Strain-controlled III-nitride light emitting device

Abstract

In a III-nitride light emitting device, a ternary or quaternary light emitting layer is configured to control the degree of phase separation. In some embodiments, the difference between the InN composition at any point in the light emitting layer and the average InN composition in the light emitting layer is less than 20%. In some embodiments, control of phase separation is accomplished by controlling the ratio of the lattice constant in a relaxed, free standing layer having the same composition as the light emitting layer to the lattice constant in a base region. For example, the ratio may be between about 1 and about 1.01.

1 . A III-nitride light emitting device comprising: 
 a nucleation region;    a base region formed on the nucleation region, the base region having a lattice constant a 1 ; and    a light emitting layer overlying the base region and disposed between an n-type region and a p-type region; wherein: 
 the light emitting layer has an average InN composition greater than 8%;  
 a relaxed, free standing layer having a same composition as the light emitting layer has a lattice constant a 2 ; and  
 a ratio of a 2  to a 1 , is between about 1 and about 1.01.  
   
     
     
         2 . The device of  claim 1  wherein the light emitting layer is configured to emit light having a peak emission wavelength greater than 420 nm.  
     
     
         3 . The device of  claim 1  wherein the base region is Al x In y Ga z N, where 0≦x≦1, 0≦y≦1, and 0≦z≦1.  
     
     
         4 . The device of  claim 1  wherein the base region is In x Ga y N, where 0≦x≦1 and 0≦y≦1.  
     
     
         5 . The device of  claim 1  wherein a dislocation density in the base region, n-type region, light emitting layer, and p-type region is less than about 5×10 8  cm −2 .  
     
     
         6 . The device of  claim 1  wherein: 
 the light emitting layer is In x Ga y N where 0.08≦x≦1; and    the base region is In a Ga b N where (x−0.08)≦a≦1.    
     
     
         7 . The device of  claim 1  further comprising: 
 a first contact electrically connected to the n-type region;    a second contact electrically connected to the p-type region;    a lead frame electrically connected to the first and second contacts; and    a cover overlying the light emitting layer.    
     
     
         8 . The device of  claim 1  wherein the light emitting layer has a thickness greater than 5 nm.  
     
     
         9 . The device of  claim 1  wherein the light emitting layer has a thickness greater than 10 nm.  
     
     
         10 . The device of  claim 1  wherein the light emitting layer is a first quantum well, the device further comprising: 
 a second quantum well; and    a barrier layer disposed between the first and second quantum well.    
     
     
         11 . The device of  claim 1  wherein the light emitting layer and any layers between the light emitting layer and the base region are strained.  
     
     
         12 . The device of  claim 1  wherein the base region is the n-type region.  
     
     
         13 . A III-nitride light emitting device comprising: 
 a substrate;    a base region formed on the substrate, the base region having a lattice constant a 1 ; and    a light emitting layer overlying the base region and disposed between an n-type region and a p-type region; wherein: 
 the light emitting layer has an average InN composition greater than 8%;  
 a relaxed, free standing layer having a same composition as the light emitting layer has a lattice constant a 2 ; and  
 a ratio of a 2  to a 1 , is between about 1 and about 1.01.  
   
     
     
         14 . The device of  claim 13  wherein the light emitting layer is configured to emit light having a peak emission wavelength greater than 420 nm.  
     
     
         15 . The device of  claim 13  wherein the base region is Al x In y Ga z N, where 0≦x≦1, 0≦y≦1, and 0≦z≦1.  
     
     
         16 . The device of  claim 13  wherein the base region is In x Ga y N, where 0≦x≦1 and 0≦y≦1.  
     
     
         17 . The device of  claim 13  wherein: 
 the light emitting layer is In x Ga y N where 0.08≦x≦1; and    the base region is In a Ga b N where (x−0.08)≦a≦1.    
     
     
         18 . The device of  claim 13  wherein the substrate is SiC.  
     
     
         19 . A method comprising: 
 growing an epitaxial stack on a growth substrate, the epitaxial stack comprising: 
 a base region having a lattice constant a 1 ; and  
 a light emitting layer overlying the base region and disposed between an n-type region and a p-type region;  
   bonding the epitaxial stack to a host substrate; and    removing the growth substrate; wherein: 
 the light emitting layer has an average InN composition greater than 8%;  
 a relaxed, free standing layer having a same composition as the light emitting layer has a lattice constant a 2 ; and  
 a ratio of a 2  to a 1 , is between about 1 and about 1.01.  
   
     
     
         20 . The method of  claim 19  wherein the light emitting layer is configured to emit light having a peak emission wavelength greater than 420 nm.  
     
     
         21 . The method of  claim 19  wherein the base region is Al x In y Ga z N, where 0≦x≦1, 0≦y≦1, and 0≦z≦1.  
     
     
         22 . The method of  claim 19  wherein the base region is In x Ga y N where 0≦x≦1 and 0≦y≦1.  
     
     
         23 . The method of  claim 19  wherein: 
 the light emitting layer is In x Ga y N where 0.08≦x≦1; and    the base region is In a Ga b N where (x−0.08)≦a≦1.