Light-emitting device

• US 7,385,226 B2
• Filed: 06/21/2005
• Issued: 06/10/2008
• Est. Priority Date: 03/24/2004
• Status: Active Grant

• Current Assignee: Epistar Corporation
• Original Assignee: Epistar Corporation
• Inventors: Lai, Shih-Kuo, Ou, Chen, Lin, Ting-Yang
• Primary Examiner(s): Tran; Minhloan
• Assistant Examiner(s): LIU, BENJAMIN T
• Application Number:
  US11/160,354
• Publication Number:
  US 20050285136A1
• Time in Patent Office: 1,085 Days
• Field of Search: 257/91, 257/95, 257/99, 257/103, 257/E33.064, 257/E33.065, 257/98, 257/745, 257/E33.033, 257/E33.034, 257/E33.043, 257/E33.074
• US Class Current: 257/95
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers

Abstract

A light-emitting device includes a substrate, a first nitride semiconductor stack formed on the substrate, a nitride light-emitting layer formed on the first nitride semiconductor stack, a second nitride semiconductor stack formed on the nitride light-emitting layer, and a first transparent conductive oxide layer formed on the second nitride semiconductor stack. The second nitride semiconductor stack includes a plurality of hexagonal-pyramid cavities formed in an upper surface of the second nitride semiconductor stack. The plurality of hexagonal-pyramid cavities of the second nitride semiconductor stack are filled with the first transparent conductive oxide layer, and a low-resistance ohmic contact is generated at the inner surfaces of the plurality of hexagonal-pyramid cavities so as to decrease the operation voltage and improve light-emitting efficiency of the light-emitting device.

Claims

1. A light-emitting device comprising:

a substrate;

a first nitride semiconductor stack formed on the substrate;

a nitride light-emitting layer formed on the first nitride semiconductor stack in parallel to a surface of the substrate;

a second nitride semiconductor stack formed on the nitride light-emitting layer, comprising at least one p-type nitride semiconductor layer and a plurality of hexagonal-pyramid cavities extending downward from a surface of the second nitride semiconductor stack opposite to the nitride light-emitting layer; and

a first transparent conductive oxide layer formed on the plurality of hexagonal-pyramid cavities in a low-resistance ohmic contact.

2. The light-emitting device of claim 1 wherein a diagonal length, in the surface of the second nitride semiconductor stack, of one of the hexagonal-pyramid cavities is within the range of 10 nm to 1 μ

m.

3. The light-emitting device of claim 1, wherein the density of the hexagonal-pyramid cavities is within the range of 1×

10⁷ cm<sup>−

2</sup> to 1×

10¹¹ cm<sup>−

2</sup>.

4. The light-emitting device of claim 1, wherein a depth of one of the hexagonal-pyramid cavities is within the range of 10 nm to 1 μ

m.

5. The light-emitting device of claim 1 further comprising a buffer layer formed between the substrate and the first nitride semiconductor stack.

6. The light-emitting device of claim 1, wherein the first transparent conductive oxide layer comprises at least one material selected from a group consisting of indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide.

7. The light-emitting device of claim 1, wherein a transmittance of the first transparent conductive oxide layer is more than 50% when a wavelength of light is within the range of 300 nm to 700 nm.

8. The light-emitting device of claim 1, wherein a thickness of the first transparent conductive oxide layer is within the range of 50 nm to 1 μ

m.

9. The light-emitting device of claim 1, wherein the substrate is a C-(0001) sapphire substrate, an angle between every two adjacent pyramid surfaces of each of the hexagonal-pyramid cavities is substantially 120 degrees, and each of the pyramid surfaces includes a (10-11) or (11-22) lattice surface group.

10. The light-emitting device of claim 1, wherein the substrate is a (0001) or (11-20) sapphire substrate having an off angle from 0 to 10 degrees.

11. The light-emitting device of claim 1, wherein the substrate comprises at least one material selected from a group consisting of GaN, AlN, SiC, GaAs, GaP, Si, ZnO, MgO, MgAl₂O₄, and glass.

12. The light-emitting device of claim 1, wherein the first nitride semiconductor stack comprises at least one material selected from a group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.

13. The light-emitting device of claim 1, wherein the first nitride semiconductor stack comprises at least one n-type nitride semiconductor layer.

14. The light-emitting device of claim 1, wherein the first nitride semiconductor stack comprises at least one p-type nitride semiconductor layer.

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

16. The light-emitting device of claim 1, wherein the nitride light-emitting layer includes a double hetero-structure, a single quantum-well structure, or a multiple quantum-well structure.

17. The light-emitting device of claim 1, wherein the second nitride semiconductor stack comprises at least one material selected from a group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.

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

19. The light-emitting device of claim 1, wherein the hexagonal-pyramid cavities of the second nitride semiconductor stack are formed by epitaxial growth.

20. The light-emitting device of claim 1, wherein the hexagonal-pyramid cavities of the second nitride semiconductor stack are formed by performing a wet etching process.

21. The light-emitting device of claim 1, wherein the hexagonal-pyramid cavities of the second nitride semiconductor stack are formed by epitaxial growth and performing a wet etching process.

22. The light-emitting device of claim 1, wherein the distance from the bottom of the hexagonal-pyramid cavity to the substrate is not less than the distance from the upper surface of the nitride light-emitting layer to the substrate.

23. The light-emitting device of claim 1, wherein the contact resistance formed at inner surfaces of the hexagonal-pyramid cavities contacting with the first transparent conductive oxide layer is lower than the contact resistance formed at the surface of the second nitride semiconductor stack contacting with the first transparent conductive oxide layer.

24. The light-emitting device of claim 1, wherein the refractive index of the first transparent conductive oxide layer is between the refractive indexes of nitride material and package material.

25. The light-emitting device of claim 1, wherein the surface of the first nitride semiconductor stack far from the substrate includes a first surface and a second surface, the nitride light-emitting layer being formed on the first surface of the first nitride semiconductor stack.

26. The light-emitting device of claim 25 further comprising a second transparent conductive oxide layer formed on the second surface of the first nitride semiconductor stack.

27. The light-emitting device of claim 26, wherein the second transparent conductive oxide layer comprises at least one material selected from a group consisting of indium tin oxide, cadmium tin oxide, antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide.

28. The light-emitting device of claim 26, wherein the refractive index of the second transparent conductive oxide layer is between the refractive indexes of nitride material and package material.

29. The light-emitting device of claim 25 wherein the second surface of the first nitride semiconductor stack is a high light extraction efficiency surface.

30. The light-emitting device of claim 29 wherein the high light extraction efficiency surface is formed with a hexagonal-pyramid cavity formed in the high light extraction efficiency surface.

31. The light-emitting device of claim 30, wherein a second transparent conductive oxide layer is formed on the second surface of the first nitride semiconductor stack that is formed with the hexagonal-pyramid cavities.

32. The light-emitting device of claim 31, wherein each of the hexagonal-pyramid cavities of the first nitride semiconductor stack is substantially filled with the second transparent conductive oxide layer.

33. The light-emitting device of claim 30, wherein a diagonal length, in the surface of the second nitride semiconductor stack, of one of the hexagonal-pyramid cavities is within the range of 10 nm to 1 μ

m.

34. The light-emitting device of claim 30, wherein a density of the hexagonal-pyramid cavities is within the range of 1×

10⁷ cm<sup>−

2</sup> to 1×

10¹¹ cm<sup>−

2</sup>.

35. The light-emitting device of claim 30, wherein a depth of the hexagonal-pyramid cavity is within the range of 10 nm to 1 μ

m.

36. The light-emitting device of claim 30, wherein the hexagonal-pyramid cavities are formed by performing a wet etching process.

37. The light-emitting device of claim 31, wherein the second transparent conductive oxide layer comprises at least one material selected from a group consisting of indium tin oxide, cadmium tin oxide, antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide.

38. The light-emitting device of claim 29, wherein the high light extraction efficiency surface is formed with a rough structure.

39. The light-emitting device of claim 38, wherein a second transparent conductive oxide layer is formed on the second surface of the first nitride semiconductor stack that is formed with the rough structure.

40. The light-emitting device of claim 39, wherein the second transparent conductive oxide layer comprises at least one material selected from a group consisting of indium tin oxide, cadmium tin oxide, antimony tin oxide, indium zinc oxide, zinc aluminum oxide, and zinc tin oxide.

41. The light-emitting device of claim 38, wherein the rough structure is formed by performing a wet etching process.

42. The light-emitting device of claim 31, wherein the refractive index of the second transparent conductive oxide layer is between the refractive indexes of nitride material and package material.