High-efficiency light-emitting element

• US 7,355,210 B2
• Filed: 02/21/2005
• Issued: 04/08/2008
• Est. Priority Date: 03/24/2004
• Status: Active Grant

• Current Assignee: Epistar Corporation (Ennostar, Inc.)
• Original Assignee: Epistar Corporation (Ennostar, Inc.)
• Inventors: Lin, Ting-Yang, Chang, Jia-Rong, Lai, Shih-Kuo, Ou, Chen
• Primary Examiner(s): Tran; Minhloan
• Assistant Examiner(s): Liu; Benjamin Tzu-Hung
• Application Number:
  US10/906,458
• Publication Number:
  US 20050211995A1
• Time in Patent Office: 1,142 Days
• Field of Search: 257/95, 257/98, 257/103, 257/E33.005, 257/E33.006, 257/E33.033, 257/E33.068, 257/E33.074
• US Class Current: 257/95
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

A high-efficiency light-emitting element includes a substrate, a first nitride semiconductor layer formed on the substrate, a nitride light-emitting layer formed on the first nitride semiconductor layer, and a second nitride semiconductor layer formed on the nitride light-emitting layer including a plurality of hexagonal-pyramid cavities on the surface of the second nitride semiconductor layer opposite to the nitride light-emitting layer.

Claims

1. A high-efficiency light-emitting element comprising:

a substrate;

a first nitride semiconductor layer formed on and electrically isolated from the substrate;

a nitride light-emitting layer formed on the first nitride semiconductor layer;

a second nitride semiconductor layer formed on the nitride light-emitting layer comprising a p-type semiconductor layer; and

a plurality of hexagonal-pyramid cavities extending downward from at least one of surfaces on the first nitride semiconductor layer and the second nitride semiconductor layer.

2. The high-efficiency light-emitting element of claim 1 wherein the top diagonal length of the hexagonal-pyramid cavity is between 10 nm and 1 um.

3. The high-efficiency light-emitting element of claim 1 wherein the density of the plurality of hexagonal-pyramid cavities is between 5*10⁷ cm⁻

2 and 1*10¹⁰ cm<sup>−

2</sup>.

4. The high-efficiency light-emitting element of claim 1 wherein the depth of the hexagonal-pyramid cavity is between 10 nm and 1 μ

m.

5. The high-efficiency light-emitting element of claim 1 further comprising a buffer layer between the substrate and the first nitride semiconductor layer.

6. The high-efficiency light-emitting element of claim 5 wherein the buffer layer comprises at least one material selected from a material group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.

7. The high-efficiency light-emitting element of claim 1 further comprising a transparent conductive layer formed on the second nitride semiconductor layer.

8. The high-efficiency light-emitting element of claim 7 further comprising an invert tunneling contact layer between the second nitride semiconductor layer and the transparent conductive layer, wherein the conductivity type of the invert tunneling contact layer is opposite to the conductivity type of the second nitride semiconductor layer and carrier concentration of the invert tunneling contact layer is no less than 5*10¹⁸ cm⁻

3.

9. The high-efficiency light-emitting element of claim 8 wherein the invert tunneling contact layer comprises at least one material selected from a material group consisting of InGaN and GaN.

10. The high-efficiency light-emitting element of claim 7 further comprising a low-resistivity tunneling contact layer between the second nitride semiconductor layer and the transparent conductive layer, wherein the low-resistivity tunneling contact layer is a superlattice structure.

11. The high-efficiency light-emitting element of claim 10 wherein the superlattice structure comprises at least one material selected from a material group consisting of Al_XGa_1-XN and In_yGa_1-yN, wherein 0≦

x≦

1, 0≦

y≦

1 and x and y can not be 0 at the same time.

12. The high-efficiency light-emitting element of claim 7 wherein the transparent conductive layer is a thin metallic conductive layer.

13. The high-efficiency light-emitting element of claim 12 wherein the thin metallic conductive layer comprises at least one material selected from a material group consisting of Al, Ti, Ti/Al, Cr/Al, Ti/Au, Cr/Au, Ni/Au, TiW, TiN, WSi, Au/Ge, Pt, Pd and Rb.

14. The high-efficiency light-emitting element of claim 7 wherein the transparent conductive layer is a transparent oxide conductive layer.

15. The high-efficiency light-emitting element of claim 14 wherein the transparent oxide conductive layer comprises at least one material selected from a material group consisting of indium tin oxide, cadmium tin oxide, antimony tin oxide, zinc aluminum oxide, and zinc tin oxide.

16. The high-efficiency light-emitting element of claim 7 wherein the transparency of the transparent conductive layer is above 50% when the wavelength range is between 300 nm and 700 nm.

17. The high-efficiency light-emitting element of claim 1 wherein the substrate is a sapphire substrate.

18. The high-efficiency light-emitting element of claim 17 wherein the sapphire substrate is a (0001) or (11-20) directional substrate and comprises an off angle between 0°

and 10°

.

19. The high-efficiency light-emitting element of claim 1 wherein the substrate comprises at least one material selected from a material group consisting of sapphire, GaN, AlN, SiC, ZnO, MgO, MgAl₂ O₄, and glass.

20. The high-efficiency light-emitting element of claim 1 wherein the first nitride semiconductor layer comprises at least one material selected from a material group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.

21. The high-efficiency light-emitting element of claim 1 wherein the first nitride semiconductor layer comprises at least one n-type nitride semiconductor layer, and the second nitride semiconductor layer comprises at least one p-type nitride semiconductor layer.

22. The high-efficiency light-emitting element of claim 1 wherein the first nitride semiconductor layer comprises at least one p-type nitride semiconductor layer, and the second nitride semiconductor layer comprises at least one n-type nitride semiconductor layer.

23. The high-efficiency light-emitting element of claim 1 wherein the nitride light-emitting layer comprises at least one material selected from a material group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.

24. The high-efficiency light-emitting element of claim 1 wherein the nitride light-emitting layer is in a double-heterostructure, a single-quantum well structure, or a multiple-quantum well structure.

25. The high-efficiency light-emitting element of claim 1 wherein the second nitride semiconductor layer comprises at least one material selected from a material group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.

26. The high-efficiency light-emitting element of claim 1 wherein the plurality of hexagonal-pyramid cavities on the surface of the second nitride semiconductor layer are formed by an epitaxial growth method.

27. The high-efficiency light-emitting element of claim 1 wherein the plurality of hexagonal-pyramid cavities on the surface of the second nitride semiconductor layer are formed by a wet etching method.

28. The high-efficiency light-emitting element of claim 1 wherein the plurality of hexagonal-pyramid cavities on the surface of the second nitride semiconductor layer are formed by an epitaxial growth method and a wet etching method.

29. The high-efficiency light-emitting element of claim 1 wherein the distance between the bottom of the hexagonal-pyramid cavities and the top surface of the first nitride semiconductor layer is no less than the distance between the top surface of the nitride light-emitting layer and the top surface of the first nitride semiconductor layer.

30. The high-efficiency light-emitting element of claim 1 wherein the first nitride semiconductor layer comprises a first surface and a second surface distant from the substrate, and the nitride light-emitting layer is formed on the first surface.

31. The high-efficiency light-emitting element of claim 30 wherein a plurality of hexagonal-pyramid cavities are formed on the second surface of the first nitride semiconductor layer.

32. The high-efficiency light-emitting element of claim 31 wherein a first electrode is formed on the second surface of the first nitride semiconductor layer with the hexagonal-pyramid cavity.

33. The high-efficiency light-emitting element of claim 31 wherein a first electrode is formed on the second surface of the first nitride semiconductor layer without the hexagonal-pyramid cavity.

34. The high-efficiency light-emitting element of claim 31 wherein the diagonal length of the hexagonal-pyramid cavity on the second surface of the first nitride semiconductor layer is between 10 nm and 1 μ

m.

35. The high-efficiency light-emitting element of claim 31 wherein the density of the plurality of hexagonal-pyramid cavities on the second surface of the first nitride semiconductor layer is between 1*10⁷ cm⁻

2 and 1*10¹¹ cm<sup>−

2</sup>.

36. The high-efficiency light-emitting element of claim 31 wherein the depth of the hexagonal-pyramid cavity on the second surface of the first nitride semiconductor layer is between 10 nm and 1 μ

m.

37. The high-efficiency light-emitting element of claim 31 wherein the hexagonal-pyramid cavities on the second surface of the first nitride semiconductor layer are formed by a wet etching method.

38. The high-efficiency light-emitting element of claim 1 wherein the substrate is a C-(0001) sapphire substrate, an angle between each adjacent pyramid surface inside the hexagonal-pyramid cavity is 120 degrees substantially, the pyramid surfaces includes a (10-11) or (11-22) lattice surface, and an angle between the pyramid surface and the central normal of the hexagonal-pyramid cavity is 60 degrees substantially.

39. A high-efficiency light-emitting element comprising:

a substrate;

a first nitride semiconductor layer formed on and electrically isolated from the substrate comprising;

a first surface distant from the substrate; and

a second surface distant from the substrate and comprising a plurality of hexagonal-pyramid cavities, wherein the hexagonal-pyramid cavity extends downward from the second surface of the first nitride semiconductor layer;

a nitride light-emitting layer formed on the first surface; and

a second nitride semiconductor layer formed on the nitride light-emitting layer.

40. The high-efficiency light-emitting element of claim 39 wherein the top diagonal length of the hexagonal-pyramid cavity is between 10 nm and 1 μ

m.

41. The high-efficiency light-emitting element of claim 39 wherein the density of the plurality of hexagonal-pyramid cavities is between 5*10⁷ cm⁻

2 and 1*10¹⁰ cm<sup>−

2</sup>.

42. The high-efficiency light-emitting element of claim 39 wherein the depth of the hexagonal-pyramid cavity is between 10 nm and 1 μ

m.

43. The high-efficiency light-emitting element of claim 39 further comprising a transparent conductive layer formed on the second nitride semiconductor layer.

44. The high-efficiency light-emitting element of claim 43 further comprising an invert tunneling contact layer between the second nitride semiconductor layer and the transparent conductive layer, wherein the conductivity type of the invert tunneling contact layer is opposite to the conductivity type of the second nitride semiconductor layer and carrier concentration of the invert tunneling contact layer is not less than 5*10¹⁸ cm⁻

3.

45. The high-efficiency light-emitting element of claim 43 further comprising a low-resistivity tunneling contact layer between the second nitride semiconductor layer and the transparent conductive layer, wherein the low-resistivity tunneling contact layer is in a superlattice structure.

46. The high-efficiency light-emitting element of claim 43 wherein the transparent conductive layer is a thin metallic conductive layer.

47. The high-efficiency light-emitting element of claim 43 wherein the transparent conductive layer is a transparent oxide conductive layer.

48. The high-efficiency light-emitting element of claim 43 wherein the transparancy of the transparent conductive layer is above 50% when the wavelength range is between 300 nm and 700 nm.

49. The high-efficiency light-emitting element of claim 39 wherein the substrate is a sapphire substrate.

50. The high-efficiency light-emitting element of claim 49 wherein the sapphire substrate is a (0001) or (11-20) orientation substrate and comprises an off angle between 0°

and 10°

.

51. The high-efficiency light-emitting element of claim 39 wherein the plurality of hexagonal-pyramid cavities are formed by a wet etching method.