Seed selection and growth methods for reduced-crack group III nitride bulk crystals
In one instance, the invention provides a method of growing bulk crystal of group III nitride using a seed crystal selected by (a) measuring x-ray rocking curves of a seed crystal at more than one point, (b) quantifying the peak widths of the measured x-ray rocking curves, and (c) evaluating the distribution of the quantified peak widths. The invention also includes the method of selecting a seed crystal for growing bulk crystal of group III nitride. The bulk crystal of group III nitride can be grown in supercritical ammonia or a melt of group III metal using at least one seed selected by the method above.
1. A method of growing a bulk crystal of group III nitride having a composition of Ga x1 Al y1 In 1-x1-y1 N (0≦x1≦1, 0≦x1+y1≦1) comprising:
(a) measuring x-ray rocking curves of the seed crystal at more than one point;
(b) quantifying peak widths of the measured x-ray rocking curves;
(c) comparing a measure of the distribution of the quantified peak widths to an acceptable value; and
(d) growing single crystal Ga x1 Al y1 In 1-x1-y1 N on a face of the seed crystal having the acceptable value of the distribution of quantified peak widths to form the bulk crystal of group III nitride, wherein the bulk crystal of group III nitride has a crack density less than 1 cm −2 .
2. A method according to claim 1 wherein the method of quantifying the peak widths comprises calculating a full width half maximum of peaks of the x-ray rocking curves.
3. A method according to claim 1 wherein the distribution of the quantified peak widths is determined with a standard deviation.
4. A method according to claim 3 wherein the standard deviation is less than 30% of the mean value of the quantified peak widths.
5. A method according to claim 3 wherein the standard deviation is less than 20% of the mean value of the quantified peak widths.
6. A method according to claim 1 wherein the seed crystal is primarily c-plane oriented and the x-ray rocking curves are measured on one or more off-axis planes.
7. A method according to claim 6 , wherein the x-ray rocking curves are measured in m-direction.
8. A method according to claim 6 , wherein the off-axis plane is 201 reflection.
9. A method according to claim 6 , wherein the off-axis plane is 102 reflection.
10. A method according to claim 1 wherein the seed crystal is gallium nitride.
11. A method according to claim 10 wherein the group III nitride is GaN.
12. A method according to claim 1 wherein the group III nitride is grown in supercritical ammonia.
13. A method of selecting a seed crystal for growing bulk crystal of group III nitride having a composition of Ga x1 Al y1 In 1-x1-y1 N (0≦x1≦1, 0≦x1+y1≦1) comprising,
(a) measuring x-ray rocking curves of a seed crystal at more than one point;
(b) quantifying peak widths of the measured x-ray rocking curves;
(c) comparing a measure of the distribution of the quantified peak widths to an acceptable value; and
(d) designating the seed crystal as acceptable or unacceptable for growth of a bulk crystal of group III nitride having a crack density less than 1 cm −2 based on said measure of the distribution of quantified peak widths.
14. A method according to claim 13 wherein the method of quantifying the peak widths comprises calculating a full width half maximum of peaks of the x-ray rocking curves.
15. A method according to claim 13 wherein the distribution of the quantified peak widths is determined with a standard deviation.
16. A method according to claim 15 wherein the standard deviation is less than 30% of the mean value of the quantified peak widths.
17. A method according to claim 15 wherein the standard deviation is less than 20% of the mean value of the quantified peak widths.
18. A method according to claim 13 wherein the seed crystal is primarily c-plane oriented and the x-ray rocking curves are measured on one or more off-axis planes.
19. A method according to claim 18 , wherein the x-ray rocking curves are measured in the m-direction.
20. A method according to claim 18 , wherein the off-axis plane is 201 reflection.
21. A method according to claim 18 , wherein the off-axis plane is 102 reflection.
22. A method according to claim 13 wherein the seed crystal is gallium nitride.
23. A method according to claim 22 wherein the group III nitride is GaN.
24. A method according to claim 1 , wherein the bulk crystal has a thickness larger than 1 mm.
25. A method according to claim 12 , wherein the bulk crystal has a thickness larger than 1 mm.