Electrode structure, and semiconductor light-emitting device having the same

1. A semiconductor light emitting device comprising:

a transparent substrate;

an electron injection layer which is formed on the transparent substrate and formed of N-type GaN-based semiconductor;

an active layer which is formed on a first region of the electron injection layer;

a hole injection layer which is formed on the active layer and formed of P-type GaN-based semiconductor;

a first electrode structure which is formed on the hole injection layer and concurrently providing a high reflectivity and a low contact resistance;

a second electrode structure which is formed on a second region of the electron injection layer; and

a circuit substrate which is electrically connected with the first and second electrode structures,

wherein the first electrode structure comprises a contact metal structure which is mesh- or island-shaped on the hole injection layer to expose a surface portion of the hole injection layer, and a reflective layer which covers the contact metal structure and the exposed surface portion of the hole injection layer, at least an upper portion of the reflective layer being made of silver (Ag) or aluminum (Al),

an area ratio of the contact metal structure to the first electrode structure satisfies a following inequality:

0.4 ≦A pd /A total <1

where A pd is the surface area of the contact metal structure contacting the hole injection layer, and A total is the entire area of the first electrode structure contacting the hole injection layer, and

the first and second electrode structures are flip-chip bonded to the circuit substrate to extract light through the transparent substrate.

2. The light emitting device of claim 1 , wherein the area ratio satisfies an inequality of 0.4≦A pd /A total ≦0.9.

3. The light emitting device of claim 1 , wherein the thickness of the contact metal structure is less than 200 nm.

4. The light emitting device of claim 1 , wherein the hole injection layer is formed of P-type GaN.

5. The light emitting device of claim 1 , wherein the contact metal structure is made of Pd.

6. The light emitting device of claim 1 , wherein the reflective layer is made of Ag or Al.

7. The light emitting device of claim 1 , wherein the reflective layer comprises a dielectric layer formed on the exposed surface portion of the hole injection layer, and a reflective metal layer made of Ag or Al which covers the contact metal structure and the dielectric layer.

8. The light emitting device of claim 7 , wherein the thickness of the dielectric layer is λ/(4n), where λ is a wavelength of light emitted from the light emitting device and n is a refractive index of the dielectric.

9. The light emitting device of claim 7 , wherein the refractive index of the dielectric layer is from 1.1 to 2.3.

10. The light emitting device of claim 7 , wherein the dielectric layer is made of SiO 2 or Si 3 N 4 .

11. An electrode structure used in a flip-chip GaN-based semiconductor light emitting device having an active layer and a hole injection layer formed on the active layer, the electrode structure being formed on the hole injection layer, the electrode structure comprising:

a contact metal structure which is mesh- or island-shaped on the hole injection layer to expose a surface portion of the hole injection layer; and

a reflective layer which covers the contact metal structure and the exposed surface portion of the hole injection layer, at least an upper portion of the reflective layer being made of silver (Ag) or aluminum (Al),

wherein an area ratio of the contact metal structure to the first electrode structure satisfies a following inequality:

0.4 ≦A pd /A total <1

where A pd is the surface area of the contact metal structure contacting the hole injection layer, and A total is the entire area of the first electrode structure contacting the hole injection layer.

12. The electrode structure of claim 11 , wherein the area ratio satisfies an inequality of 0.4≦A pd /A total ≦0.9.

13. The electrode structure of claim 11 , wherein the thickness of the contact metal structure is less than 200 nm.

14. The electrode structure of claim 11 , wherein the hole injection layer is formed of P-type GaN.

15. The electrode structure of claim 11 , wherein the contact metal structure is made of Pd.

16. The electrode structure of claim 11 , wherein the reflective layer is made of Ag or Al.

17. The electrode structure of claim 11 , wherein the reflective layer comprises a dielectric layer formed on the exposed surface portion of the hole injection layer, and a reflective metal layer made of Ag or Al which covers the contact metal structure and the dielectric layer.

18. The electrode structure of claim 17 , wherein the thickness of the dielectric layer is λ/(4n), where λ is a wavelength of light emitted from the light emitting device and n is a refractive index of the dielectric.

19. The electrode structure of claim 17 , wherein the refractive index of the dielectric layer is from 1.1 to 2.3.

20. The electrode structure of claim 17 , wherein the dielectric layer is made of SiO 2 or Si 3 N 4 .