Process for obtaining of bulk monocrystalline gallium-containing nitride
View Patent ↗The invention relates to new improvements in a process for crystal growth in the environment of supercritical ammonia-containing solution, which are based on use of specific azide mineralizers and result in the improved bulk Group XIII element nitride monocrystals, in particular balk monocrystalline gallium-containing nitride, intended mainly for variety of nitride-based semiconductor products such as various opto-electronic devices. The invention further relates to a mineralizer used for supercritical ammonia-containing solution which comprises at least one compound selected from the group consisting of LiN 3 , NaN 3 , KN 3 , and CsN 3 .
1. A process for obtaining a bulk gallium-containing nitride monocrystal, comprising:
contacting ammonia with a mineralizer comprising a Group I azide in a pressurized reaction vessel to form a supercritical ammonia-containing solution comprising an ion of a Group I element;
dissolving a gallium-containing feedstock at a dissolution temperature and pressure condition under which the gallium feedstock dissolves in the supercritical ammonia-containing solution; and
crystallizing a gallium-containing nitride on a surface of a seed at a crystallization temperature and pressure condition,
wherein the crystallization temperature and pressure condition is determined using a temperature coefficient of solubility and a pressure coefficient of solubility of the gallium-containing nitride to be crystallized.
2. The process according to claim 1 , wherein gaseous nitrogen, produced during decomposition of the azide, is at least partially evacuated before the crystallizing step is started.
3. The process according to claim 1 , wherein the crystallized gallium-containing nitride has a general formula Al x Ga 1-x N, where 0≦x<1.
4. The process according to claim 1 , wherein the mineralizer is selected from the group consisting of LiN 3 , NaN 3 , KN 3 , CsN 3 and mixtures thereof.
5. The process according to claim 4 , wherein the mineralizer contains at least one compound selected from the group consisting of LiN 3 , NaN 3 , KN 3 and CsN 3 .
6. The process according to claim 5 , wherein the mineralizer contains NaN 3 and KN 3 .
7. The process according to claim 5 , wherein the mineralizer contains NaN 3 and LiN 3 .
8. The process according to claim 5 , wherein the mineralizer contains KN 3 and LiN 3 .
9. The process according to claim 5 , wherein the mineralizer further contains Group I element-containing compound other than azide.
10. A process according to claim 9 , wherein the mineralizer further comprises a Group II element-containing compound other than an azide.
11. The process according to claim 1 , wherein the Group I azide is added in a molar ratio of azide to ammonia ranging from 1:200 to 1:2.
12. The process according to claim 1 , wherein the seed comprises a crystalline layer of Group XIII element-containing nitride having a dislocation density less than 10 7 /cm 2 .
13. The process according to claim 1 , wherein the seed comprises a structure having a number of surfaces spaced apart from each other, arranged on a primary substrate and susceptible to a lateral overgrowth of a crystalline nitride.
14. The process according to claim 1 , wherein a monocrystalline nitride layer that is obtained has the same or better quality as the gallium-containing nitride monocrystal gets thicker.
15. The process according to claim 13 , wherein the seed contains the primary substrate made of a crystalline nitride of Group XIII element.
16. The process according to claim 15 , wherein the seed contains the primary substrate made of gallium nitride.
17. The process according to claim 15 , wherein the seed contains the primary substrate made of a crystalline material such as sapphire, spinel, ZnO, SiC or Si, and wherein the primary substrate made of a material reactive to a supercritical ammonia-containing solution is covered with a protective layer prior to formation of a monocrystalline nitride layer.
18. A process according to claim 17 , wherein the protective layer comprises a Group XIII element-containing nitride or a metallic Ag.
19. The process according to claim 1 , wherein the bulk nitride monocrystal obtained consists essentially of gallium nitride.
20. The process according to claim 1 , wherein the bulk nitride monocrystal obtained contains any of the following elements: Ni, Cr, Co, Ti, Fe, Al, Ag, Mo, W, Si and Mn.
21. The process according to claim 1 , wherein a surface of the seed is covered with a mask layer prior to formation of a monocrystalline nitride layer.
22. A process according to claim 1 , wherein the mineralizer further comprises a Group II azide and the supercritical ammonia-containing solution further comprises an ion of a Group II element.
23. A process for obtaining a bulk gallium-containing nitride monocrystal, comprising:
contacting ammonia with a mineralizer comprising a Group I azide in a pressurized reaction vessel at a condition under which a gallium-containing nitride has a negative temperature coefficient of solubility and a positive pressure coefficient of solubility, forming a supercritical ammonia-containing solution comprising an ion of a Group I element;
dissolving a gallium-containing feedstock at a dissolution temperature and pressure condition under which the gallium-containing feedstock dissolves in the supercritical ammonia-containing solution;
obtaining a super-saturation of the supercritical ammonia-containing solution at a crystallization temperature and pressure condition having a temperature higher than that of the dissolution temperature and pressure condition or a pressure lower than that of the dissolution temperature and pressure condition; and
crystallizing a gallium-containing nitride on a surface of a seed by maintaining the super-saturation of the supercritical ammonia-containing solution at the level at which spontaneous crystallization of nitride is negligible.
24. A process according to claim 2 , wherein the mineralizer further comprises a Group II azide and the supercritical ammonia-containing solution further comprises an ion of a Group II element.
25. A method for creating an epitaxial layer on a nitride monocrystal, comprising:
contacting ammonia with a mineralizer comprising a Group I azide in a pressurized reaction vessel to form a supereritical ammonia-containing solution comprising an ion of a Group I element;
dissolving a gallium-containing feedstock at a dissolution temperature and pressure condition under which the gallium feedstock dissolves in the supereritical ammonia-containing solution;
crystallizing a gallium-containing nitride on a surface of a seed at a crystallization temperature and pressure condition to obtain a nitride monocrystal,
wherein the crystallization temperature and pressure condition is determined using a temperature coefficient of solubility and a pressure coefficient of solubility of the gallium-containing nitride to be crystallized; and
growing an epitaxial layer on the nitride monocrystal.
26. The method of claim 25 , wherein the bulk nitride monocrystal has at least one epitaxial layer of the same or different Group XIII element-containing nitride, deposited by a MOCVD, HVPE or MBE method as a template for opto-electronic devices.
27. The method of claim 26 , wherein the epitaxial layer is doped with one or more dopants.