A double heterostructure for a light emitting diode comprises a layer of aluminum gallium nitride having a first conductivity type; a layer of aluminum gallium nitride having the opposite conductivity type; and an active layer of gallium nitride between the aluminum gallium nitride layers,...http://www.google.com.au/patents/US5739554?utm_source=gb-gplus-sharePatent US5739554 - Double heterojunction light emitting diode with gallium nitride active layer 
