Group III nitride LED with undoped cladding layer and multiple quantum well

Abstract

The present invention is a semiconductor structure for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum. The structure includes a first n-type cladding layer of Al x In y Ga 1−x−y N, where 0≦x≦1 and 0≦y<1 and (x+y)≦1; a second n-type cladding layer of Al x In y Ga 1−x−y N, where 0≦x≦1 and 0≦y<1 and (x+y)≦1, wherein the second n-type cladding layer is further characterized by the substantial absence of magnesium; an active portion between the first and second cladding layers in the form of a multiple quantum well having a plurality of In x Ga 1−x N well layers where 0<x<1 separated by a corresponding plurality of Al x In y Ga 1−x−y N barrier layers where 0≦x≦1 and 0≦y≦1; a p-type layer of a Group III nitride, wherein the second n-type cladding layer is positioned between the p-type layer and the multiple quantum well; and wherein the first and second n-type cladding layers have respective bandgaps that are each larger than the bandgap of the well layers. In preferred embodiments, a Group III nitride superlattice supports the multiple quantum well.

That which is claimed is: 
     
       1. A semiconductor structure for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum, said structure comprising:
 a first n-type cladding layer of Al x In y Ga 1−x−y N, where 0≦x≦1 and 0≦y<1 and (x+y)≦1; 
 a second n-type cladding layer of Al x In y Ga 1−x−y N where 0≦x≦1 and 0≦y<1 and (x+y)≦1, wherein said second n-type cladding layer is further characterized by the substantial absence of magnesium, and wherein a composition of said second n-type cladding layer is graded; 
 an active portion between said first and second cladding layers in the form of a multiple quantum well having a plurality of In x Ga 1−x N well layers where 0<x<1 separated by a corresponding plurality of Al x In y Ga 1−x−y N barrier layers where 0≦x≦1 and 0≦y≦1; 
 a p-type layer of a Group III nitride, wherein said second n-type cladding layer is positioned between said p-type layer and said multiple quantum well; 
 wherein said first and second n-type cladding layers have respective bandgaps that are each larger than the bandgap of said well layers, wherein a p-n junction is defined between said second n-type cladding layer and said p-type layer. 
 
     
     
       2. A structure according to  claim 1  wherein said barrier layers comprise Al x In y Ga 1−x−y N where 0≦x<1 and 0<y<1. 
     
     
       3. A structure according to  claim 1  wherein said barrier layers comprise Al x In y Ga 1−x−y N where 0<x<1 and 0≦y<1 and x+y≦1. 
     
     
       4. A structure according to  claim 1  wherein said barrier layers in said multiple quantum well have larger bandgaps than said well layers in said multiple quantum well. 
     
     
       5. A structure according to  claim 1  wherein at least one of said barrier layers in said multiple quantum well is undoped. 
     
     
       6. A structure according to  claim 1  wherein at least one of said well layers in said multiple quantum well is undoped. 
     
     
       7. A semiconductor structure according to  claim 1 , wherein said multiple quantum well has a first surface and a second surface, said first surface of said multiple quantum well being in contact with said first n-type cladding layer and said second surface of said multiple quantum well being in contact with said second n-type cladding layer. 
     
     
       8. A semiconductor structure according to  claim 1 , wherein said second n-type cladding layer has a first surface and a second surface, said first surface of said second n-type cladding layer being in contact with said multiple quantum well, and said second surface of said second n-type cladding layer being in contact with said p-type layer, wherein the composition of said second n-type cladding layer is progressively graded such that the crystal lattice at said first surface of said second n-type cladding layer more closely matches the crystal lattice of said multiple quantum well, and the crystal lattice at said second surface of said second n-type cladding layer more closely matches the crystal lattice of said p-type layer. 
     
     
       9. A semiconductor structure according to  claim 1 , wherein said p-type layer is in contact with said second n-type cladding layer, opposite said multiple quantum well. 
     
     
       10. A semiconductor structure according to  claim 1 , wherein said second n-type cladding layer consists essentially of Al x Ga 1−x N, where 0<x <1. 
     
     
       11. A semiconductor structure according to  claim 1 , wherein said active layer portion consists essentially of In y Ga 1−y N, where 0<y<1. 
     
     
       12. A semiconductor structure according to  claim 1 , wherein said p-type layer is magnesium-doped gallium nitride. 
     
     
       13. A semiconductor structure according to  claim 12 , wherein said second n-type cladding layer is thick enough to deter migration of magnesium from said p-type layer to said multiple quantum well, yet thin enough to facilitate recombination in said multiple quantum well. 
     
     
       14. A semiconductor structure according to  claim 1 , wherein said p-type layer is indium nitride. 
     
     
       15. A semiconductor structure according to  claim 1 , wherein said p-type layer is In x Ga 1−x N, where 0<x<1. 
     
     
       16. A semiconductor structure according to  claim 1 , wherein said p-type layer comprises a superlattice formed from a plurality of Group III nitride layers selected from the group consisting of gallium nitride, indium nitride, and In x Ga 1−x N, where 0<x<1. 
     
     
       17. A semiconductor structure according to  claim 16 , wherein said superlattice is formed from alternating layers of two Group III nitride layers selected from the group consisting of gallium nitride, indium nitride, and In x Ga 1−x N, where 0<x<1. 
     
     
       18. A semiconductor structure according to  claim 1 , further comprising a third n-type layer of Al x In y Ga 1−x−y N, where 0≦x≦1 and 0≦y<1 and (x+y)≦1, wherein said third n-type layer is positioned between said second n-type cladding layer and said p-type layer multiple quantum well. 
     
     
       19. A semiconductor structure according to  claim 18 , wherein said third n-type layer has a first surface and a second surface, said first surface of said third n-type layer being in contact with said p-type layer multiple quantum well and said second surface of said third n-type layer being in contact with said second n-type cladding layer. 
     
     
       20. A semiconductor structure according to  claim 1 , further comprising an n-type silicon carbide substrate, wherein said first n-type cladding layer is positioned between said silicon carbide substrate and said multiple quantum well. 
     
     
       21. A semiconductor structure according to  claim 15 , further comprising:
 a silicon carbide substrate, wherein said first n-type cladding layer is positioned between said silicon carbide substrate and said multiple quantum well; and  
 discrete crystal portions selected from the group consisting of gallium nitride and indium gallium nitride, said discrete crystal portions positioned between said first n-type cladding layer and said silicon carbide substrate, said discrete crystal portions being present in an amount sufficient to reduce the a barrier between said first n-type cladding layer and said silicon carbide substrate, but less than an amount that would detrimentally affect the function functionality of any resulting a light emitting device formed on said silicon carbide substrate. 
 
     
     
       22. A semiconductor structure according to  claim 1 , further comprising:
 an n-type-silicon carbide substrate; and 
 a conductive buffer layer positioned between said silicon carbide substrate and said first n-type cladding layer. 
 
     
     
       23. A semiconductor structure according to  claim 22 , wherein said conductive buffer layer has a first surface and a second surface, said first surface of said conductive buffer layer being in contact with said silicon carbide substrate and said second surface of said conductive buffer layer being in contact with said first n-type cladding layer. 
     
     
       24. A semiconductor structure according to  claim 22 , wherein said conductive buffer layer consists essentially of aluminum gallium nitride having the formula Al x Ga 1−1 N, where 0<x<1. 
     
     
       25. A semiconductor structure according to  claim 22 , further comprising an n-type transition layer of a Group III nitride, said transition layer being positioned between said conductive buffer layer and said first n-type cladding layer. 
     
     
       26. A semiconductor structure according to  claim 22 , further comprising discrete crystal portions selected from the group consisting of gallium nitride and indium gallium nitride, said discrete crystal portions positioned between said conductive buffer layer and said silicon carbide substrate, said discrete crystal portions being present in an amount sufficient to reduce the a barrier between said conductive buffer layer and said silicon carbide substrate, but less than an amount that would detrimentally affect the function functionality of any resulting a light emitting device formed on said silicon carbide substrate. 
     
     
       27. A semiconductor structure for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum, said structure comprising:
 an active portion in the form of a multiple quantum well having a plurality of In x Ga 1−x N well layers where 0<x<1 separated by a corresponding plurality of Al x In y Ga 1−x−y N barrier layers where 0≦x≦1 and 0≦y≦1; 
 a Group III nitride superlattice supporting said multiple quantum well; 
 a layer of Al x In y Ga 1−x−y N, where 0<x≦1 and 0≦y≦1 and (x+y)≦1 adjacent said multiple quantum well and opposite from said superlattice with respect to said multiple quantum well and being characterized by the substantial absence of magnesium, wherein a composition of said layer of Al x In y Ga 1−x−y N is graded; 
 a first p-type layer of a Group III nitride adjacent said AlInGaN layer of Al x In y Ga 1−x−y N and opposite said multiple quantum well with respect to said AlInGaN layer of Al x In y Ga 1−x−y N, wherein a p-n junction is defined between said layer of Al x In y Ga 1−x−y N and said first p-type layer; and 
 an n-type Group III nitride layer supporting said superlattice and opposite from said multiple quantum well with respect to said superlattice. 
 
     
     
       28. A semiconductor structure according to  claim 27  and further comprising a silicon carbide substrate and a conductive Group III nitride buffer layer on said substrate, with said substrate and said conductive buffer layer supporting the a remainder of said structure. 
     
     
       29. A semiconductor structure according to  claim 28  and further comprising:
 an additional n-type GaN layer between said conductive buffer layer and said supporting n-type layer; 
 a p-type contact layer on said first p-type layer; 
 an ohmic contact to said p-type contact layer; and 
 an ohmic contact to said substrate. 
 
     
     
       30. A semiconductor structure according to  claim 27  wherein said superlattice comprises alternating layers of In x Ga 1−x N and In y Ga 1−y N where 0≦x≦1 and 0≦y≦1 and x does not equal y. 
     
     
       31. A semiconductor structure according to  claim 30  wherein x equals 0 and 0<y<1. 
     
     
       32. A semiconductor structure according to  claim 30  wherein said superlattice contains between 5 and 50 periods. 
     
     
       33. A semiconductor structure according to  claim 30  wherein said superlattice contains 25 periods. 
     
     
       34. A semiconductor structure according to  claim 30  wherein said superlattice contains 10 periods. 
     
     
       35. A semiconductor structure for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum, said structure comprising:
 a silicon carbide substrate; 
 a conductive Group III nitride buffer layer on said substrate; 
 a first n-type GaN layer on said conductive buffer layer; 
 a second n-type Group III nitride layer on said first n-type GaN layer; 
 a superlattice on said second GaN n-type Group III nitride layer and formed of alternating layers of GaN and In y Ga 1−y N where 0<y<1; 
 an active portion on said superlattice in the form of a multiple quantum well having a plurality of In x Ga 1−x N well layers where 0<x<1 separated by a corresponding plurality of Al x In y Ga 1−x−y N barrier layers where 0≦x≦1 and 0≦y≦1; 
 a layer of Al x In y Ga 1−x−y N, where 0≦x≦1 and 0≦y≦1 and (x+y)≦1 on said multiple quantum well and being characterized by the substantial absence of magnesium, wherein a composition of said layer of Al x In y Ga 1−x−y N is graded; 
 a first p-type layer of a Group III nitride on said AlInGaN layer of Al x In y Ga 1−x−y N, wherein a p-n junction is defined between said layer of Al x In y Ga 1−x−y N and said first p-type layer; 
 a p-type contact layer on said first p-type layer; 
 an ohmic contact to said p-type contact layer; and 
 an ohmic contact to said substrate. 
 
     
     
       36. A structure according to  claim 35  wherein said barrier layers in said multiple quantum well have large bandgaps than said well layers in said multiple quantum well. 
     
     
       37. A structure according to  claim 35  wherein at least one of said barrier layer layers in said multiple quantum well is undoped. 
     
     
       38. A structure according to  claim 35  wherein at least one of said well layers in said multiple quantum well is undoped. 
     
     
       39. A semiconductor structure according to  claim 35 , further comprising discrete crystal portions selected from the group consisting of gallium nitride and indium gallium nitride, said discrete crystal portions positioned between said first n-type cladding conductive Group III nitride buffer layer and said silicon carbide substrate, said discrete crystal portions being present in an amount sufficient to reduce the a barrier between said first n-type cladding conductive Group III nitride buffer layer and said silicon carbide substrate, but less than an amount that would detrimentally affect the function functionality of any resulting a light emitting device formed on said silicon carbide substrate. 
     
     
       40. A structure according to claim 1 wherein the composition of said second n-type cladding layer is graded in a stepwise fashion.  
     
     
       41. A structure according to claim 1 wherein the composition of said second n-type cladding layer is graded in a continuous fashion.  
     
     
       42. A structure according to claim 1, wherein the p-n junction comprises a p-n homojunction between said second n-type cladding layer and said p-type layer.  
     
     
       43. A structure according to claim 1, wherein, at the p-n junction, said second n-type cladding layer and said p-type layer comprise aluminum.  
     
     
       44. A semiconductor structure according to claim 27, wherein, at the p-n junction, said layer of Al x In y Ga 1−x−y N and said first p-type layer comprise aluminum.  
     
     
       45. A semiconductor structure according to claim 35, wherein, at the p-n junction, said layer of Al x In y Ga 1−x−y N and said first p-type layer comprise aluminum.