Semiconductor light emitting devices with graded composition light emitting layers

1. A semiconductor light emitting device comprising a III-nitride light emitting layer disposed between an n-type region and a p-type region, the light emitting layer having a graded composition of a first element, wherein a change in composition of the first element in the light emitting layer is greater than 0.2% per angstrom and less than 0.8% per angstrom across a thickness of the light emitting layer.

2. The device of claim 1 wherein a change in composition of the first element in the light emitting layer is at least 0.4% per angstrom across a thickness of the light emitting layer.

3. The device of claim 1 wherein the light emitting layer is In x Ga 1−x N and the first element is indium.

4. The device of claim 1 wherein a change in composition of the first element in the light emitting layer is at least 0.6% per angstrom across a thickness of the light emitting layer.

5. The device of claim 1 wherein the light emitting layer has a thickness between 10 angstroms and 100 angstroms.

6. A semiconductor light emitting device comprising a III-nitride light emitting layer disposed between an n-type region and a p-type region, the light emitting layer having a graded composition of a first element, wherein a change in composition of the first element in the light emitting layer is greater than 0.2% per angstrom and less than 1% per angstrom across a thickness of the light emitting layer, wherein the light emitting layer has a thickness between 100 angstroms and 500 angstroms.

7. The device of claim 1 wherein the light emitting layer is In x Al y Ga 1−x−y N.

8. The device of claim 7 wherein the first element is aluminum.

9. The device of claim 7 wherein the first element is indium.

10. The device of claim 9 wherein a composition of aluminum in the light emitting layer is graded.

11. 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 quantum well and the second quantum well.

12. The device of claim 11 wherein a composition in the barrier layer is graded.

13. The device of claim 11 wherein the berrier layer comprises a first portion having a graded composition and a second portion having a substantially uniform composition.

14. The device of claim 13 wherein the first portion is located adjacent to one of the first and second quantum wells.

15. The device of claim 1 wherein the light emitting layer is Al x Ga −x N and the first element is aluminum.

16. A semiconductor light emitting device comprising a III-nitride light emitting layer disposed between an n-type region and a p-type region, the light emitting layer having a graded composition of a first element, wherein a change in composition of the first element in the light emitting layer is greater than 0.2% per angstrom and less than 1% per angstrom across a thickness of the light emitting layer, wherein the light emitting layer is a first portion of a III-nitride light emitting region, the light emitting region further comprising a second portion of uniform composition.

17. The device of claim 16 wherein the first portion has a thickness between 10 and 100 angstroms.

18. The device of claim 16 wherein the first portion is located at an end of the light emitting region closest to the n-type region.

19. The device of claim 16 wherein the first portion is located at an end of the light emitting region closest to the p-type region.

20. The device of claim 16 wherein:

the light emitting region further comprises a third portion, the third portion having a graded composition of a first element; and

the second portion is disposed between the first and third portions.