High efficiency light emitting diode

1. A light emitting diode comprising:

a substrate;

a semiconductor stack disposed on the substrate, the semiconductor stack comprising a p-type compound semiconductor layer, an active layer, and an n-type compound semiconductor layer;

a reflective metal layer disposed between the substrate and the semiconductor stack and in ohmic contact with the p-type compound semiconductor layer, the reflective metal layer comprising a groove exposing a portion of the semiconductor stack;

a first electrode pad disposed on the n-type compound semiconductor layer;

an electrode extension extending from the first electrode pad and disposed over the groove; and

a first insulating layer disposed between a side surface of the first electrode pad and a side surface of the semiconductor stack,

wherein the n-type compound semiconductor layer comprises an n-type contact layer, and

wherein the n-type contact layer has an Si doping concentration of 5 to 7×10 18 /cm 3 and a thickness in the range of 5 to 10 μm.

2. The light emitting diode of claim 1 , wherein the n-type compound semiconductor layer further comprises a superlattice layer disposed between the n-type contact layer and the active layer.

3. The light emitting diode of claim 2 , wherein the superlattice layer comprises alternately stacked InGaN layers and GaN layers.

4. The light emitting diode of claim 3 , wherein the superlattice layer has a higher resistivity than that of the n-type contact layer.

5. The light emitting diode of claim 1 , further comprising a second insulating layer disposed in the groove and contacting the portion of the semiconductor stack exposed by the groove.

6. The light emitting diode of claim 5 , further comprising a barrier metal layer disposed between the reflective metal layer and the substrate.

7. The light emitting diode of claim 6 , wherein the reflective metal layer comprises plates separated by the groove.

8. The light emitting diode of claim 1 , wherein a first portion of the semiconductor plates stack comprises a roughened surface, and

wherein the first insulating layer covers the roughened surface and comprises a concave-convex surface corresponding to the roughened surface.

9. The light emitting diode of claim 8 , wherein a second portion of the semiconductor stack comprises a flat surface, and the first electrode pad and the electrode extension are disposed on the flat surface.

10. The light emitting diode of claim 9 , wherein the electrode extension contacts the flat surface of the semiconductor stack.

11. A light emitting diode, comprising:

a substrate;

a semiconductor stack disposed on the substrate, the semiconductor stack comprising a p-type compound semiconductor layer, an active layer, and an n-type compound semiconductor layer;

a reflective metal layer disposed between the substrate and the semiconductor stack and in ohmic contact with the p-type compound semiconductor layer, the reflective metal layer and comprising a groove exposing a portion of the semiconductor stack;

a first electrode pad disposed on the n-type compound semiconductor layer;

an electrode extension extending from the first electrode pad and disposed over the groove; and

a first insulating layer disposed between a side surface of the first electrode pad and a side surface the semiconductor stack,

wherein the n-type compound semiconductor layer comprises an n-type contact layer and a first recovering layer disposed between the n-type contact layer and the active layer,

wherein the first recovering layer comprises an undoped layer or a low doped layer comprising a doping concentration lower than that of the n-type contact layer, and

wherein the n-type contact layer has a thickness in the range of 4.5 to 10 μm.

12. The light emitting diode of claim 11 , wherein the first recovering layer has a thickness in the range of 100 to 200 nm.

13. The light emitting diode of claim 12 , further comprising an electron injection layer disposed between the first recovering layer and the active layer.

14. The light emitting diode of claim 13 , further comprising

a second recovering layer disposed between the first recovering layer and an electron supplementation layer; and

an electron supplementation layer disposed between the first and second recovering layers.

15. The light emitting diode of claim 14 , further comprising a superlattice layer disposed between the electron injection layer and the active layer.

16. The light emitting diode of claim 11 , further comprising a second insulating layer disposed in the groove and contacting the portion of the semiconductor stack exposed by the groove.

17. The light emitting diode of claim 16 , further comprising a barrier metal layer disposed between the reflective metal layer and the substrate.

18. The light emitting diode of claim 17 , wherein the reflective metal layer comprises plates separated by the groove.

19. The light emitting diode of claim 11 , wherein a first portion of the semiconductor stack comprises a roughened surface, and

wherein the first insulating layer covers the roughened surface and comprises a concave-convex surface corresponding to the roughened surface.

20. The light emitting diode of claim 19 , wherein a second portion of the semiconductor stack comprises a flat surface, and the first electrode pad and the electrode extension are disposed on the flat surface.

21. The light emitting diode of claim 20 , wherein the electrode extension contacts the flat surface of the semiconductor stack.