Defects annealing and impurities activation in III-nitride compound
A GaN sample in a sealed enclosure is heated very fast to a high temperature above the point where GaN is thermodynamically stable and is then cooled down very fast to a temperature where it is thermodynamically stable. The time of the GaN exposure to a high temperature range above its thermodynamic stability is sufficiently short, in a range of few seconds, to prevent the GaN from decomposing. This heating and cooling cycle is repeated multiple times without removing the sample from the enclosure. As a result, by accumulating the exposure time in each cycle, the GaN sample can be exposed to a high temperature above its point of thermodynamic stability for a long time but the GaN sample integrity is maintained (i.e., the GaN doesn't decompose) due to the extremely short heating duration of each single cycle.
1. A process for annealing a III-nitride semiconductor without decomposing, the process including:
capping a III-nitride semiconductor sample with a cap made from a material that is thermodynamically stable at an annealing temperature;
positioning the capped III-nitride semiconductor sample inside an enclosure;
charging the enclosure with one of an inert gas, nitrogen, ammonia, and mixtures thereof at an applied gas pressure above one atmosphere; and
subjecting the capped III-nitride semiconductor sample to a plurality of heating and cooling cycles without removing the sample from the enclosure, each heating and cooling cycle including
(1) rapidly heating the sample for a duration of several seconds to a temperature T1 higher than a temperature Ts, Ts being a temperature above which the III-nitride semiconductor sample becomes thermodynamically unstable at the applied gas pressure; and
(2) rapidly cooling the sample for a duration of several seconds to a temperature T2, T2 being a temperature below Ts where the sample just becomes thermodynamically stable;
wherein during each heating and cooling cycle the sample is exposed to an elevated temperature range between Ts and T1 for a predetermined time period t1 without decomposing, t1 being less than a time t2 at which the sample would start to decompose at the elevated temperature range; and
wherein at the end of the plurality of heating and cooling cycles, the sample has been heated to a temperature in the elevated temperature range for a total cumulative time t3 greater than t2, without the sample decomposing.
2. The process according to claim 1 , wherein the cap comprises a III-nitride cap.
3. The process according to claim 2 , wherein the III-nitride cap is applied to the III-nitride semiconductor by means of MOCVD.
4. The process according to claim 1 , wherein the III-nitride semiconductor is GaN.
5. The process according to claim 4 , further comprising applying a thin AlN cap to the GaN.
6. The process according to claim 5 , wherein the AlN cap is applied to the GaN by means of MOCVD.
7. The process according to claim 6 , wherein the AlN cap is applied to the GaN by means of high temperature MOCVD at about 1000° C.
8. The process according to claim 7 , wherein the AlN cap has a thickness of about 2-10 nm.
9. The process according to claim 6 , wherein the AlN cap comprises a first layer of AlN deposited by MOCVD at a temperature of about 1000° C. and a second layer of AlN deposited by MOCVD at a temperature below 1000° C.
10. The process according to claim 4 , wherein the applied gas pressure is about 20 bar.
11. The process according to claim 10 , wherein the gas is nitrogen.
12. A process for annealing a III-nitride semiconductor without decomposing, the process including:
implanting a III-nitride semiconductor sample with a plurality of dopant ions to form a doped III-nitride semiconductor sample;
capping the doped III-nitride semiconductor sample with a cap made from a material that is thermodynamically stable at an annealing temperature;
positioning the capped doped III-nitride semiconductor sample inside an enclosure;
charging the enclosure with one of an inert gas, nitrogen, ammonia, and mixtures thereof at an applied gas pressure above one atmosphere; and
subjecting the capped doped III-nitride semiconductor sample to a plurality of heating and cooling cycles without removing the sample from the enclosure, each heating and cooling cycle including
(1) rapidly heating the sample for a duration of several seconds to a temperature T1 higher than a temperature Ts, Ts being a temperature above which the III-nitride semiconductor sample becomes thermodynamically unstable at the applied gas pressure; and
(2) rapidly cooling the sample for a duration of several seconds to a temperature T2, T2 being a temperature below Ts where the sample just becomes thermodynamically stable;
wherein during each heating, and cooling cycle the sample is exposed to an elevated, temperature range between Ts and T1 for a predetermined time period t1 without decomposing, t1 being, less than a time t2 at which the sample would start to decompose at the elevated temperature range; and
wherein at the end of the plurality of heating and cooling cycles, the sample has been heated to a temperature in the elevated temperature range for a total cumulative time t3 greater than t2, without the sample decomposing.
13. The process according to claim 12 , wherein the cap comprises a III-nitride cap.
14. The process according to claim 13 , wherein the III-nitride cap is applied to the III-nitride semiconductor by means of MOCVD.
15. The process according to claim 12 , wherein the cap is applied before implantation of the dopant ions.
16. The process according to claim 12 , wherein the cap is applied after implantation of the dopant ions.
17. The process according to claim 12 , further comprising annealing the sample at a temperature T3 below Ts before the beginning the first of the plurality of heating and cooling cycles.
18. The process according to claim 12 , wherein the III-nitride semiconductor is GaN.
19. The process according to claim 18 , further comprising applying an AlN cap to the GaN.
20. The process according to claim 19 , wherein the AlN cap is applied to the GaN by means of MOCVD before the implantation of the dopant ions.
21. The process according to claim 18 , wherein the AlN cap is applied to the GaN by means of high temperature MOCVD at about 1000° C.
22. The process according to claim 21 , wherein the AlN cap has a thickness of about 2-10 nm.
23. The process according to claim 22 , wherein the AlN cap comprises a first layer of AlN deposited by MOCVD at a temperature of about 1000° C. and a second layer of AlN deposited by MOCVD at a temperature below 1000° C.
24. The process according to claim 18 , wherein the GaN sample is implanted with Mg ions.
25. The process according to claim 24 , wherein after annealing, the GaN sample implanted with Mg ions shows high p-type conductivity with sheet resistance R SH below 9 kΩ/sq.
26. A product of the process of claim 1 .
27. A product of the process of claim 12 .
28. The process according to claim 1 , wherein the III-nitride semiconductor is one of GaN, InN, AN and their alloys.
29. The process according to claim 10 , wherein t1 is about 8 seconds.
30. The process according to claim 10 , wherein T1 is between about 1300° C. and about 1400° C.
31. The process according to claim 30 , further comprising heating and cooling the capped III-nitride semiconductor sample for 40 cycles, wherein t3 after the 40 cycles is about 5 minutes, 30 seconds.
32. The process according to claim 12 , wherein the cap is applied before the implantation of the dopant ions.
33. The process according to claim 17 , wherein T3=T2.
34. The process according to claim 18 , wherein the applied gas pressure is 20 bar.
35. The process according to claim 34 , wherein t1 is about 8 seconds.
36. The process according to claim 34 , wherein T1 is between about 1300° C. and about 1400° C.
37. The process according to claim 36 , further comprising heating and cooling the capped III-nitride semiconductor sample for 40 cycles, wherein t3 after the 40 cycles is about 5 minutes, 30 seconds.