Light emitting devices having dislocation density maintaining buffer layers

Abstract

A method for forming a light emitting device comprises forming a buffer layer having a plurality of layers comprising a substrate, an aluminum gallium nitride layer adjacent to the substrate, and a gallium nitride layer adjacent to the aluminum gallium nitride layer. During the formation of each of the plurality of layers, one or more process parameters are selected such that an individual layer of the plurality of layers is strained.

What is claimed is: 
     
         1 . A light emitting device comprising:
 a silicon substrate;   a device stack comprising:
 an n-type layer, 
 a p-type layer, 
 an active layer between the n-type layer and the p-type layer; and 
 a compressive strained buffer layer between the substrate and the device stack, the buffer layer comprising:
 a tensile strained AlN layer adjacent the substrate, 
 a compressive strained GaN layer adjacent the n-type layer; and 
 a compressive strained AlGaN layer between the compressive strained GaN layer and the tensile strained AlN layer, wherein the compressive strained GaN layer is thicker than the compressive strained AlGaN layer, and the compressive strained AlGaN layer is thicker than the tensile strained AlN layer. 
 
   
     
     
         2 . The light emitting device of  claim 1 , wherein at least one of the n-type layer and the p-type layer is a Group III-V layer. 
     
     
         3 . The light emitting device of  claim 1 , wherein the thickness of the tensile strained AlN layer provides a predetermined dislocation density. 
     
     
         4 . The light emitting device of  claim 3 , wherein the thickness is between 1×10 8  cm −2  and 2×10 10  cm −2 . 
     
     
         5 . The light emitting device of  claim 1 , wherein the thickness of the compressive strained GaN layer provides a predetermined dislocation density. 
     
     
         6 . The light emitting device of  claim 5 , wherein the thickness is between 1×10 8  cm −2  and 2×10 10  cm −2 . 
     
     
         7 . The light emitting device of  claim 1 , wherein the thickness of the compressive strained AlGaN layer provides a predetermined dislocation density. 
     
     
         8 . The light emitting device of  claim 7 , wherein the thickness is between 1×10 8  cm −2  and 2×10 10  cm −2 . 
     
     
         9 . The light emitting device of  claim 1 , wherein the compressive strained AlGaN layer is an Al x Ga 1-x N layer, wherein ‘x’ is a number between 0 and 1. 
     
     
         10 . The light emitting device of  claim 9  further comprising:
 a strained Al y Ga 1-x N layer between the Al x Ga 1-x N layer and the compressive strained GaN layer and the  . 
 
     
     
         11 . The light emitting device of  claim 1 , wherein the thickness of the compressive strained buffer layer is greater than zero and less than or equal at least one of:
 5 μm;   4 μm; and   3 μm.   
     
     
         12 . The light emitting device of  claim 1 , wherein the thickness of the tensile strained AlN layer is greater than zero and less than or equal to at least one of:
 1 μm;   0.5 μm; and   0.4 μm.   
     
     
         13 . The light emitting device of  claim 1 , wherein the thickness of the compressive strained AlGaN layer is greater than zero and less than or equal to at least one of:
 1 μm;   0.8 μm; and   0.7 μm.   
     
     
         14 . The light emitting device of  claim 1 , wherein the thickness of the compressive strained GaN layer is greater than zero and less than or equal to at least one of:
 4 μm;   3 μm; and   2.5 μm.   
     
     
         15 . The light emitting device of  claim 1  further comprising:
 an electron blocking layer between the active layer and the p-type layer, wherein the electron blocking layer reduces the recombination of electrons with holes in the p-type layer. 
 
     
     
         16 . The light emitting device of  claim 1  further comprising:
 an optical reflector adjacent the p-type layer. 
 
     
     
         17 . The light emitting device of  claim 1 , wherein the compressive strained AlGaN layer is compositionally graded in Al and Ga such that:
 a first surface of the compressive strained AlGaN layer has an Al content that is greater than the Ga content, the first surface being a surface adjacent the tensile strained AlN layer; and   a second surface of the compressive strained AlGaN layer has a Ga content that is greater than an Al content, the second surface being a surface adjacent the compressive strained GaN layer.   
     
     
         18 . The light emitting device of  claim 1 , wherein the compressive strained AlGaN layer is compositionally graded in Al content and Ga content such that:
 a first surface of the compressive strained AlGaN layer has a Ga content that is greater than an Al content, the first surface being a surface adjacent the compressive strained GaN layer; and   a second surface of the compressive strained AlGaN layer has an Al content that is greater than the Ga content, the second surface being a surface adjacent the tensile strained AlN layer.   
     
     
         19 . A light emitting device comprising:
 a silicon substrate;   a compressive strained buffer layer comprising:
 a tensile strained AlN layer adjacent the substrate, 
 a compressive strained GaN layer adjacent the n-type layer; and 
 a compressive strained AlGaN layer between the compressive strained GaN layer and the tensile strained AlN layer, wherein the compressive strained GaN layer is thicker than the compressive strained AlGaN layer, and the compressive strained AlGaN layer is thicker than the tensile strained AlN layer; and 
   a device stack between the substrate and the compressive strained buffer layer, the device stack comprising:
 an n-type layer, 
 a p-type layer, 
 an active layer between the n-type layer and the p-type layer.