Semiconductor light emitting device having a silver p-contact

• US 20010015442A1
• Filed: 01/16/2001
• Published: 08/23/2001
• Est. Priority Date: 12/15/1997
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Watanabe, Satoshi, Kondoh, You, Nakagawa, Shigeru, Kaneko, Yawara, Yamada, Norihide
• Granted Patent: US 6,900,472 B2
• Time in Patent Office: Days
• US Class Current: 257/79
• CPC Class Codes: H01L 2224/4847 the connecting portion on the bonding area of the semiconductor or solid-state body being a wedge bond
• CPC Class Codes: H01L 33/40 Materials therefor
• CPC Class Codes: H01L 33/42 Transparent materials

Abstract

A light emitting device is constructed on a substrate. The device includes an n-type semiconductor layer in contact with the substrate, an active layer for generating light, the active layer being in electrical contact with the n-type semiconductor layer. A p-type semiconductor layer is in electrical contact with the active layer, and a p-electrode is in electrical contact with the p-type semiconductor layer. The p-electrode includes a layer of silver in contact with the p-type semiconductor layer. A bonding layer is formed overlying the silver layer to make an electrical connection to the silver layer. The silver layer may be thin and transparent or thicker (greater than 20 nm) and reflective.

Claims

1. A light emitting device comprising:

a substrate;

an n-type semiconductor layer;

an active layer for generating light, said active layer being in electrical contact with said n-type semiconducting layer;

a p-type semiconductor layer in electrical contact with said active layer; and

a p-electrode in electrical contact with said p-type semiconductor layer, said p-electrode comprising at least a layer of silver having a thickness sufficient to reflect greater than 50% of light incident thereon, wherein a portion of said generated light exits said device through said substrate after being reflected from said p-electrode, and wherein said p-electrode further comprises a bonding layer in electrical contact with said layer of silver for making electrical connections to said layer of silver.

2. The light emitting device of

claim 1

wherein said n-type semiconductor layer and said p-type semiconductor layer comprise group III nitride semiconducting materials.

3. The light emitting device of

claim 1

wherein said silver layer is greater than or equal to 20 nm in thickness.

4. The light emitting device of

claim 1

wherein said p-electrode further comprises a fixation layer overlying and in electrical contact with said layer of silver.

5. The light emitting device of

claim 4

wherein said fixation layer comprises a metal.

6. The light emitting device of

claim 5

wherein said fixation layer comprises a metal chosen from the group consisting of nickel, palladium, and platinum.

7. The light emitting device of

claim 1

wherein said p-electrode further comprises a dielectric fixation layer overlying said layer of silver.

8. The light emitting device of

claim 7

wherein said fixation layer comprises a compound chosen from the group consisting of TiO₂ and Al₂O₃.

9. The light emitting device of

claim 1

wherein said bonding layer comprises a metal chosen from the group consisting of gold, nickel, aluminum, and indium.

10. The light emitting device of

claim 1

wherein said bonding layer covers less than half of said layer of silver.

11. The light emitting device of

claim 1

wherein said bonding layer is a multi-layered structure.

12. The light emitting device of

claim 1

wherein said p-electrode further comprises a diffusion barrier layer between said bonding layer and said layer of silver, said diffusion barrier layer providing an electrical path between said bonding layer and said layer of silver, said diffusion barrier layer for preventing constituents from said bonding layer from interdiffusing with said layer of silver.

13. The light emitting device of

claim 12

wherein said diffusion barrier layer comprises a metal.

14. The light emitting device of

claim 13

wherein said diffusion barrier layer comprises nickel.

15. The light emitting device of

claim 12

wherein said diffusion barrier layer encapsulates said layer of silver.

16. The light emitting device of

claim 12

wherein said diffusion barrier layer is a multi-layered structure.

17. The light emitting device of

claim 1

further comprising:

an n-electrode comprising a layer of electrically conducting material in electrical contact with said n-type semiconductor layer; and

a package having first and second conductors thereon electrically connected to said p-electrode and said n-electrode, respectively.

18. A method for fabricating a light emitting device comprising:

forming an n-type semiconductor layer;

forming an active layer in contact with said n-type semiconductor layer, said active layer generating light by the recombination of holes and electrons therein;

forming a p-type semiconductor layer in contact with a surface of said active layer opposite a surface contacting said n-type semiconductor layer;

forming at least a layer of silver on said p-type semiconductor layer; and

forming a bonding layer overlying said layer of silver for making electrical connections to said layer of silver.

19. The method of

claim 18

wherein said n-type and p-type semiconductor layers comprise group III nitride semiconducting materials.

20. The method of

claim 18

wherein said n-type semiconductor layer is formed on a substrate.

21. The method of

claim 18

further comprising forming a fixation layer overlying said layer of silver.

22. The method of

claim 21

wherein forming said bonding layer comprises depositing said bonding layer on said fixation layer.

23. The method of

claim 22

wherein said fixation layer comprises a dielectric.

24. The method of

claim 23

wherein said dielectric is chosen from the group consisting of TiO₂ and Al₂O₃.

25. The method of

claim 22

wherein said fixation layer comprises an electrically conducting layer.

26. The method of

claim 25

wherein said electrically conducting layer comprises a metal chosen from the group consisting of nickel, palladium, and platinum.

27. The method of

claim 18

wherein said bonding layer comprises a metal chosen from the group consisting of gold, nickel, aluminum, and indium.

28. The method of

claim 18

wherein said forming said bonding layer comprises forming said bonding layer to cover less than half of said layer of silver.

29. The method of

claim 18

wherein said forming said bonding layer comprises forming a multi-layered bonding layer structure.

30. The method of

claim 18

further comprising forming a diffusion barrier layer between said bonding layer and said layer of silver, said diffusion barrier layer providing an electrical path between said bonding layer and said layer of silver, said diffusion barrier layer for preventing constituents from said bonding layer from interdiffusing with said layer of silver.

31. The method of

claim 30

wherein said diffusion barrier layer comprises a metal.

32. The method of

claim 30

wherein said diffusion barrier layer comprises nickel.

33. The method of

claim 30

wherein said diffusion barrier layer is formed to encapsulate said layer of silver.

34. The method of

claim 30

wherein said forming said diffusion barrier layer comprises forming a multi-layered diffusion barrier layer.

35. The method of

claim 18

further comprising annealing said p-type semiconductor layer and said layer of silver by heating said light emitting device to a temperature greater than 200°

C.

36. A light emitting device comprising:

a substrate;

an n-type semiconductor layer;

an active layer for generating light, said active layer being in electrical contact with said n-type semiconducting layer;

a p-type semiconductor layer in electrical contact with said active layer; and

a p-electrode in electrical contact with said p-type semiconductor layer, said p-electrode comprising at least a substantially transparent layer of silver, and wherein said p-electrode further comprises a bonding layer in electrical contact with said layer of silver for making electrical connections to said layer of silver.