Light-emitting element having a reflective structure with high efficiency

1. A light-emitting device, comprising:

a reflective layer;

a first transparent layer on the reflective layer;

a light-emitting stack comprising an active layer on the first transparent layer;

a second transparent layer between the first transparent layer and the light-emitting stack; and

a cavity in the first transparent layer and without penetrating through the first transparent layer.

2. The light-emitting device as claimed in claim 1 , wherein a width of the cavity which is closer to the light-emitting stack is wider than that of the cavity which is remoter from the light-emitting stack.

3. The light-emitting device as claimed in claim 1 , wherein the first transparent layer comprises a plurality of rods, and each of the rods comprises substantially a cross-sectional shape of a trapezoid.

4. The light-emitting device as claimed in claim 1 , wherein the first transparent layer comprises a first transparent conductive oxide, and the second transparent layer comprises a second transparent conductive oxide different from the first transparent conductive oxide.

5. The light-emitting device as claimed in claim 1 , wherein the second transparent layer forms an ohmic contact with the light-emitting stack.

6. The light-emitting device as claimed in claim 1 , wherein the reflective layer comprises metal material or a DBR (Distributed Bragg Reflector) structure.

7. The light-emitting device as claimed in claim 3 , wherein the rod comprises a truncated cone or a truncated pyramid.

8. The light-emitting device as claimed in claim 3 , wherein the trapezoid comprises a top base larger than ⅓ of a bottom base.

9. The light-emitting device as claimed in claim 1 , wherein the cavity comprises substantially a cross-sectional shape of a triangle or a trapezoid.

10. The light-emitting device as claimed in claim 1 , wherein the reflective layer covers sidewalls of the first transparent layer and the second transparent layer.

11. The light-emitting device as claimed in claim 10 , wherein the light-emitting stack further comprises a first semiconductor layer between the active layer and the second transparent layer, and a second semiconductor layer on the active layer.

12. The light-emitting device as claimed in claim 11 , wherein a part of the first semiconductor layer and the active layer is removed to expose the second semiconductor layer.

13. The light-emitting device as claimed in claim 12 , further comprising a conductive layer contacting the exposed second semiconductor layer, and a bonding pad for a power supply to the light-emitting device electrically coupled to the conductive layer.

14. The light-emitting device as claimed in claim 1 , wherein the cavity has a maximum height, the first transparent layer has a thickness, and the maximum height is less than the thickness.

15. The light-emitting device as claimed in claim 1 , wherein the cavity is an air gap.

16. The light-emitting device as claimed in claim 1 , wherein the first transparent layer has a top surface and a bottom surface opposite to the top surface, the cavity has a bottom face, and the bottom face is between the top surface and the bottom surface of the first transparent layer.

17. The light-emitting device as claimed in claim 1 , wherein the cavity is only in the first transparent layer and without extending into a layer adjacent to the first transparent layer.

18. The light-emitting device as claimed in claim 1 , wherein the first transparent layer comprises a base part and multiple rods on the base part, the multiple rods are substantially separated from each other by the cavity, and the cavity is overlapped with the base part of the first transparent layer in a vertical direction.

19. A light-emitting device, comprising:

a reflective layer;

a first transparent layer on the reflective layer;

a light-emitting stack comprising an active layer on the first transparent layer;

a cavity in the first transparent layer; and

a second transparent layer between the first transparent layer and the light-emitting stack.