III-nitride light emitting devices grown on templates to reduce strain
View Patent ↗In a III-nitride light emitting device, the device layers including the light emitting layer are grown over a template designed to reduce strain in the device, in particular in the light emitting layer. Reducing the strain in the light emitting device may improve the performance of the device. The template may expand the lattice constant in the light emitting layer over the range of lattice constants available from conventional growth templates. Strain is defined as follows: a given layer has a bulk lattice constant a bulk corresponding to a lattice constant of a free standing material of a same composition as that layer and an in-plane lattice constant a in-plane corresponding to a lattice constant of that layer as grown in the structure. The amount of strain in a layer is |(a in-plane −a bulk )|/a bulk . In some embodiments, the strain in the light emitting layer is less than 1%.
1. A device comprising: a III-nitride structure comprising:
a first layer, wherein the first layer is substantially free of indium;
a second layer grown over the first layer, wherein the second layer is a non-single crystal layer comprising indium;
a third layer disposed between the first layer and the second layer and in direct contact with the first layer, wherein the third layer is a non-single crystal layer substantially free of indium; and
device layers grown over the second layer, the device layers comprising a III-nitride light emitting layer disposed between an n-type region and a p-type region.
2. The device of claim 1 wherein the first layer is GaN and the second layer is InGaN.
3. The device of claim 1 further comprising a layer having a graded composition disposed between the light emitting layer and the first layer.
4. A The device comprising: a III-nitride structure comprising:
a first layer, wherein the first layer is substantially free of indium;
a second layer grown over the first layer, wherein the second layer is a non- single crystal layer comprising indium;
device layers grown over the second layer, the device layers comprising a III- nitride light emitting layer disposed between an n-type region and a p-type region; and
a third layer disposed between the second layer and the light emitting layer and in direct contact with the second layer, wherein the third layer is a non-single crystal layer comprising indium.
5. The device of claim 1 wherein the light emitting layer is doped with silicon to a dopant concentration between 1×10 18 cm −3 and 1×10 20 cm −3 .
6. The device of claim 1 wherein the structure is grown over a surface of a substrate which is tilted from a major crystallographic plane of the substrate by at least 0.1°.
7. The device of claim 1 wherein the light emitting layer has a thickness greater than 15 angstroms.
8. The device of claim 1 wherein the light emitting layer has a thickness greater than 50 angstroms.
9. The device of claim 1 wherein the light emitting layer is doped with silicon to a dopant concentration between 1×10 18 cm −3 and 1×10 20 cm −3 .
10. The device of claim 1 further comprising:
contacts electrically connected to the n-type region and the p-type region; and
a cover disposed over the III-nitride structure.
11. A device comprising: a III-nitride structure comprising:
a first layer, wherein the first layer is substantially free of indium;
a second layer grown over the first layer, wherein the second layer is a non-single crystal layer comprising indium;
device layers grown over a second layer, the device layers comprising a III-nitride light emitting layer disposed between an n-type region and a p-type region; and
a third layer disposed between the second layers and the light emitting layer and in direct contact with the second layer, wherein the third layer is a non-single crystal layer comprising indium.
12. The device of claim 11 wherein the second layer has a different indium composition than the third layer.
13. A device comprising:
a first substantially single crystal layer;
a second substantially single crystal layer; and
a non-single crystal layer comprising indium disposed between the first and second substantially single crystal layers.
14. The device of claim 13 wherein the III-nitride structure further comprises a light emitting layer disposed between an n-type region and a p-type region, wherein the second substantially single crystal layer is disposed between the light emitting region and the non-single crystal layer.
15. The device of claim 14 wherein a composition of the first substantially single crystal layer is different from a composition of the second substantially single crystal layer.
16. The device of claim 14 wherein:
the first substantially single crystal layer is GaN or InGaN;
the second substantially single crystal layer is InGaN; and
the second substantially single crystal layer has a larger InN composition that the first substantially single crystal layer.
17. The device of claim 14 wherein the second substantially single crystal layer has a larger in-plane a-lattice constant than the first substantially single crystal layer.
18. The device of claim 14 wherein the non-single crystal layer is InGaN.
19. The device of claim 14 further comprising a third substantially single crystal layer disposed between the first substantially single crystal layer and the non-single crystal layer.
20. The device of claim 14 further comprising a third substantially single crystal layer disposed between the non-single crystal layer comprising indium and the light emitting layer.
21. The device of claim 14 wherein:
the light emitting layer has bulk lattice constant a bulk corresponding to a lattice constant of a free standing material of a same composition as the light emitting layer;
the light emitting layer has an in-plane lattice constant a in-plain corresponding to a lattice constant of the light emitting layer as grown in the structure; and
|(a in-plane −a bulk )|/a bulk in the light emitting layer is less than 1%.
22. The device of claim 14 wherein the light emitting layer has an a-lattice constant greater than 3.189 angstroms.
23. The device of claim 14 wherein the structure is grown over a surface of a substrate which is tilted from a major crystallographic plane of the substrate by at least 0.1°.
24. The device of claim 14 wherein the light emitting layer has a thickness greater than 50 angstroms.
25. The device of claim 14 wherein the light emitting layer has a thickness greater than 15 angstroms.
26. The device of claim 14 wherein the light emitting layer is doped with silicon to a dopant concentration between 1×10 18 cm −3 and 1×10 20 cm −3 .
27. The device of claim 14 further comprising:
contacts electrically connected to the n-type region and the p-type region; and
a cover disposed over the III-nitride structure.
28. A device comprising:
a III-nitride structure comprising a light emitting layer disposed between an n-type region and a p-type region, wherein:
a threading dislocation density in the light emitting layer is less than 3×10 9 cm −2 ; and
an a-lattice constant in the light emitting layer is greater than 3.200 Å.