Semiconductor light emitting device

1. A semiconductor light emitting device comprising:

an n-type semiconductor layer;

an active layer formed on a first region of the n-type semiconductor layer, and emitting light;

a p-type semiconductor layer formed on the active layer;

a p-electrode formed on the p-type semiconductor layer, and including a first conductive oxide layer having an oxygen content lower than 40 atomic % and a second conductive oxide layer formed on the first conductive oxide layer and having a higher oxygen content than the oxygen content of the first conductive oxide layer, crystal grains in the first conductive oxide layer being smaller than crystal grains in the second conductive oxide layer; and

an n-electrode formed on a second region of the n-type semiconductor layer.

2. The device according to claim 1 , wherein the first conductive oxide layer contains at least one element selected from the group consisting of In, Zn, Sn, Ni, Mg, Cu, Au, Pd, Rh, and Ga.

3. The device according to claim 1 , wherein the first conductive oxide layer has a contact resistance lower than 1×10-2 Ω·cm.

4. The device according to claim 1 , wherein the first conductive oxide layer has a film thickness that is not smaller than 10 nm and not greater than 100 nm.

5. The device according to claim 1 , wherein the second conductive oxide layer has a higher transmittance than a transmittance of the first conductive oxide layer.

6. The device according to claim 1 , further comprising a substrate on which the n-type semiconductor layer is formed, wherein the substrate is one of a sapphire substrate and a semiconductor substrate.

7. A semiconductor light emitting device comprising:

a substrate;

an n-type semiconductor layer formed on the substrate;

an active layer formed on the n-type semiconductor layer, and emitting light;

a p-type semiconductor layer formed on the active layer;

a p-electrode formed on the p-type semiconductor layer, and including a first conductive oxide layer having an oxygen content lower than 40 atomic % and a second conductive oxide layer formed on the first conductive oxide layer and having a higher oxygen content than the oxygen content of the first conductive oxide layer, crystal grains in the first conductive oxide layer being smaller than crystal grains in the second conductive oxide layer; and

an n-electrode formed on the opposite surface of the substrate from the n-type semiconductor layer.

8. The device according to claim 7 , wherein the first conductive oxide layer contains at least one element selected from the group consisting of In, Zn, Sn, Ni, Mg, Cu, Au, Pd, Rh, and Ga.

9. The device according to claim 7 , wherein the first conductive oxide layer has a contact resistance lower than 1×10-2 Ω·cm.

10. The device according to claim 7 , wherein the first conductive oxide layer has a film thickness that is not smaller than 10 nm and not greater than 100 nm.

11. The device according to claim 7 , wherein the second conductive oxide layer has a higher transmittance than a transmittance of the first conductive oxide layer.

12. The device according to claim 7 , wherein the substrate is a semiconductor substrate.

13. The device according to claim 1 , wherein the first conductive oxide layer has a film thickness that is not smaller than 30 nm.

14. The device according to claim 1 , wherein the first conductive oxide layer has a film thickness that is not smaller than 30 nm and not greater than 50 nm.

15. The device according to claim 7 , wherein the first conductive oxide layer has a film thickness that is not smaller than 30 nm.

16. The device according to claim 7 , wherein the first conductive oxide layer has a film thickness that is not smaller than 30 nm and not greater than 50 nm.

17. The device according to claim 1 , wherein the second conductive oxide layer has an oxygen content more than 61 atomic %.

18. The device according to claim 7 , wherein the second conductive oxide layer has an oxygen content more than 61 atomic %.