Substrate for epitaxy

• US 20040261692A1
• Filed: 04/26/2004
• Published: 12/30/2004
• Est. Priority Date: 10/26/2001
• Status: Active Grant

• Current Assignee: Ammono Sp. Z O.O., Nichia Corporation
• Original Assignee: Ammono Sp. Z O.O., Nichia Corporation
• Inventors: Kanbara, Yasuo, Doradzinski, Roman, Garczynski, Jerzy, Dwilinski, Robert, Sierzputowski, Leszek P.
• Granted Patent: US 7,132,730 B2
• Time in Patent Office: Days
• US Class Current: 117/84
• CPC Class Codes: C30B 29/40 AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
• CPC Class Codes: C30B 29/403 AIII-nitrides
• CPC Class Codes: C30B 29/406 Gallium nitride
• CPC Class Codes: C30B 7/00 Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions from molten solvents C30B9/00; by normal or gradient freezing C30B11/00; under a protective fluid C30B27/00
• CPC Class Codes: C30B 7/10 by application of pressure, e.g. hydrothermal processes
• CPC Class Codes: H01S 5/0281 Coatings made of semiconductor materials
• CPC Class Codes: H01S 5/32341 blue laser based on GaN or GaP

Abstract

The invention relates to a substrate for epitaxy, especially for preparation of nitride semiconductor layers. Invention covers a bulk nitride mono-crystal characterized in that it is a mono-crystal of gallium nitride and its cross-section in a plane perpendicular to c-axis of hexagonal lattice of gallium nitride has a surface area greater than 100 mm², it is more than 1.0 μm thick and its C-plane surface dislocation density is less than 10⁶/cm², while its volume is sufficient to produce at least one further-processable non-polar A-plane or M-plane plate having a surface area at least 100 mm². More generally, the present invention covers a bulk nitride mono-crystal which is characterized in that it is a mono-crystal of gallium-containing nitride and its cross-section in a plane perpendicular to c-axis of hexagonal lattice of gallium-containing nitride has a surface area greater than 100 mm², it is more 1.0 μm thick and its surface dislocation density is less than 10⁶/cm². Mono-crystals according to the present invention are suitable for epitaxial growth of nitride semiconductor layers. Due to their good crystalline quality they are suitable for use in opto-electronics for manufacturing opto-electronic semiconductor devices based on nitrides, in particular for manufacturing semiconductor laser diodes and laser devices. The a.m bulk mono-crystals of gallium-containing nitride are crystallized on seed crystals. Various seed crystals may be used. The bulk mono-crystals of gallium-containing nitride are crystallized by a method involving dissolution of a gallium-containing feedstock in a supercritical solvent and crystallization of a gallium nitride on a surface of seed crystal, at temperature higher and/or pressure lower than in the dissolution process.

Claims

1. A bulk nitride mono-crystal comprising a mono-crystal of gallium nitride and its cross-section in a plane perpendicular to a c-axis of a hexagonal lattice of gallium nitride has a surface area greater than 100 mm², the mono-crystal having a thickness greater than 1.0 μ

m thick and a C-plane surface dislocation density less than 10⁶/cm², and having a volume sufficient to produce at least one further-processable non-polar A-plane or M-plane plate having a surface area of at least 100 mm².

2. A bulk nitride mono-crystal according to claim 1, wherein its quality does not deteriorate with thickness.

3. A bulk nitride mono-crystal according to claim 1, wherein it contains also elements of Group I (IUPAC 1989).

4. A bulk nitride mono-crystal according to claim 1, wherein it contains also elements such as Ti, Fe, Co, Cr and Ni.

5. A bulk nitride mono-crystal according to claim 1, wherein additionally it contains donor and/or acceptor and/or magnetic dopants in concentrations from 10¹⁷/cm³ to 10²¹/cm³.

6. A bulk nitride mono-crystal according to claim 1, wherein it is crystallized on a surface of a seed crystal.

7. A bulk nitride mono-crystal according to claim 6, wherein a seed crystal is a gallium-nitride seed crystal.

8. A bulk nitride mono-crystal according to claim 7, wherein a seed is in form of a flat plate with two parallel faces perpendicular to c-axis of hexagonal lattice of gallium nitride, while the bulk mono-crystal of gallium nitride is crystallized on the nitrogen-terminated (000-1) face of the seed only, the gallium-terminated (0001) face being blocked in order to prevent growth of gallium nitride mono-crystal thereon.

9. A bulk nitride mono-crystal according to claim 6, wherein a seed crystal is a hetero-seed made of sapphire, silicon carbide or the like, with a top nitride buffer layer at least on its C-plane, consisting essentially of gallium nitride, and the bulk nitride mono-crystal is crystallized on the buffer layer, while at least one, preferably all the remaining surfaces of the hereto-seed are covered with a protective mask.

10. A bulk nitride mono-crystal according to claim 6, wherein it is crystallized on a plurality of surfaces susceptible for lateral growth of the nitride, the surfaces being spaced apart from each other and the remaining surfaces of the seed crystal are covered with a protective mask.

11. A bulk nitride mono-crystal according to claim 1, wherein its surface dislocation density on nitrogen-terminated face is close to 10⁴/cm² and at the same time the full width at half maximum (FWHM) of the X-ray rocking curve is close to 60 arcsec.

40. A bulk nitride mono-crystal according to claim 1, wherein it is obtained by a method involving dissolution of a respective Group XIII (IUPAC, 1989) elements feedstock in a supercritical solvent, with over-saturation of the supercritical solution with respect to the desired gallium-containing nitride being reached by means of temperature gradient and/or pressure change and crystallization of a desired gallium-containing nitride on a surface of seed crystal.

41. A bulk nitride mono-crystal according to claim 40, wherein the supercritical solvent contains NH₃ and/or its derivatives, and includes ions of elements of Group I (IUPAC 1989)—

at least potassium or sodium ions, the feedstock consists essentially of gallium-containing nitride and/or its precursors, selected from a group including azides, imides, amido-imides, amides, hydrides, gallium-containing metal compounds and alloys, as well as metallic Group XIII (IUPAC,

     1989) elements, especially metallic gallium.

42. A bulk nitride mono-crystal according to claim 41, wherein in the process in which it is obtained crystallization of gallium-containing nitride takes place in an autoclave, at temperatures from 100°

C. to 800°

C. and at pressures from 10 MPa to 1000 MPa and a molar ratio of ions of elements of GROUP I (IUPAC

     1989) to the remaining components of the supercritical solvent ranges from 1;

200 to 1;

2.

43. A bulk nitride mono-crystal according to claim 41, wherein as a source of alkali metal ions alkali metals or alkali metal compounds, excluding those containing halogens, are used.

44. A bulk nitride mono-crystal according to claim 41, wherein its crystallization is controlled by means of adjusting temperature and pressure of dissolution step and temperature and pressure of crystallization step.

45. A bulk nitride mono-crystal according to claim 44, wherein it is crystallized at temperature ranging from 400 to 600°

C.

46. A bulk nitride mono-crystal according to claim 41, wherein it is crystallized in an autoclave with two separated zones, dissolution zone and crystallization zone, and with a temperature difference between the two zones during crystallization not higher than 150°

C., preferably not higher than 100°

C.

47. A bulk nitride mono-crystal according to claim 46, wherein it is crystallized while controlling over-saturation of supercritical solution in the crystallization zone of the autoclave with the two separated zones, and maintaining a predetermined temperature difference between the two zones by using a baffle or baffles separating the two zones, in order to control a chemical (mass) transport between the two zones.

48. A bulk nitride mono-crystal according to claim 46, wherein control of over-saturation of supercritical solution in the crystallization zone of the autoclave with two separate zones and with a predetermined temperature difference between the two zones—

is achieved by means of using a feedstock material containing gallium in a form of a corresponding nitride crystals having a total surface area higher than a total surface area of seed crystals used.

51. A bulk nitride mono-crystal according to claim 1, wherein it is suitable for epitaxial growth of nitride semiconductor layers.

52. Use of a bulk nitride mono-crystal according to claim 1, as a substrate for epitaxy.

53. Use according to claim 52, wherein a substrate for epitaxy has a form of c-oriented GaN bulk mono-crystal of 2-inch diameter.

54. Use according to claim 52, wherein a substrate for epitaxy has a form of A- or M-plane gallium-containing nitride mono-crystal plate having a further-processable surface area of at least 100 mm².

55. Use according to claim 52, wherein a substrate for epitaxy has a form of A- or M-plane GaN mono-crystal plate having a further-processable surface area of at least 100 mm².

12. A bulk nitride mono-crystal wherein it is a mono-crystal of gallium-containing nitride and its cross-section in a plane perpendicular to c-axis of hexagonal lattice of gallium-containing nitride has a surface area greater than 100 mm², it is more than 1.0 μ

m thick and its surface dislocation density is less than 10⁶/cm².

13. A bulk nitride mono-crystal according to claim 12, wherein it is essentially flat so that its curving is less than 20 micron.

14. A bulk nitride mono-crystal according to claim 12, wherein it has a high value of more than 10E5 Q/cm² in a sheet resistance, preferably more 10E7 Q/cm².

15. A bulk nitride mono-crystal according to claim 12, wherein it is at least 100 μ

m thick.

16. A bulk nitride mono-crystal according to claim 15, wherein its volume is sufficient to produce at least one further-processable non-polar A-plane or M-plane plate having a surface area at least 100 mm².

17. A bulk nitride mono-crystal according to claim 12, wherein it has a surface area greater than 2 cm², preferably greater than 5 cm² in form of a flat plane perpendicular to c-axis of its hexagonal lattice.

18. A bulk nitride mono-crystal according to claim 12, wherein its quality does not deteriorate with thickness.

19. A bulk nitride mono-crystal according to claim 12, characterized in that it contains also elements of Group I (IUPAC 1989).

20. A bulk nitride mono-crystal according to claim 12, characterized in that it contains also elements such as Ti, Fe, Co, Cr and Ni.

21. A bulk nitride mono-crystal according to claim 12, wherein additionally it contains donor and/or accepter and/or magnetic dopants in concentrations from 10¹⁷/cm³ to 10²¹/cm³.

22. A bulk nitride mono-crystal according to claim 12, wherein it is crystallized on a surface of a seed crystal.

23. A bulk nitride mono-crystal according to claim 22, wherein a seed crystal is a gallium-containing nitride seed crystal.

24. A bulk nitride mono-crystal according to claim 23, wherein a seed crystal has the same composition as the bulk nitride mono-crystal.

25. A bulk nitride mono-crystal according to claim 24, wherein both a seed crystal and the bulk nitride mono-crystal consist essentially of gallium nitride.

26. A bulk nitride mono-crystal according to claim 22, wherein a seed crystal is a hetero-seed made of sapphire, silicon carbide or the like, with a top nitride buffer layer at least on its one side and the bulk nitride mono-crystal is crystallized on the buffer layer, while at least one, preferably all the remaining surfaces of the hetero-seed are covered with a protective mask.

27. A bulk nitride mono-crystal according to claim 26, wherein a top nitride buffer layer and the bulk nitride mono-crystal crystallized on the buffer layer consist essentially of gallium nitride.

28. A bulk nitride mono-crystal according to claim 22, wherein it is crystallized on a plurality of surfaces susceptible for lateral growth of the nitride, the surfaces being spaced apart from each other and the remaining surfaces of the seed crystal are covered with a protective mask.

29. A bulk nitride mono-crystal according to claim 22, wherein it is crystallized on a homo-seed crystal in form of a plate with two parallel planes essentially perpendicular to c-axis of its hexagonal lattice and the bulk mono-crystal is crystallized on all surfaces of the seed crystal.

30. A bulk nitride mono-crystal according to claim 29, wherein a seed and the bulk nitride mono-crystal consist essentially of gallium nitride and the seed is an form of a flat plate with two parallel faces perpendicular to c-axis of hexagonal lattice of gallium-containing nitride, (0001) and (000-1), while two bulk mono-crystals of gallium nitride are crystallized on both such faces of the seed crystal.

31. A bulk nitride mono-crystal according to claim 30, wherein it is crystallized on a seed with one of the faces perpendicular to c-axis of hexagonal lattice of gallium-containing nitride, (0001) or (000-1), covered by metallic plate made preferably of silver.

32. A bulk nitride mono-crystal according to claim 30, wherein it is crystallized on a seed with one of the faces perpendicular to c-axis of hexagonal lattice of gallium-containing nitride, (0001) or (000-1), coated by metallic layer, preferably made of silver.

33. A bulk nitride mono-crystal according to claim 30, wherein it is crystallized on a seed with one of the faces perpendicular to c-axis of hexagonal lattice of gallium-containing nitride, (0001) or (000-1), blocked by arranging on that plane of the seed a second seed crystal of the same size with the same face:

(0001) or (000-1) facing the corresponding face to be blocked of the first seed.

34. A bulk nitride mono-crystal according to claim 31, in that wherein it is crystallized on nitrogen-terminated (000-1) face of the seed only.

35. A bulk nitride mono-crystal according to claim 34, wherein it has a better surface quality than a bulk mono-crystal that can be crystallized on gallium-terminated (0001) face of the seed crystal.

36. A bulk nitride mono-crystal according to claim 34, wherein it has lower surface dislocation density than a bulk mono-crystal that can be crystallized on gallium-terminated (0001) face of the seed crystal.

37. A bulk nitride mono-crystal according to claim 34, wherein it has a better electrical resistivity than a bulk mono-crystal that can be crystallized on gallium-terminated (0001) face of the seed crystal.

38. A bulk nitride mono-crystal according to claim 34, wherein it has lower values of full width at half maximum (FWHM) of the X-ray rocking curve than a bulk mono-crystal that can be crystallized on gallium-terminated (0001) face of the seed crystal.

39. A bulk nitride mono-crystal according to claim 34, wherein its surface dislocation density on nitrogen-terminated face is close to 10⁴/cm² and at the same time the FWHM of the X-ray rocking curve is close to 60 arcsec.

49. A bulk nitride mono-crystal grown in a direction parallel to c-axis of hexagonal lattice of gallium nitride seed in a supercritical NH₃ containing gallium-complex compounds at Ga:

NH₃ molar ratio of more than 1;

50, in order to have a thickness high enough to obtain at least one further-processable A-plane or M-plane gallium-nitride substrate.

50. A bulk nitride mono-crystal grown on a seed having no substantial tilted crystal axis by means of a supercritical NH₃ containing gallium-complex compounds, having not so much surface roughness as to decrease lifetime of a nitride semiconductor device formed thereon.