Nitride-based semiconductor laser device and method of forming the same

• US 20020146855A1
• Filed: 01/30/2002
• Published: 10/10/2002
• Est. Priority Date: 02/02/2001
• Status: Active Grant

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Nomura, Yasuhiko, Oota, Kiyoshi, Yamaguchi, Tsutomu, Goto, Takenori
• Granted Patent: US 6,743,702 B2
• Time in Patent Office: Days
• US Class Current: 438/29
• CPC Class Codes: H01L 21/28575 on semiconductor bodies comprising AIIIBV compounds
• CPC Class Codes: H01S 5/0234 Up-side down mountings, e.g. Flip-chip, epi-side down mountings or junction down mountings
• CPC Class Codes: H01S 5/04252 characterised by the material
• CPC Class Codes: H01S 5/04254 characterised by the shape
• CPC Class Codes: H01S 5/04257 having positive and negative electrodes on the same side of the substrate
• CPC Class Codes: H01S 5/22 having a ridge or stripe structure
• CPC Class Codes: H01S 5/3201 incorporating bulkstrain effects, e.g. strain compensation, strain related to polarisation
• CPC Class Codes: H01S 5/32341 blue laser based on GaN or GaP

Abstract

A highly reliable semiconductor laser device having a low operating voltage is obtained by increasing adhesive force of the overall electrode layer to a nitride-based semiconductor layer without deteriorating a low contact property. This nitride-based semiconductor laser device comprises a nitride-based semiconductor layer formed on an active layer and an electrode layer formed on the nitride-based semiconductor layer, while the electrode layer includes a first electrode layer containing a material having strong adhesive force to the nitride-based semiconductor layer and a second electrode layer, formed on the first electrode layer, having weaker adhesive force to the nitride-based semiconductor layer than the first electrode layer for reducing contact resistance of the electrode layer with respect to the nitride-based semiconductor layer. Thus, the adhesive force of the overall electrode layer to the nitride-based semiconductor layer is increased due to the first electrode layer, and lower contact resistance is attained due to the second electrode layer. Therefore, the device can be improved in reliability and reduced in operating voltage.

Claims

1. A nitride-based semiconductor laser device comprising:

a nitride-based semiconductor layer formed on an active layer; and

an electrode layer formed on said nitride-based semiconductor layer, wherein

said electrode layer includes;

a first electrode layer containing a material having strong adhesive force to said nitride-based semiconductor layer, and

a second electrode layer, formed on said first electrode layer, having weaker adhesive force to said nitride-based semiconductor layer than said first electrode layer for reducing contact resistance of said electrode layer with respect to said nitride-based semiconductor layer.

2. The nitride-based semiconductor laser device according to claim 1, wherein

said second electrode layer has lower contact resistance with respect to said nitride-based semiconductor layer than said first electrode layer.

3. The nitride-based semiconductor laser device according to claim 1, wherein

said first electrode layer has a thickness of not more than 3 nm.

4. The nitride-based semiconductor laser device according to claim 1, wherein

said first electrode layer contains at least one material selected from a group consisting of Pt, Ni, Cr, Ti, Hf and Zr, and

said second electrode layer contains Pd.

5. The nitride-based semiconductor laser device according to claim 4, wherein

said first electrode layer includes a Pt layer, and

said second electrode layer includes a multilayer film having a Pd layer.

6. The nitride-based semiconductor laser device according to claim 5, wherein

the uppermost layer of said second electrode layer includes a metal layer serving as an etching mask.

7. The nitride-based semiconductor laser device according to claim 4, further comprising a mixed layer, formed between said first and second electrode layers, including a Pt layer and a Pd layer.

8. The nitride-based semiconductor laser device according to claim 1, wherein

said nitride-based semiconductor layer has an irregular surface.

9. The nitride-based semiconductor laser device according to claim 8, wherein

said nitride-based semiconductor layer having said irregular surface has an In composition of at least 3% and a thickness of not more than 20 nm.

10. The nitride-based semiconductor laser device according to claim 1, wherein

said nitride-based semiconductor layer includes a contact layer formed on a convex portion of a cladding layer, and

said convex portion of said cladding layer and said contact layer form a ridge portion.

11. The nitride-based semiconductor laser device according to claim 1, further comprising a base for mounting an element including said nitride-based semiconductor layer, said first electrode layer and said second electrode layer from the side of said active layer.

14. The method of forming a nitride-based semiconductor laser device according to claim 13, wherein

said second electrode layer has lower contact resistance with respect to said nitride-based semiconductor layer than said first electrode layer.

15. The method of forming a nitride-based semiconductor laser device according to claim 13, wherein

said first electrode layer has a thickness of not more than 3 nm.

16. The method of forming a nitride-based semiconductor laser device according to claim 13, wherein

said step of forming said first electrode layer on the surface of said nitride-based semiconductor layer includes a step of forming said first electrode layer and said second electrode layer on the surface of said nitride-based semiconductor layer and thereafter feeding a current between said second electrode layer and said nitride-based semiconductor layer thereby partially moving material included in said second electrode layer to a portion close to the surface of said nitride-based semiconductor layer.

17. The method of forming a semiconductor laser device according to claim 13, wherein

said step of forming said first electrode layer includes a step of forming said first electrode layer by any of electron beam heating evaporation, resistance heating evaporation and sputtering evaporation.

18. The method of forming a nitride-based semiconductor laser device according to claim 13, wherein

said nitride-based semiconductor layer includes a contact layer formed on a cladding layer, and

said step of forming said second electrode layer includes a step of forming said second electrode layer on a prescribed region of the upper surface of said first electrode layer by a lift off method,

said method further comprising a step of forming a ridge portion by partially etching said first electrode layer, said contact layer and said cladding layer through said second electrode layer serving as a mask after forming said second electrode layer.

19. The method of forming a nitride-based semiconductor laser device according to claim 13, wherein

said first electrode layer contains at least one material selected from a group consisting of Pt, Ni, Cr, Ti, Hf and Zr, and

said second electrode layer contains Pd.

20. The method of forming a nitride-based semiconductor laser device according to claim 13, wherein

said step of forming said nitride-based semiconductor layer includes a step of forming said nitride-based semiconductor layer having an irregular surface.

21. The method of forming a nitride-based semiconductor laser device according to claim 20, wherein

said nitride-based semiconductor layer having said irregular surface has an In composition of at least 3% and a thickness of not more than 20 nm.

12. A nitride-based semiconductor laser device comprising:

a nitride-based semiconductor layer formed on an active layer; and

an electrode layer formed on said nitride-based semiconductor layer, wherein

said electrode layer includes;

a first electrode layer containing a material having strong adhesive force to said nitride-based semiconductor layer, and

a second electrode layer, formed on said first electrode layer, having weaker adhesive force to said nitride-based semiconductor layer than said first electrode layer for reducing an energy barrier of said electrode layer against said nitride-based semiconductor layer.

13. A method of forming a nitride-based semiconductor laser device comprising steps of:

forming a nitride-based semiconductor layer on an active layer; and

forming an electrode layer on the surface of said nitride-based semiconductor layer, wherein

said step of forming said electrode layer includes steps of;

forming a first electrode layer containing a material having strong adhesive force to said nitride-based semiconductor layer, and

forming a second electrode layer having weaker adhesive force to said nitride-based semiconductor layer than said first electrode layer for reducing contact resistance of said electrode layer with respect to said nitride-based semiconductor layer on said first electrode layer.

22. A nitride-based semiconductor laser apparatus comprising:

a nitride-based semiconductor layer having an active layer and a ridge potion formed on said active layer; and

a first electrode layer, formed to come into contact with an exposed upper surface of said ridge portion, having a thickness larger than the distance between the lower surface of a cladding layer located under said active layer and the upper surface of said ridge portion.

23. The nitride-based semiconductor laser apparatus according to claim 22, wherein

said first electrode layer includes:

a first metal layer coming into contact with said ridge portion, and

a second metal layer formed on said first metal layer so that its surface is exposed, and

said second metal layer has a larger thickness than said first metal layer.

24. The nitride-based semiconductor laser apparatus according to claim 23, wherein

said second metal layer includes a p-side pad electrode consisting of Au.

25. The nitride-based semiconductor laser apparatus according to claim 23, further comprising a current blocking layer formed to cover regions excluding the upper surface of said ridge portion, wherein

said first metal layer is formed not only on said ridge portion but also on said current blocking layer.

26. The nitride-based semiconductor laser apparatus according to claim 25, further comprising a contact layer, consisting of a nitride-based semiconductor, formed on said ridge portion and said current blocking layer, wherein

said first metal layer is formed on said ridge portion and said current blocking layer through said contact layer.

27. The nitride-based semiconductor laser apparatus according to claim 23, wherein

said first metal layer includes a multilayer film consisting of different metals.

28. The nitride-based semiconductor laser apparatus according to claim 22, wherein

said first electrode layer includes:

a first metal layer coming into contact with said ridge portion, and

a second metal layer formed on said first metal layer so that its surface is exposed, and

said first metal layer has a larger thickness than said second metal layer.

29. The nitride-based semiconductor laser apparatus according to claim 28, wherein

said first metal layer includes a p-side electrode having an Au film larger in thickness than said second metal layer.

30. The nitride-based semiconductor laser apparatus according to claim 28, wherein

said first metal film includes a multilayer film consisting of different metals.

31. The nitride-based semiconductor laser apparatus according to claim 28, wherein

said first metal layer having a larger thickness than said second metal layer is formed to project only on the upper surface of said ridge portion.

32. The nitride-based semiconductor laser apparatus according to claim 22, wherein

said first electrode layer includes:

a first metal layer coming into contact with said ridge portion,

a second metal layer formed on said first metal layer, and

a third metal layer formed on said second metal layer, and

said third metal layer has a larger thickness than said first metal layer and said second metal layer.

33. The nitride-based semiconductor laser apparatus according to claim 32, wherein

said third metal layer includes a p-side thick-film electrode having an Au film larger in thickness than said first metal layer and said second metal layer.

34. The nitride-based semiconductor laser apparatus according to claim 32, wherein

each of said first metal layer, said second metal layer and said third metal layer has a multilayer structure.

35. The nitride-based semiconductor laser apparatus according to claim 22, further comprising a current blocking layer formed to cover regions excluding the upper surface of said ridge portion, wherein

said current blocking layer includes either a nitride-based semiconductor having a conductivity type different from that of said ridge portion or an insulator film.

36. The nitride-based semiconductor laser apparatus according to claim 35, wherein

said current blocking layer includes a current blocking layer consisting of an SiO₂ film.

37. The nitride-based semiconductor laser apparatus according to claim 35, wherein

said current blocking layer includes a current blocking layer consisting of any material of AlGaN, InGaN and GaN having a conductivity type different from that of said ridge portion.

38. The nitride-based semiconductor laser apparatus according to claim 35, wherein

said current blocking layer consists of a nitride-based semiconductor having a conductivity type different from that of said ridge portion,

said nitride-based semiconductor laser apparatus further comprising:

a second electrode layer formed on a surface exposed by partially removing said nitride-based semiconductor layer, and

a protective film consisting of an insulator film formed on a side surface exposed by partially removing said nitride-based semiconductor layer.

39. The nitride-based semiconductor laser apparatus according to claim 38, wherein

said current blocking layer includes a current blocking layer consisting of AlGaN, and

said protective film includes a protective film consisting of SiO₂.

40. The nitride-based semiconductor laser apparatus according to claim 22, further comprising a base for mounting an element including said nitride-based semiconductor layer and said first electrode layer from the side of said active layer.

41. The nitride-based semiconductor laser apparatus according to claim 40, wherein

said base includes a submount.

42. A nitride-based semiconductor laser apparatus comprising:

a nitride-based semiconductor layer having an active layer and a ridge portion formed on said active layer; and

a first electrode layer, formed to come into contact with an exposed upper surface of said ridge portion, having a thickness of at least 2 μ

m.