Light-emitting device and manufacturing method thereof

1. A light-emitting device, comprising:

a substrate having a top surface, wherein the top surface comprises a first portion and a second portion;

a first semiconductor stack comprising a first upper surface and a first side wall, wherein the first semiconductor stack is on the first portion and exposes the second portion; and

a second semiconductor stack comprising a second upper surface and a second side wall, wherein the second semiconductor stack is on the first upper surface and exposes an exposing portion of the first upper surface;

wherein the first side wall and the second portion of the top surface form an acute angle α between thereof, and the second side wall and the exposing portion of the first upper surface form an obtuse angle β between thereof, and

wherein the top surface further comprises an edge and the second portion surrounds the first portion and is between the edge and the first portion, and a narrowest distance between the first portion and the edge is between 1 μm and 25 μm.

2. The light-emitting device according to claim 1 , wherein 30°≤α≤80°.

3. The light-emitting device according to claim 1 , wherein 100°≤β≤170°.

4. The light-emitting device according to claim 1 , further comprising a buffer layer between the first semiconductor stack and the top surface.

5. The light-emitting device according to claim 4 , wherein the buffer layer comprises AlN.

6. The light-emitting device according to claim 4 , wherein the thickness of the buffer is between about 5 nm and about 50 nm.

7. The light-emitting device according to claim 1 , wherein the second semiconductor stack comprises a first semiconductor layer, an active layer on the first semiconductor layer and a second semiconductor layer on the active layer, and the first semiconductor stack and the first semiconductor layer have the same conductive type.

8. The light-emitting device according to claim 7 , further comprising a dislocation stop layer between the substrate and the active layer.

9. The light-emitting device according to claim 8 , wherein an Al concentration of the dislocation stop layer is higher than 10 times an Al concentration of the first semiconductor layer or the first semiconductor stack.

10. The light-emitting device according to claim 8 , wherein the thickness of the dislocation stop layer is between about 0.01 nm and about 1 nm.

11. The light-emitting device according to claim 1 , wherein the first side wall is rougher than the second side wall.

12. The light-emitting device according to claim 1 , wherein a ration of an area of the second portion to an area of the top surface is between about 0.02 and about 0.35.

13. The light-emitting device according to claim 1 , wherein the top surface comprises multiple concavo-convex structures regularly distributed in the first portion and the second portion.

14. The light-emitting device according to claim 1 , wherein the substrate further comprises a side surface and a inclined surface connecting the top surface and the side surface, wherein the inclined surface is rougher than the side surface.

15. The light-emitting device according to claim 14 , wherein the substrate further comprises a border between the inclined surface and the side surface, and the narrowest distance between the border and the top surface is between about 0.5 μm and about 25 μm.