Nitride crystal with removable surface layer and methods of manufacture
View Patent ↗A nitride crystal or wafer with a removable surface layer comprises a high quality nitride base crystal, a release layer, and a high quality epitaxial layer. The release layer has a large optical absorption coefficient at wavelengths where the base crystal is substantially transparent and may be etched under conditions where the nitride base crystal and the high quality epitaxial layer are not. The high quality epitaxial layer may be removed from the nitride base crystal by laser liftoff or by chemical etching after deposition of at least one epitaxial device layer. The nitride crystal with a removable surface layer is useful as a substrate for a light emitting diode, a laser diode, a transistor, a photodetector, a solar cell, or for photoelectrochemical water splitting for hydrogen generation.
1. A nitride crystal with a removable surface layer, comprising:
a high quality nitride base crystal, comprising a nitrogen species and having a surface dislocation density below 10 5 cm −2 ;
a release layer having an optical absorption coefficient greater than 1000 cm −1 at least one wavelength where the high quality nitride base crystal is substantially transparent, with an optical absorption coefficient less than 50 cm −1 , the release layer being disposed on the nitride base crystal; and
a high quality epitaxial layer, between 0.05 micron and 500 microns thick, comprising nitrogen and having a surface dislocation density below 10 5 cm −2 , the epitaxial layer being disposed on the release layer.
2. The nitride crystal of claim 1 , wherein the thickness of the high quality epitaxial layer is between about 1 micron and about 50 microns.
3. The nitride crystal of claim 1 , wherein the dislocation density of the high quality nitride base crystal and of the high quality epitaxial layer is below 10 4 cm −2 .
4. The nitride crystal of claim 3 , wherein the dislocation density of the high quality nitride base crystal and of the high quality epitaxial layer is below 10 3 cm −2 .
5. The nitride crystal of claim 4 , wherein the dislocation density of the high quality nitride base crystal and of the high quality epitaxial layer is below 10 2 cm −2 .
6. The nitride crystal of claim 1 , wherein the surface orientation of the high quality epitaxial layer is within 5 degrees of {1 −1 0 0}.
7. The nitride crystal of claim 1 , wherein the surface orientation of the high quality epitaxial layer is within 5 degrees of {1 1 −2 0}.
8. The nitride crystal of claim 1 , wherein the surface orientation of the high quality epitaxial layer is within 5 degrees of {1 −1 0 ±1}.
9. The nitride crystal of claim 1 , wherein the surface orientation of the high quality epitaxial layer is within 5 degrees of {1 −1 0 ±2}.
10. The nitride crystal of claim 1 , wherein the surface orientation of the high quality epitaxial layer is within 5 degrees of {1 −1 0 ±3}.
11. The nitride crystal of claim 1 , wherein the surface orientation of the high quality epitaxial layer is within 5 degrees of {2 −2 0 ±1}.
12. The nitride crystal of claim 1 , wherein the surface orientation of the high quality epitaxial layer is within 5 degrees of {1 1 −2 ±2}.
13. The nitride crystal of claim 1 , wherein the nitride base crystal and the epitaxial layer comprise an Al x In y Ga l-x-y N layer, where 0≦x, y, x+y≦1.
14. The nitride crystal of claim 1 , wherein the release layer comprises Al x In y Ga l-x-y N, where 0≦x, y, x+y≦1, and at least one impurity.
15. The nitride crystal of claim 14 , wherein the at least one impurity comprises cobalt.
16. The nitride crystal of claim 1 , wherein the release layer comprises nitrogen and at least element selected from Si, Sc, Ti, V, Cr, Y, Zr, Nb, Mo, a rare earth element, Hf, Ta, and W.
17. The nitride crystal of claim 16 , wherein the release layer comprises nitrogen and chromium.
18. The nitride crystal of claim 1 , wherein the release layer has an optical absorption coefficient greater than 5000 cm −1 at least one wavelength where the base crystal has an optical absorption coefficient less than 5 cm −1 .
19. The nitride crystal of claim 1 , wherein the high quality epitaxial layer is between one and five microns thick.
20. The nitride crystal of claim 1 , wherein the base crystal, the release layer, and the high quality epitaxial layer are substantially free of voids.
21. The nitride crystal of claim 1 , wherein the release layer comprises a gallium and indium containing species.
22. The nitride crystal of claim 1 , wherein the release layer is substantially black in color.
23. A nitride crystal with a release layer, comprising:
a high quality Al x In y Ga l-x-y N base crystal, where 0≦x, y, x+y≦1, having a surface dislocation density below 10 5 cm −2 ; and
a release layer comprising Al x In y Ga l-x-y N and at least one impurity, where 0≦x, y, x+y≦1, having an optical absorption coefficient greater than 1000 cm −1 at at least one wavelength where the base crystal is substantially transparent, with an optical absorption coefficient less than 50 cm −1 , the release layer being disposed on the base crystal.
24. The nitride crystal of claim 23 , wherein the at least one impurity comprises cobalt.
25. The nitride crystal of claim 23 , wherein the dislocation density of the high quality nitride base crystal and of the release layer is below 10 4 cm −2 .
26. The nitride crystal of claim 25 , wherein the dislocation density of the high quality nitride base crystal and of the release layer is below 10 3 cm −2 .
27. The nitride crystal of claim 26 , wherein the dislocation density of the high quality nitride base crystal and of the release layer is below 10 2 cm −2 .
28. The nitride crystal of claim 23 , wherein the surface orientation of the release layer is within 5 degrees of {1 −1 0 0}.
29. The nitride crystal of claim 23 , wherein the surface orientation of the release layer is within 5 degrees of {1 1 −2 0}.
30. The nitride crystal of claim 23 , wherein the surface orientation of the release layer is within 5 degrees of {1 −1 0 ±1}.
31. The nitride crystal of claim 23 , wherein the surface orientation of the release layer is within 5 degrees of {1 −1 0 ±2}.
32. The nitride crystal of claim 23 , wherein the surface orientation of the release layer is within 5 degrees of {1 −1 0 ±3}.
33. The nitride crystal of claim 23 , wherein the surface orientation of the release layer is within 5 degrees of {2 −2 0 ±1}.
34. The nitride crystal of claim 23 , wherein the surface orientation of the release layer is within 5 degrees of {1 1 −2 ±2}.
35. The nitride crystal of claim 23 , wherein the release layer has an optical absorption coefficient greater than 5000 cm −1 at at least one wavelength where the base crystal has an optical absorption coefficient less than 5 cm −1 .
36. The nitride crystal of claim 23 , wherein the release layer is substantially black in color.
37. The nitride crystal of claim 23 , wherein the strain in either or both of the a or c lattice constants of the epitaxial release layer, with respect to those of the base nitride crystal, is less than 0.01% an 0.02%.