Light-emitting device

1. A light-emitting device, comprising:

a semiconductor stack comprising a first semiconductor layer, a second semiconductor layer, and an active layer formed between the first semiconductor layer and the second semiconductor layer, wherein the active layer is capable of emitting an UV light;

a first transparent conductive layer including metal or metal oxide formed on an upper surface of the second semiconductor layer;

a second transparent conductive layer including transparent conductive non-metal material formed on the first transparent conductive layer;

a contact layer between the second semiconductor layer and the first transparent conductive layer, wherein the second semiconductor layer comprises Al x Ga 1-x N, and the contact layer comprises Al y Ga 1-y N, 0<x, y≤1, and x>y; and

a first electrode formed on the first semiconductor layer and a second electrode formed on the second transparent conductive layer, wherein the second electrode is devoid of contacting the first transparent conductive layer from a cross-section of the light-emitting device, and wherein the first transparent conductive layer is continuously formed over the upper surface of the second semiconductor layer.

2. The light-emitting device of claim 1 , wherein the metal oxide comprises a work function between 4.5 eV and 7 eV.

3. The light-emitting device of claim 1 , wherein the metal oxide comprises a metal comprising a first oxidation state and a second oxidation state.

4. The light-emitting device of claim 1 , wherein the UV light comprises a wavelength between 100 and 290 nm.

5. The light-emitting device of claim 1 , wherein the second semiconductor layer comprises Al x Ga 1-x N, 0.55<x<0.65 and the contact layer comprises Al y Ga 1-y N, 0.05<y<0.1.

6. The light-emitting device of claim 1 , wherein the first transparent conductive layer comprises a sheet resistance larger than a sheet resistance of the second transparent conductive layer.

7. The light-emitting device of claim 1 , wherein the second transparent conductive layer comprises a plurality of sub-layers.

8. The light-emitting device of claim 1 , wherein the transparent conductive non-metal material comprises carbon.

9. The light-emitting device of claim 1 , wherein the transparent conductive non-metal material comprises graphene.

10. The light-emitting device of claim 1 , wherein the contact layer comprises p-type dopant, and a dopant concentration of the p-type dopant is between 1*10 19 cm −3 and 8*10 19 cm −3 .

11. The light-emitting device of claim 1 , wherein the first transparent conductive layer comprises a thickness deviation in a range between 5 nm and 2 nm.

12. The light-emitting device of claim 1 , wherein the contact layer comprises p-type dopants, and a dopant concentration of the p-type dopant is between 1*10 20 cm −3 and 2*10 20 cm −3 .

13. The light-emitting device of claim 1 , wherein the second electrode contacts the second transparent conductive layer.

14. The light-emitting device of claim 1 , wherein 0.01≤y≤0.1.

15. The light-emitting device of claim 1 , wherein the contact layer comprises a thickness between 50 Å and 150 Å.

16. The light-emitting device of claim 1 , wherein the second semiconductor layer comprises a thickness between 250 Å and 1000 Å.

17. The light-emitting device of claim 1 , wherein the first transparent conductive layer comprises a thickness between 0.1 nm and 10 nm.