Nitride-based semiconductor light-emitting device

1. A nitride-based semiconductor light-emitting device comprising:

a first conductivity type first nitride-based semiconductor layer formed on a substrate;

an active layer, formed on said first nitride-based semiconductor layer;

a first undoped optical guide layer formed on said active layer;

a second conductivity type second nitride-based semiconductor layer, having a single layer structure with a thickness of at least 0.1 μm, formed on said first undoped optical guide layer;

an undoped contact layer formed directly on said second nitride-based semiconductor layer; and

an electrode formed directly on said undoped contact layer, wherein

said undoped contact layer consists of a nitride-based semiconductor and has a single-layer structure and a thickness of at least about 1 nm and not more than about 10 nm, and the undoped contact layer does not include Al.

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

the band gap of said undoped contact layer is smaller than the band gap of said second nitride-based semiconductor layer.

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

said second conductivity type second nitride-based semiconductor layer includes a second conductivity type cladding layer consisting of AlGaN.

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

said first conductivity type first nitride-based semiconductor layer is an n-type first nitride-based semiconductor layer, and

said second conductivity type second nitride-based semiconductor layer is a p-type second nitride-based semiconductor layer.

5. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said undoped contact layer has a band gap larger than the band gap of said active layer.

6. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said undoped contact layer contains InGaN.

7. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said undoped contact layer contains GaN.

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

said undoped contact layer has a multilayer structure consisting of a plurality of undoped nitride-based semiconductor layers.

9. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

an optical guide layer is not formed between said active layer and said first conductivity type first nitride-based semiconductor layer.

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

said second conductivity type second nitride-based semiconductor layer includes a second conductivity type second nitride-based semiconductor layer consisting of AlGaN, and

said first undoped optical guide layer includes an undoped optical guide layer consisting of GaN.

11. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said second conductivity type second nitride-based semiconductor layer includes a second conductivity type cladding layer having a projecting portion,

said undoped contact layer is formed on the upper surface of said projecting portion of said second conductivity type cladding layer, and

said projecting portion of said second conductivity type cladding layer and said undoped contact layer constitute a ridge portion.

12. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said active layer includes an active layer consisting of a nitride-based semiconductor containing In,

said nitride-based semiconductor light-emitting device further comprising a protective layer of a nitride-based semiconductor layer formed on said active layer for preventing In contained in said active layer from desorption.

13. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said first conductivity type first nitride-based semiconductor layer includes a first conductivity type contact layer, and

said first conductivity type contact layer also has a function for serving as a first conductivity type cladding layer.

14. The nitride-based semiconductor light-emitting device according to claim 13 , wherein

said substrate includes an insulating substrate.

15. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said electrode provided on said undoped contact layer is interdigitally formed.

16. The nitride-based semiconductor light-emitting device according to claim 1 , further comprising an undoped fifth nitride-based semiconductor layer formed between said substrate and said first conductivity type first nitride-based semiconductor layer.

17. The nitride-based semiconductor light-emitting device according to claim 16 , wherein

said undoped fifth nitride-based semiconductor layer is constituted of a nitride-based semiconductor having a low dislocation density formed by selective lateral growth.

18. The nitride-based semiconductor light-emitting device according to claim 16 , further comprising a plurality of mask layers having overhangs formed on said substrate at prescribed intervals, wherein

said undoped fifth nitride-based semiconductor layer is formed by selective lateral growth to fill up clearances between said mask layers.

19. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

said substrate is a first conductivity type GaN substrate.

20. The nitride-based semiconductor light-emitting device according to claim 1 , wherein

a second undoped optical guide layer is formed between the first nitride-based semiconductor layer and said active layer.

21. The nitride-based semiconductor light-emitting device according to claim 20 , wherein

said second undoped optical guide layer has a thickness smaller than the thickness of said first undoped optical guide layer.

22. A nitride-based semiconductor light-emitting device comprising:

a first conductivity type first nitride-based semiconductor layer formed on a substrate;

an active layer, formed on said first nitride-based semiconductor layer;

a second conductivity type second nitride-based semiconductor layer, having a single layer structure with a thickness of at least 0.1 μm, formed on said active layer;

an undoped contact layer formed directly on said second nitride-based semiconductor layer; and

an electrode formed directly on said undoped contact layer, wherein

said undoped contact layer consists of a nitride-based semiconductor and has a thickness of at least about 1 nm and not more than about 10 nm.