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 buffer layer comprising an aluminum gallium nitride layer and a gallium nitride (GaN) layer adjacent to the aluminum gallium nitride layer; and   a light emitting stack adjacent to the buffer layer, the light emitting stack including an active layer configured to generate light upon the recombination of electrons and holes, wherein a combined thickness of the buffer layer and the light emitting stack is less than or equal to 5 micrometers (μm).   
     
     
         2 . The light emitting device of  claim 1 , wherein said buffer layer is adjacent to a silicon substrate. 
     
     
         3 . The light emitting device of  claim 1 , wherein the buffer layer further comprises an aluminum nitride (AlN) layer. 
     
     
         4 . The light emitting device of  claim 3 , wherein the AlN layer is adjacent to the silicon substrate and the GaN layer is adjacent to the light emitting stack. 
     
     
         5 . The light emitting device of  claim 1 , wherein the combined thickness is less than or equal to 3 μm. 
     
     
         6 . The light emitting device of  claim 1 , wherein the light emitting device has a radius of curvature (absolute value) that is greater than 50 m. 
     
     
         7 . A light emitting device, comprising:
 a buffer layer including an aluminum gallium nitride layer and a gallium nitride (GaN) layer adjacent to the aluminum gallium nitride layer; and   a light emitting stack adjacent to the GaN layer, the light emitting stack having an active layer configured to generate light upon the recombination of electrons and holes,   wherein an absolute value of a radius of curvature of the buffer layer is greater than 50 m.   
     
     
         8 . The light emitting device of  claim 7 , wherein the buffer layer further comprises an aluminum nitride (AlN) layer. 
     
     
         9 . The light emitting device of  claim 7 , wherein said buffer layer is adjacent to a silicon substrate. 
     
     
         10 . The light emitting device of  claim 7 , wherein a combined thickness of the buffer layer and the light emitting stack is less than or equal to about 5 micrometers (μm). 
     
     
         11 . The light emitting device of  claim 7 , wherein the buffer layer has a defect density between about 1×10 8  cm −2  and 2×10 10  cm −2 . 
     
     
         12 . A light emitting device, comprising:
 a buffer layer comprising:
 i) a compressive strained Al x Ga 1-x N layer adjacent to the AlN layer, wherein ‘x’ is a number between 0 and 1; and 
 ii) a compressive strained gallium nitride (GaN) layer adjacent to the strained Al x Ga 1-x N layer; and 
   a light emitting stack adjacent to the buffer layer, the light emitting stack having an n-type gallium nitride (n-GaN) layer, a p-type gallium nitride (p-GaN) layer, and an active layer between the n-GaN and p-GaN layers, the active layer configured to generate light upon the recombination of electrons and holes.   
     
     
         13 . The light emitting device of  claim 12 , wherein the buffer layer further comprises a tensile strained aluminum nitride (AlN) layer. 
     
     
         14 . The light emitting device of  claim 13 , further comprising an electrode adjacent to the tensile strained AlN layer. 
     
     
         15 . The light emitting device of  claim 12 , further comprising a substrate adjacent to the buffer layer or the light emitting stack. 
     
     
         16 . The light emitting device of  claim 15 , wherein the substrate is formed of a material selected from the group consisting of silicon, germanium, silicon oxide, silicon dioxide, titanium oxide, titanium dioxide, sapphire, silicon carbide (SiC), a ceramic material and a metallic material. 
     
     
         17 . The light emitting device of  claim 12 , wherein a combined thickness of the buffer layer and the light emitting stack is less than or equal to about 5 micrometers (μm). 
     
     
         18 . The light emitting device of  claim 12 , wherein a thickness of the strained AN layer is less than or equal to about 1 micrometer (μm). 
     
     
         19 . The light emitting device of  claim 12 , wherein a thickness of the strained Al x Ga 1-x N layer is less than or equal to about 1 micrometer (μm). 
     
     
         20 . The light emitting device of  claim 12 , wherein a thickness of the strained GaN layer is less than or equal to about 4 micrometers (μm). 
     
     
         21 . The light emitting device of  claim 12 , wherein the n-GaN layer is adjacent to the strained GaN layer. 
     
     
         22 . The light emitting device of  claim 12 , wherein a thickness of the buffer layer is less than or equal to about 5 micrometers (μm). 
     
     
         23 . The light emitting device of  claim 12 , wherein the strained GaN layer has a defect density between about 1×10 8  cm −2  and 2×10 10  cm −2 . 
     
     
         24 . The light emitting device of  claim 12 , wherein the light emitting stack has a defect density between about 1×10 8  cm −2  and 2×10 10  cm −2 . 
     
     
         25 . The light emitting device of  claim 24 , wherein the defects are V-defects originating from dislocations in the buffer layer. 
     
     
         26 . The light emitting device of  claim 12 , further comprising an electrode adjacent to the light emitting stack. 
     
     
         27 . The light emitting device of  claim 12 , further comprising a strained Al y Ga 1-y N layer adjacent to the strained Al x Ga 1-x N layer, wherein ‘y’ is a number between 0 and 1. 
     
     
         28 . A light emitting device, comprising a buffer layer adjacent to a light emitting stack, the light emitting stack having an active layer configured to generate light upon the recombination of electrons and holes, said active layer having an n-type gallium nitride layer and a p-type gallium nitride layer,
 wherein the buffer layer has a radius of curvature (absolute value) that is greater than 50 m.   
     
     
         29 . The light emitting device of  claim 28 , wherein the buffer layer comprises aluminum, gallium and nitrogen, wherein the buffer layer is compositionally graded between aluminum nitride and gallium nitride. 
     
     
         30 . A method for forming a light emitting device, comprising:
 forming, over a substrate in a reaction chamber, a light emitting stack having an active layer configured to generate light upon the recombination of electrons and holes,   wherein the light emitting stack is formed adjacent to a gallium nitride (GaN) layer,   wherein the GaN layer is formed adjacent to an aluminum gallium nitride layer under processing conditions selected to form defects in the GaN layer,   wherein the aluminum gallium nitride layer is formed adjacent to an aluminum nitride (AlN) layer under processing conditions selected to form defects in the aluminum gallium nitride layer, and   wherein the AlN layer is formed adjacent to said substrate under processing conditions selected to form defects in the AlN layer.   
     
     
         31 . The method of  claim 30 , wherein the substrate is formed of a material selected from the group consisting of silicon, germanium, silicon oxide, silicon dioxide, titanium oxide, titanium dioxide, sapphire, silicon carbide (SiC), a ceramic material and a metallic material. 
     
     
         32 . The method of  claim 30 , wherein the light emitting stack is formed under processing conditions selected to generate V-defects originating from dislocations in the GaN layer. 
     
     
         33 . The method of  claim 30 , wherein the GaN layer is formed under processing conditions selected to generate compressive strain in the GaN layer. 
     
     
         34 . The method of  claim 30 , wherein the aluminum gallium nitride layer is formed under processing conditions selected to generate compressive strain in the aluminum gallium nitride layer. 
     
     
         35 . The method of  claim 30 , wherein the AlN layer is formed under processing conditions selected to generate tensile strain in the AlN layer. 
     
     
         36 . The method of  claim 30 , wherein the processing conditions are selected from the group consisting of reaction space chamber, precursor flow rate, carrier gas flow rate and growth temperature. 
     
     
         37 . The method of  claim 30 , wherein said defects are dislocations. 
     
     
         38 . A method for forming a light emitting device, comprising:
 (a) providing a substrate in a reaction chamber;   (b) forming an aluminum nitride (AlN) layer adjacent to the substrate under processing conditions selected to generate defects in the AlN layer;   (c) forming an aluminum gallium nitride layer adjacent to the AlN layer under processing conditions selected to generate defects in the aluminum gallium nitride layer; and   (d) forming a gallium nitride (GaN) layer adjacent to the aluminum gallium nitride layer under processing conditions selected to generate defects in the GaN layer.   
     
     
         39 . The method of  claim 38 , further comprising (e) forming a light emitting stack adjacent to the GaN layer under processing conditions selected to generate V-defects originating from dislocations in the GaN layer. 
     
     
         40 . The method of  claim 38 , wherein the aluminum gallium nitride layer is Al x Ga 1-x N, wherein ‘x’ is a number between 0 and 1. 
     
     
         41 . The method of  claim 38 , further comprising forming an additional aluminum gallium nitride layer between the aluminum gallium nitride layer and the GaN layer. 
     
     
         42 . The method of  claim 38 , further comprising forming a light emitting stack adjacent to the GaN layer, the light emitting stack comprising an active layer configured to generate light upon the recombination of electrons and holes. 
     
     
         43 . The method of  claim 38 , wherein the light emitting stack comprises an n-type gallium nitride (n-GaN) layer, a p-type gallium nitride (p-GaN) layer, and said active layer between the n-GaN and the p-GaN layers. 
     
     
         44 . The method of  claim 43 , wherein the n-GaN layer is adjacent to the GaN layer. 
     
     
         45 . A method for forming a light emitting device, comprising:
 forming a plurality of layers adjacent to a substrate, said plurality of layers including i) an aluminum nitride layer adjacent to the substrate, ii) an aluminum gallium nitride layer adjacent to the aluminum nitride layer and iii) a gallium nitride layer adjacent to the aluminum gallium nitride layer,   wherein, during the formation of each of said plurality of layers, one or more process parameters are selected such that an individual layer of said plurality of layers has a strain that is nonzero with increasing thickness of said individual layer.   
     
     
         46 . The method of  claim 45 , wherein the substrate is formed of a material selected from the group consisting of silicon, germanium, silicon oxide, silicon dioxide, titanium oxide, titanium dioxide, sapphire, silicon carbide (SiC), a ceramic material and a metallic material. 
     
     
         47 . The method of  claim 45 , wherein during the formation of the aluminum nitride layer, one or more process parameters are selected such that the aluminum nitride layer has a tensile strain that is nonzero with increasing thickness of the aluminum nitride layer. 
     
     
         48 . The method of  claim 45 , wherein during the formation of the aluminum gallium nitride layer, one or more process parameters are selected such that the aluminum gallium nitride layer has a compressive strain that is nonzero with increasing thickness of the aluminum gallium nitride layer. 
     
     
         49 . The method of  claim 45 , wherein during the formation of the gallium nitride layer, one or more process parameters are selected such that the gallium nitride layer has a compressive strain that is nonzero with increasing thickness of the gallium nitride layer 
     
     
         50 . The method of  claim 45 , wherein said individual layer of said plurality of layers has a strain that is nonzero with increasing thickness of said individual layer at a growth temperature of said individual layer. 
     
     
         51 . A system for forming a light emitting device, comprising:
 a reaction chamber for holding a substrate;   a pumping system in fluid communication with the reaction chamber, the pumping system configured to purge or evacuate the reaction chamber; and   a computer system having a processor for executing machine readable code implementing a method for forming a buffer layer adjacent to the substrate, the method comprising:
 forming a plurality of layers adjacent to said substrate, said plurality of layers including i) an aluminum nitride layer adjacent to the substrate, ii) an aluminum gallium nitride layer adjacent to the aluminum nitride layer and iii) a gallium nitride layer adjacent to the aluminum gallium nitride layer, 
 wherein, during the formation of each of said plurality of layers, one or more process parameters are selected such that an individual layer of said plurality of layers has a strain that is nonzero with increasing thickness of said individual layer.