Increasing the brightness of III-Nitride light emitting devices

Abstract

LEDs employing a III-Nitride light emitting active region deposited on a base layer above a substrate show improved optical properties with the base layer grown on an intentionally misaligned substrate with a thickness greater than 3.5 μm. Improved brightness, improved quantum efficiency, and a reduction in the current at which maximum quantum efficiency occurs are among the improved optical properties resulting from use of a misaligned substrate and a thick base layer. Illustrative examples are given of misalignment angles in the range from 0.05° to 0.50°, and base layers in the range from 6.5 to 9.5 μm although larger values of both misalignment angle and base layer thickness can be used. In some cases, the use of thicker base layers provides sufficient structural support to allow the substrate to be removed from the device entirely.

What is being claimed is:  
     
         1 . A method comprising: 
 providing a sapphire substrate having an upper face wherein said upper face is misaligned from a main crystal plane of said substrate at least 0.05°;    depositing a base layer above said upper face of said substrate wherein said base layer has a thickness exceeding about 3.5 micrometers;    doping at least a portion of said base layer with an n-type dopant; and    forming a III-Nitride light emitting region above said base layer.    
     
     
         2 . The method of  claim 1  further comprising removing said substrate following said depositing said base layer thereon.  
     
     
         3 . The method of  claim 1  wherein said upper face of said sapphire substrate is misaligned from a main crystal plane of said substrate at an angle between about 0.05° and about 10°.  
     
     
         4 . The method of  claim 1  wherein said upper face of said sapphire substrate is misaligned from a main crystal plane of said substrate at an angle between about 0.05° and about 5°.  
     
     
         5 . The method of  claim 1  wherein said upper face of said sapphire substrate is misaligned from a main crystal plane of said substrate at an angle between about 0.05° and about 1°.  
     
     
         6 . The method of  claim 1  wherein said thickness is between about 3.5 micrometers to about 200 micrometers.  
     
     
         7 . The method of  claim 1  wherein said thickness is between about 3.5 micrometers to about 20 micrometers.  
     
     
         8 . The method of  claim 1  wherein said thickness is between about 3.5 micrometers to about 10 micrometers.  
     
     
         9 . The method of  claim 1  wherein said thickness is between about 3.5 micrometers to about 7 micrometers.  
     
     
         10 . The method of  claim 1  wherein said main crystal plane is the c-plane.  
     
     
         11 . The method of  claim 1  wherein said main crystal plane is the r-plane.  
     
     
         12 . The method of  claim 1  wherein said main crystal plane is the a-plane.  
     
     
         13 . The method of  claim 1  wherein said main crystal plane is the m-plane.  
     
     
         14 . The method of  claim 1  wherein doping at least a portion of said base layer comprises increasing a doping level of the base layer in a direction towards said light-emitting region.  
     
     
         15 . The method of  claim 1  wherein: 
 depositing a base layer comprises depositing a first sublayer above said upper face and a second sublayer above said first sublayer; and  
 doping at least a portion of the base layer comprises doping said second sublayer more heavily than said first sublayer.  
 
     
     
         16 . The method of  claim 15  wherein said first sublayer has a dopant concentration less than about 5×10 18  cm −3  and said second sublayer has a dopant concentration of at least about 10 18  cm −3 .  
     
     
         17 . The method of  claim 15  wherein depositing a base layer further comprises depositing a third sublayer over the second sublayer.  
     
     
         18 . A method comprising: 
 providing a substrate having an upper face wherein said upper face is misaligned from a main crystal plane of said substrate at least 0.05°;    depositing a base layer above said upper face of said substrate wherein said base layer has a thickness exceeding about 5.5 micrometers; and    forming a III-Nitride light emitting region above said base layer.    
     
     
         19 . The method of  claim 18  further comprising removing said substrate following said depositing said base layer thereon.  
     
     
         20 . The method of  claim 18  wherein said thickness is between about 6.5 micrometers to about 200 micrometers.  
     
     
         21 . The method of  claim 18  wherein said thickness is between about 6.5 micrometers to about 20 micrometers.  
     
     
         22 . The method of  claim 18  wherein said thickness is between about 6.5 micrometers to about 10 micrometers.  
     
     
         23 . The method of  claim 18  wherein providing a substrate comprises providing a substrate selected from the group consisting of sapphire, silicon carbide, gallium nitride, gallium arsenide, and gallium phosphide.  
     
     
         24 . The method of  claim 18  further comprising doping at least a portion of the base layer.  
     
     
         25 . The method of  claim 24  wherein doping at least a portion of said base layer comprises increasing a doping level of the base layer in a direction towards the light-emitting region.  
     
     
         26 . The method of  claim 24  wherein: 
 depositing a base layer comprises depositing a first sublayer above said upper face and a second sublayer above said first sublayer; and  
 doping at least a portion of the base layer comprises doping said second sublayer more heavily than said first sublayer.  
 
     
     
         27 . The method of  claim 26  wherein said first sublayer has a dopant concentration less than about 5×10 18  cm −3  and said second sublayer has a dopant concentration of at least about 10 18  cm −3 .  
     
     
         28 . The method of  claim 26  wherein depositing a base layer further comprises depositing a third sublayer over the second sublayer.  
     
     
         29 . The method of  claim 18  wherein said upper face of said substrate is misaligned from a main crystal plane of said substrate at an angle between about 0.05° and about 10°.  
     
     
         30 . The method of  claim 18  wherein said upper face of said substrate is misaligned from a main crystal plane of said substrate at an angle between about 0.05° and about 5°.  
     
     
         31 . The method of  claim 18  wherein said upper face of said substrate is misaligned from a main crystal plane of said substrate at an angle between about 0.05° and about 1°.