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 method comprising:
growing a III-nitride structure on a substrate, the III-nitride structure comprising:
a template comprising:
a first layer grown directly on the substrate, the first layer being substantially free of indium;
a first substantially single crystal layer grown over the first layer;
a second layer grown over the first substantially single crystal layer,
wherein the second layer is a non-single crystal layer comprising indium; and
device layers grown over the template, the device layers comprising a III-nitride light emitting layer disposed between an n-type region and a p-type region.
2. The method of claim 1 wherein the template further comprises a second substantially single crystal layer grown over the second layer.
3. The method of claim 2 wherein the first substantially single crystal layer is a GaN layer and the second substantially single crystal layer is an InGaN layer with an InN composition between 0.50% and 20%.
4. The method of claim 2 wherein the second substantially single crystal layer is one of GaN, InGaN, AlGaN, and AIInGaN.
5. The method of claim 2 wherein the template further comprises:
a third layer grown over the second substantially single crystal layer, wherein the third layer is a non-single crystal layer comprising indium; and
a third substantially single crystal layer grown over the third layer.
6. The method of claim 2 wherein the template further comprises:
a third substantially single crystal layer disposed between the first layer and the second layer.
7. The method of claim 6 wherein a bulk lattice constant of a material of a same composition as the third substantially single crystal layer is larger than a bulk lattice constant of a material of a same composition as the first substantially single crystal layer.
8. The method of claim 6 wherein an InN composition in the second substantially single crystal layer is greater than an InN composition in the third substantially single crystal layer.
9. The method of claim 6 wherein a difference between a growth temperature of the third substantially single crystal layer and a growth temperature of the second layer is at least 350 ° C.
10. The method of claim 6 wherein a difference between a growth temperature of the second substantially single crystal layer and a growth temperature of the second layer is at least 250° C.
11. The method of claim 2 wherein the template further comprises:
a third substantially single crystal layer disposed between the second layer and the light emitting layer.
12. The method of claim 11 wherein an InN composition in the second substantially single layer is greater than an InN composition in the third substantially single crystal layer.
13. The method of claim 11 wherein an InN composition in the second substantially single layer is less than an InN composition in the third substantially single crystal layer.
14. The method of claim 1 wherein the second layer has a carbon content between 1×10 18 cm −3 and 1×10 20 cm −3 .
15. The method of claim 1 wherein the second layer has a defect density parallel to an interface disposed between the second layer and the device layers between 1×10 2 cm −1 and 1×10 7 cm −1 .
16. The method of claim 1 wherein one of the second layer, a layer directly above the second layer, and a layer directly below the second layer, has a defect density parallel to an interface disposed between the device layers and the first substantially single crystal layer between 1×10 2 cm −1 and 1×10 7 cm −1 .
17. The method of claim 1 further comprising:
connecting the III-nitride structure to a mount; and
removing the growth substrate.
18. The method of claim 17 further comprising removing a part of the template after removing the growth substrate.
19. The method of claim 1 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-plane 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%.
20. The method of claim 1 wherein an a-lattice constant of the light emitting layer is greater than 3.189 angstroms.
21. The method of claim 1 wherein the structure is grown on a surface of the substrate which is tilted from a major crystallographic plane of the substrate by at least 0.1° C.
22. The method of claim 1 wherein the light emitting layer has a thickness greater than 50 angstroms.
23. The method of claim 1 wherein the light emitting layer has a thickness greater than 15 angstroms.
24. The method 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 .
25. The method of claim 1 further comprising:
forming contacts electrically connected to the n-type region and the p-type region; and
disposing a cover over the III-nitride structure.
26. The method of claim 1 wherein:
the first layer is a non-single crystal GaN layer having a thickness less than 500 angstroms;
the first substantially single crystal layer is GaN or AIInGaN and has a thickness greater than 500 angstroms; and
the second layer is a non-single crystal InGaN layer having a thickness less than 500 angstroms and an InN composition greater than 0 and less than 20%.
27. The method of claim 1 wherein a difference between a growth temperature of the first substantially single crystal layer and a growth temperature of the second layer is at least 300° C.
28. The method of claim 1 wherein the template further comprises:
a second substantially single crystal layer disposed between the first layer and the second layer;
wherein a bulk lattice constant of a material of a same composition as the second substantially single crystal layer is larger than a bulk lattice constant of a material of a same composition as the first substantially single crystal layer.
29. A method comprising:
growing 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.