Nitride-based semiconductor light-emitting device

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

a first conductive type first nitride-based semiconductor layer formed on the surface of a conductive substrate;

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

a second conductive type second nitride-based semiconductor layer formed on said active layer and having a first carrier concentration; and

a light transmission layers through which light formed in the active layer is emitted from the device, formed on said second nitride-based semiconductor layer, the light transmission layer consisting of a nitride-based semiconductor layer having a second carrier concentration lower than the first carrier concentration of said second nitride-based semiconductor layer.

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

said first conductive type first nitride-based semiconductor layer is a p-type nitride-based semiconductor layer, and

said second conductive type second nitride-based semiconductor layer is an n-type nitride-based semiconductor layer.

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

said light transmission layer includes an undoped nitride-based semiconductor layer.

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

said light transmission layer includes a second conductive type nitride-based semiconductor layer doped with a second conductive type impurity.

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

said light transmission layer includes a nitride-based semiconductor layer containing at least Al.

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

said light transmission layer includes said nitride based semiconductor layer of AlGaN.

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

said light transmission layer has a textured surface.

8. The nitride-based semiconductor light-emitting device according to claim 1 , further comprising a layer, formed on said light transmission layer, having a textured surface and consisting of a material other than a nitride-based semiconductor.

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

said layer consisting of said material other than a nitride-based semiconductor includes an insulating film.

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

said light transmission layer consists of a material substantially identical to the material for said second nitride-based semiconductor layer.

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

said light transmission layer and said second nitride-based semiconductor layer are formed by GaN layers.

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

said light transmission layer and said second nitride-based semiconductor layer are formed by AlGaN layers.

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

said first nitride-based semiconductor layer is formed on the surface of said conductive substrate through a first electrode layer, and

said first electrode layer also functions as a reflecting film.

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

the surface of said first electrode layer closer to said first nitride-based semiconductor layer is textured.

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

said light transmission layer is formed on a partial region of said second nitride-based semiconductor layer,

the nitride-based semiconductor light-emitting device further comprising a second electrode layer formed to be in contact with a region of the surface of said second nitride-based semiconductor layer not formed with said light transmission layer.

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

said light transmission layer has an opening, and

said second electrode layer is formed in said opening to be in contact with the surface of said second nitride-based semiconductor layer.

17. The nitride-based semiconductor light-emitting device according to claim 15 , further comprising a layer, formed on said light transmission layer, consisting of a material other than a nitride-based semiconductor, wherein

said layer consisting of said material other than a nitride-based semiconductor and said light transmission layer have opening, and

said second electrode layer is formed in said openings to be in contact with the surface of said second nitride-based semiconductor layer.

18. The nitride-based semiconductor light-emitting device according to claim 1 , further comprising a protective film covering the side surfaces of said first nitride-based semiconductor layer, said active layer, said second nitride-based semiconductor layer and said light transmission layer.

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

said light transmission layer has a side surface inclined by a prescribed angle with respect to the normal of a light emission surface.

20. The nitride-based semiconductor light-emitting device according to claim 1 , further comprising an electrode on a portion of the second nitride-based semiconductor layer leaving an exposed portion of the second nitride-based semiconductor layer, wherein the light transmission layer is formed on the exposed portion of the second nitride-based semiconductor layer.