Light-emitting device and manufacturing method thereof

1. A light-emitting device, comprising:

a substrate comprising:

a base comprising a main surface; and

a plurality of protrusions separately disposed on the main surface, wherein the plurality of protrusions and the base comprise different materials; and

a semiconductor stack on the main surface, the semiconductor stack comprising a side wall, wherein an included angle between the side wall and the main surface is an obtuse angle;

wherein the main surface comprises a peripheral area surrounding the semiconductor stack, and the peripheral area is devoid of the plurality of protrusions formed thereon; and

wherein the base comprises a plurality of mesas on the main surface, and each one of the plurality of protrusions is disposed on a respective one of the plurality of mesas.

2. The light-emitting device according to claim 1 , wherein the plurality of protrusions comprises a first material and the base comprises a second material; and a refractive index of the first material is smaller than that of the second material.

3. The light-emitting device according to claim 1 , further comprising a plurality of holes between the side wall and the main surface, and the holes are devoid of the plurality of protrusions formed therein.

4. The light-emitting device according to claim 1 , wherein the base comprises a side wall and the side wall of the base comprises a rough region connecting the main surface.

5. The light-emitting device according to claim 1 , wherein in a top view, the substrate comprises a long edge and a short edge, and a ratio of a length of the long edge to a length of the short edge is greater than 2.

6. The light-emitting device according to claim 1 , further comprising a first electrode and a second electrode on the semiconductor stack, wherein the substrate comprises a pair of short edges opposite to each other, and the first electrode and the second electrode are adjacent to the pair of short edges, respectively.

7. The light-emitting device according to claim 1 , wherein the main surface is a plane and the plurality of protrusions are on the plane.

8. The light-emitting device according to claim 1 , wherein the semiconductor stack comprises a buffer layer, a first semiconductor layer, an active layer, and a second semiconductor layer sequentially on the main surface, wherein the buffer layer is conformably formed on the plurality of protrusions and the main surface.

9. The light-emitting device according to claim 1 , wherein the side wall of the semiconductor stack comprises a plurality of sub-side walls.

10. The light-emitting device according to claim 9 , wherein an included angle between the plurality of sub-side walls is 100-175 degrees.

11. The light-emitting device according to claim 1 , wherein a height of one of the plurality of mesas on the peripheral area is larger than a height of one of the plurality of mesas under the semiconductor stack.

12. The light-emitting device according to claim 1 , wherein in a top view, one of the plurality of mesas on the peripheral area and one of the plurality of mesas under the semiconductor stack have different shapes.

13. The light-emitting device according to claim 12 , wherein each of the plurality of mesas comprises a bottom; and

wherein in a top view, the bottom of one of the plurality of mesas on the peripheral area is polygonal and the bottom of one of the plurality of mesas under the semiconductor stack is circular.

14. The light-emitting device according to claim 1 , wherein parts of the plurality of mesas are disposed on the peripheral area.

15. The light-emitting device according to claim 1 , wherein the plurality of mesas comprises the same material as that of the base.

16. The light-emitting device according to claim 1 , a divergence angle of the light-emitting device is less than or equal to 130 degrees.

17. The light-emitting device according to claim 1 , wherein each one of the plurality of mesas comprises a flat top surface.