus reducing the risk of fracture during fabrication. The rear side of the substrate may be flat or structured.

In the case of light emitting diodes, the use of a non-monocrystailine sample can make dicing through cleavage difficult. However, sawing of the backside of the transparent substrate may allow formation of pyramidal structures with additional improvement in light output [21].

The present invention will be explained in further detail with reference to specific examples as illustrated in the drawings, which show: Fig. 1 a diagram illustrating the band gap (in electron volts) and wave lengths (in μm) of light emitting diodes based on III-V compositional semiconductors with reference to the lattice constants (in

A),

Fig. 2 a series of sketches showing a basic principle of substrate fabrication in accordance with the invention,

Fig. 3 a series of sketches illustrating one way of realising the basic principle of substrate fabrication in accordance with Fig. 2,

Fig. 4 a series of sketches illustrating a further way of realising the principle of substrate fabrication illustrated in Fig. 2,

Fig. 5 a series of sketches illustrating a preferred way of manufacturing a substrate in accordance with the invention,

Fig. 6 a series of sketches illustrating a second preferred way of realising a substrate in accordance with the present invention,

Fig. 7 a series of sketches indicating a further way of realising a substrate in accordance with the present invention, and

Fig. 8 examples of two substrates manufactured in accordance with the present invention.

Turning first to Fig. 1 , it can be seen that a GaAs substrate has a band gap of about 1.40 eV, and a lattice constant of about 5.65 A.

Moreover, from the diagram it can be seen, that for any desired band gap in the red to orange spectrum AlInGaP alloy compositions can be found so as to cover a continuous range of lattice constants. Conversely, it can be seen, exemplified by the vertical dotted line, that for a given lattice constant, here that of GaAs, AlInGaP alloy compositions exist which cover a continuous range of band gap energies from about 1.90 to about 2.35 eV in the example given. This range corresponds to that of red light.

It will appreciated that because the band gap of GaAs is substantially lower than the band gap of AlInGaP, light with an energy in the range of 1.90 to 2.35 will be readily absorbed by the GaAs and thus reduce the light yield from a diode made of AlInGaP.

The diagram of Fig. 1 also shows direct and indirect band gaps for other compositional semiconductor materials of the class III-V.

The intention of the present invention is to provide a substrate having a lattice constant equal to that of GaAs, or fairly close to it, which can be used for the epitaxial growth of a sequence of epitaxial layers necessary to realise an optoelectronic device, but without substantial absorption of light by the substrate, and with the substrate having other desirable prop- erties for the realisation of the optoelectronic device, such as high conductivity, mechanical support and adequate thermal conductivity. Various ways in which this may be done are illustrated in Figs. 2 to 7, the labelling of which makes their content basically self-explanatory.

In Fig. 2 an auxiliary substrate 10, such as GaAS, is bonded to a support substrate 12, such as GaP, and the resulting bonded substrate 14 is treated to thin the layer of the GaAs substrate 10, so that a thinned layer 10' of, for example, about 10 nm thickness is left supported on the GaP substrate. This GaAs layer 10' is a suitable template for the epitaxial growth of a layer sequence necessary to realise an optoelectronic device, such as a light emitting diode. That is to say, the thinned GaAs layer 10' has a lattice constant corresponding to that of the epitaxial layers to be grown onto it (not shown in Fig. 2). The thin nature of the GaAs layer 10' means that relatively little light will be lost in it, say about 10 % of any light passing through it. The support substrate 12 of GaP has a lattice constant different from that of GaAs, and will thus be unsuitable for the growth of the layer sequence on it. However, it has the mechanical, optical and electrical properties necessary for a substrate for an optoelectronic device, such as a light emitting diode.

Fig. 3 is basically similar to Fig. 2, but explains that the thinning of the substrate 10 to produce the thinned substrate layer 10' can take place by mechanical means, by chemo-mechanical means, by plasma-chemical means or the like.

Fig. 4 is again similar to Fig. 2, but shows a preferred embodiment of this variant of the invention, in which hydrogen ions 16 are implanted into the

GaAs substrate 10 to produce a concentration of hydrogen ions 18 at a level within the GaAs substrate 10 prior to bonding, so that, after bonding the substrate 10 with the substrate 12 to form the bonded substrate 14, the substrate 10 can be split at the level of the hydrogen ions 18 to result in the thin layer 10' shown in the diagram at the right hand side of Fig. 4. The splitting can be induced thermally or mechanically. If necessary, the split surface can be smoothed, through polishing or by surface diffusion or etching. This embodiment has the advantage that the remainder of the substrate wafer 10 can be used to produce further thin template layers 10' on further support substrates. Figs. 5 to 7 show three alternatives for realising a suitable growth template for epitaxial deposition of a layer sequence to realise an optoelectronic device, with the methods of Figs. 5 to 7 using an auxiliary GaAs substrate 10 as before, but completely dispensing with this auxiliary sub- strate prior to growth of the layer sequence.

Thus, in the example of Fig. 5, an epitaxial layer or layers 20 is first grown on the substrate 10 and thus has the same lattice constant as the substrate 10. This epitaxial layer or these epitaxial layers can, for example, consist of InGaAIP. After the growth of the epitaxial layer or layers 20, the substrate 10 is bonded to the substrate 12, so that the epitaxial layer or layers are sandwiched between the substrate 12 and the substrate 10 in the bonded structure 14, i.e. the wafer bonding takes place between the free surface of the epitaxial layer or layers and the substrate 12.

Thereafter, the GaAs layer is removed completely, for example by etching or other means, so that only the epitaxial layer or layers 20 having the desired lattice constant is present on the support substrate 12 having a different lattice constant. The layer or layers 20 consisting of InGaAIP are transparent for red light, thus virtually no light loss occurs when an optoelectronic device such as a red light emitting diode is grown onto the exposed surface of the layer or layers 20.

In Fig. 6 an etch stop layer 22 is first grown on the substrate 10 prior to the growth of the epitaxial layer or layers 20 and prior to bonding to the support substrate 12. The bonded structure 14 can then be subjected to etching to remove the GaAs substrate 10 down to the etch stop layer. The desired layer sequence for the optoelectronic device can then be grown on top of the etch stop layer 22. As an alternative, the etch stop layer can also be removed by changing to a suitable etching composition, so that, as shown at the extreme right in Fig. 6, the exposed surface of the layer or layers 20 is then used for the epitaxial growth of the desired optoelectronic device. Clearly, the lattice constant for the etch stop layer is preferably the same as or closely similar to that of the GaAs substrate 10 and that of the epitaxial layer grown thereon.

In Fig. 7, in the top row of the sketches, hydrogen ions 16 are again implanted into the substrate 10 before growth of the epitaxial layer or layers 20 thereon, which results in the structure at the right of the top row. After wafer bonding to the support substrate 12, the bonded structure results as shown at 22. The GaAs layer 10 can then be split at the level of the hydrogen ion "layer" and the residual material of the GaAs substrate 10, i.e. between the hydrogen ion layer and the epitaxial layer 20, is removed, for example by etching.

As shown at the extreme right in Fig. 7, this results in the finished structure 24 and exposes a surface of the epitaxial layer or layers 20 which can be used for growth of the optoelectronic device, with the epitaxial layer or layers 20 again being supported by the support substrate 12. As an alternative, shown in the middle row, the epitaxial layers 20 could first be grown onto the substrate 10, and ion implantation then carried out, so that one again produces a structure corresponding to the right hand structure 24 in Fig. 7, which is again bonded to the support substrate 12.

As a further alternative, shown in the bottom row of Fig. 7, the ion implantation can be carried out in such a way that the ion "layer" 18 is not provided in the substrate 10 but rather in the epitaxial layer or layers 20. After wafer bonding and splitting at the implanted hydrogen ion layer, the substrate 10 together w th part of the epitaxial layers 20 is removed in one step so that no residual part of the auxiliary substrate 10 needs to be removed by etching. The resulting structure again corresponds to 24 in Fig. 7.

Finally, Fig. 8 shows two typical examples of substrates produced in accordance with the invention which are suitable for the growth of a layer sequence to form optoelectronic devices. In the example 1 of Fig. 8, the layer sequence would be grown on the top of the thin GaAs layer, and in the example 2 it would be grown on the exposed surface of the InGaAIP layer.

It is, however, not essential to use GaAs as the auxiliary substrate. Instead, one could, for example, use a readily available Ge substrate. As was pointed out above, slight alteration of the alloy composition permits the adjustment of the lattice constant of the layers of the optoelectronic device. Here, the lattice constant is slightly different from that typically used for the layer sequence of the optoelectronic device. On the other hand, the slight difference can be a positive advantage since now strained layer de- vices can be grown which can have beneficial properties. A limit to the degree of mismatch of the lattice constant is reached when crystal defects arise which prevent the growth of the layer sequence of epitaxial layers in a quality necessary to realise an efficient optoelectronic device.

It will be appreciated that the invention is of general applicability and can be used in any circumstance when a substrate must be specifically made for a particular application and is not available as a standard wafer. That is to say, the invention is not restricted to III-IV matrix systems. Although the expitaxial structure of the semiconductor layers forming the respectively desired optoelectronic device will normally be grown on the epitaxial surface of the epitaxial layer(s) 20, it is naturally possible for at least one layer of the optoelectronic device to be incorporated in the epi- taxial layer(s) 20.

References

[1] F. A. Kish, D. A. DeFevere, D. A. Vanderwater, G. R. Trott, R. J. Weiss, and J. S. Major Jr., "High luminous flux semiconductor wafer-bonded AlGalnP/GaP large-area emitters", Electron. Lett, vol. 30, pp. 1790- 1792, 1994.

[2] F. A. Kish, F. M. Steranka, D. C. DeFevere, D. A. Vanderwater, K. G. Park, C. P. Kuo, T. D. Osentowski, M. J. Peanasky, J. G. Yu, R. M. Fletcher, D. A. Steigerwald, M. G. Craford, and V. M. Robbins, "Very high-efficiency semiconductor wafer-bonded transparent-substrate (AlxGa_1-x)o 5lno 5P/GaP light-emitting diodes", Appl. Phys. Lett., vol. 64, pp. 2839-2841 , 1994.

[3] D. A. Vanderwater, I.-H. Tan, G. E. Hofler, D. C. Defevere, and F. A. Kish, "High-brightness AlGalnP light emitting diodes", Proc. IEEE, vol. 85, pp. 1752- 1764, 1997.

[4] G. E. Hofler, D. A. Vanderwater, D. C. DeFevere, F. A. Kish, M. D. Camras, F. M. Steranka, and I.-H. Tan, "Wafer bonding of 50-mm diameter GaP to AlGalnP-GaP light-emitting diode wafers", Appl. Phys. Lett, vol. 69, pp. 803-805, 1996.

[5] D. A. Vanderwater, F. A. Kish, M. J. Peansky, and S. J. Rosner,

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[6] F. A. Kish, D. A. Vanderwater, D. C. DeFevere, D. A. Steigerwald, G. E. Hofler, K. G. Park, and F. M. Steranka, "Highly reliable and efficient semiconductor wafer-bonded AlGalnP/GaP light-emitting diodes", Electron. Lett, vol. 32, pp. 132- 134, 1996. [7] F. A. Kish and R. M. Fletcher, "AlGalnP Light-emitting diodes," in High Bήghtness Light Emitting Diodes, G. B. Stringfellow and M. G. Craford, Eds. Semiconductor and Semimetals, 48, R. K. Willardson and E. R. Weber, Eds. San Diego: Academic Press, 1997, ch. 5, pp. 149-226. [8] N. F. Gardner, H. C. Chui, E. I. Chen, M. R. Krames, J.-W. Huang, F. A. Kish, S. A. Stockman, C. P. Kocot, T. S. Tan, and N. Moll, " 1.4* efficiency improvement in transparent-substrate (Al_xGaι_-x)o.5lno.5P light- emitting diodes with thin (< 2000 A) active regions", Appl. Phys. Lett, vol. 74, pp. 2230-2232, 1999. [9] G. E. Hofler, C. Carter-Coman, M. R. Krames, N. F. Gardner, F. A. Kish, T. S. Tan, B. Loh, J. Posselt, D. Collins, and G. Sasser, "High-flux high- efficiency transparent- substrate AlGalnP/GaP light-emitting diodes", Electron. Lett, vol. 34, pp. 1781- 1782, 1998.

[10] M. R. Krames, M. Ochiai-Holcomb, G. E. Hofler, C. Carter-Coman, E. I. Chen, I.-H. Tan, P. Grillot, N. F. Gardner, H. C. Chui, J.-W. Huang, S. A. Stockman, F. A. Kish, M. G. Craford, T. S. Tan, C. P. Kocot, M. Hueschen, J. Posselt, B. Loh, G. Sasser, and D. Collins, "High-power truncated-inverted-pyramid (Al_xGaι-χ)o.5lno.5P/GaP light-emitting diodes exhibiting >50% external quantum efficiency", Appl. Phys. Lett, vol. 75, pp. 2365-2367, 1999.

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Company (Palo Alto, CA), United States Patent 5,661 ,316, 1997. [14] F. A. Kish Jr. and R. P. Schneider Jr., "Transparent substrate vertical cavity surface emitting lasers fabricated by semiconductor wafer bonding," to Hewlett-Packard Company (Palo Alto, CA), United States

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Claims

Patent Claims

1. Method of fabricating a substrate ( 14) suitable for the growth of a sequence of epitaxial layers thereon for the production of an optoelectronic device, wherein said sequence of layers has a first lattice constant and said substrate (14) has a substrate lattice constant equal to or slightly different from said first lattice constant, the method being characterised by the following steps:

a) selecting an auxiliary substrate ( 10) (e.g. GaAs wafer) having a lattice equal to or slightly different from said first lattice con- stant and suitable for the growth of said epitaxial layers thereon,

b) bonding said auxiliary substrate onto a support substrate (12) (for example GaP), having at least one desirable physical prop- erty but a lattice constant different from said first lattice constant, for example a support substrate transparent for the radiation of interest in the optoelectronic device,

c) reducing the thickness of said auxiliary substrate (10) to a smaller value.

2. Method in accordance with claim 1 and comprising the further step of implanting hydrogen ions (16) into said auxiliary substrate at a level (18) at least substantially corresponding to said smaller value, then effecting step b) and subsequently reducing the thickness of said auxiliary substrate by splitting it at the level (18) of said implanted hydrogen ions.

Method of fabricating a substrate suitable for the growth of a sequence of epitaxial layers thereon for the production of an optoelectronic device, wherein said sequence of layers has a first lattice constant and said substrate has a substrate lattice constant equal to or slightly different from said first lattice constant, the method being characterised by the following steps:

a) selecting an auxiliary substrate (10) (e.g. GaAs wafer) having a lattice equal to or slightly different from said first lattice constant and suitable for the growth of said epitaxial layers thereon,

b) growing at least one epitaxial layer (20) (for example AlGalnP) onto said auxiliary substrate, said at least one epitaxial layer having a lattice constant equal to said first lattice constant or slightly different from said first lattice constant, and suitable for growth of said sequence of epitaxial layers thereon,

c) bonding said auxiliary substrate ( 10) having said at least one epitaxial layer (20) onto a support substrate (12) (for example GaP), having at least one desirable physical property but a lattice constant different from said first lattice constant (for example a support substrate transparent for the radiation of interest in the optoelectronic device), and

d) removing said auxiliary substrate (10) to leave said at least one epitaxial layer (20) bonded to said support substrate (12).

4. Method according to claim 3, wherein said at least one epitaxial layer (20) comprises an etch stop layer (22) and one or more further epitaxial layers and wherein said auxiliary substrate (10) is removed at least partly by etching following step b) .

5. Method according to claim 4, wherein said etch stop layer (22) is subsequently removed by further etching.

6. Method according to claim 3, and comprising the further step of implanting hydrogen ions (16) into said auxiliary substrate (10) at a level (18) at least substantially corresponding to said smaller value, then effecting steps b) and c) and subsequently reducing the thickness of said auxiliary substrate (10) by splitting it at the level of said implanted hydrogen ions.

7. Method according to claim 6, wherein a residual portion of said auxiliary substrate (10) bonded via said at least one epitaxial layer (20) to said support substrate (12) is subsequently removed, for ex- ample by etching.

8. Method in accordance with any one of the preceding claims, comprising the further step of growing a sequence of epitaxial layers for the production of an optoelectronic device on either an exposed surface of said auxiliary substrate (10) of reduced thickness or on an exposed surface of said at least one epitaxial layer (20).

9. Substrate (14; 24) for the growth of a sequence of epitaxial layers to form an optoelectronic device, said substrate having been manu- factured in accordance with a method in accordance with any one of the claims 1 to 7.

10. Optoelectronic device comprising a sequence of epitaxial layers grown on a substrate (14; 24) manufactured in accordance with a method in accordance with any one of the claims 1 to 7.