Light emitting device having light extraction structure and method for manufacturing the same
A nitride-based light emitting device capable of achieving an enhancement in emission efficiency and an enhancement in reliability is disclosed. The light emitting device includes a semiconductor layer, and a light extracting layer arranged on the semiconductor layer and made of a material having a refractive index equal to or higher than a reflective index of the semiconductor layer.
1. A light emitting device, comprising:
a reflective electrode;
a semiconductor layer having a multi-layer structure, the semiconductor layer comprising a first-type semiconductor layer on the reflective electrode, a light emitting layer on the first-type semiconductor layer, and a second-type semiconductor layer on the light emitting layer, wherein a distance between the reflective electrode and the light emitting layer corresponds to reinforced interference condition between a light emitted from the light emitting layer and a light reflected by the reflective electrode; and
a light extraction structure on the second-type semiconductor layer.
2. The light emitting device according to claim 1 , wherein the distance corresponds to about an odd multiple of λ/4n, where “λ” represents a wavelength of light emitted from the light emitting layer, and “n” represents a refractive index of the semiconductor layer.
3. The light emitting device according to claim 1 , wherein the reflective electrode includes a multi-layer metal thin film made of Ni or Ag.
4. The light emitting device according to claim 1 , wherein the light emitting layer and the reflective electrode are arranged at positions shorter than a wavelength of light emitted from the light emitting layer.
5. The light emitting device according to claim 1 , wherein the light extraction structure comprises holes or rods formed on the second-type semiconductor layer.
6. The light emitting device according to claim 5 , wherein the light extraction structure has a periodicity “a” of 800 nm, the holes have a depth of 225 nm, the rods have a height of 225 nm, and radius of the holes is 0.25a.
7. The light emitting device according to claim 6 , wherein the light extraction structure has a periodicity “a” of 800 nm, the holes have a depth of 225 nm, the rods have a height of 225 nm, the holes or the rods have a diameter of 0.35a, and the light extraction structure has air filling-factor of 0.4.
8. The light emitting device according to claim 1 , further comprising a support layer, wherein the reflective electrode is arranged on the support layer.
9. The light emitting device according to claim 8 , wherein the support layer includes a metal or semiconductor.
10. The light emitting device according to claim 1 , further comprising a second-type electrode on a portion of the second-type semiconductor layer, wherein a pattern of the light extraction structure is not formed on a region where the second-type electrode is arranged.
11. The light emitting device according to claim 1 , wherein the reflective electrode has a reflectance of 50% or more.
12. The light emitting device according to claim 1 , wherein the light emitting layer has a thickness of 0.05λ/n to 0.25λ/n.
13. The light emitting device according to claim 1 , wherein the light extraction structure comprises holes or rods formed on the semiconductor layer.
14. The light emitting device according to claim 13 , wherein the holes have a depth of 300 to 3,000 nm, and the rods have a height of 300 to 3,000 nm.
15. The light emitting device according to claim 14 , wherein the holes or rods have a diameter of 0.25a to 0.45a where “a” represents an average periodicity of the light extraction structure.
16. The light emitting device according to claim 1 , wherein the light extraction structure has an average periodicity of 0.8 to 5 μm.
17. The light emitting device according to claim 1 , wherein a p-type semiconductor layer is arranged between the reflective electrode and the light emitting layer.
18. The light emitting device according to claim 1 , wherein the light extraction structure comprises the same material as that of the semiconductor layer.
19. The light emitting device according to claim 1 , wherein a refractive index of the light extraction structure is higher than a refractive index of the semiconductor layer.
20. The light emitting device according to claim 1 , wherein the reflective electrode includes a metal of Al or Ag.
21. The light emitting device according to claim 1 , further comprising a transparent electrode disposed between the reflective electrode and the first-type semiconductor layer.
22. The light emitting device according to claim 1 , wherein the reflective electrode is a single layer having ohmic characteristic.
23. The light emitting device according to claim 1 , further comprising a second-type electrode on the light extraction structure such that the second-type electrode is electrically connected to the second-type semiconductor layer.
24. The device of claim 1 , wherein the distance corresponds to a thickness of the first type semiconductor layer.