Method of manufacturing a light-emitting device

1. A method of manufacturing a light-emitting device, comprising:

providing a substrate comprising a top surface;

forming a precursor layer on the top surface;

removing a portion of the precursor layer and a portion of the substrate from the top surface to form a base portion and a plurality of protrusions regularly arranged on the base portion;

forming a buffer layer on the base portion and the plurality protrusions; and

forming a III-V compound cap layer on the buffer layer;

wherein one of the plurality of protrusions comprises a first portion and a second portion formed on the first portion;

wherein the first portion is integrated with the base portion and has a first material which is the same as that of the base portion; and

wherein the buffer layer contacts side surfaces of the plurality of protrusions and a surface of the base portion.

2. The method according to claim 1 , wherein:

the first portion comprises a first side surface and the second portion comprises a second side surface connecting the first side surface; and

wherein the side surface of the one of the plurality of protrusions comprises the first side surface and the second side surface.

3. The method according to claim 1 , further comprising a recess between the plurality of protrusions, and wherein the III-V compound cap layer covers the buffer layer and is formed in the recess.

4. The method according to claim 3 , wherein a thickness of the III-V compound cap layer is greater than 1 μm and not more than 3.5 μm.

5. The method according to claim 1 , wherein the portion of the precursor layer is removed and the other portion of the precursor layer kept on the top surface forms the second portion of the one of the protrusions.

6. The method according to claim 1 , wherein the buffer layer is conformably formed on the side surfaces of the plurality of protrusions and the surface of the base portion.

7. The method according to claim 1 , wherein the first portion of the one of the plurality of protrusions has a height H 1 and the one of the plurality of protrusions has a height H; wherein a ratio of H 1 to H is between 1% and 30% both inclusive.

8. The method according to claim 1 , wherein the buffer layer is formed on the surface of the base portion by physical vapor deposition.

9. The method according to claim 8 , wherein a method of forming the III-V compound semiconductor layers is different from physical vapor deposition.

10. The method according to claim 1 , wherein the precursor layer comprises a second material which is different from the first material.

11. The method according to claim 1 , wherein III-V compound cap layer comprises a III-V compound semiconductor having an energy gap smaller than that of the buffer layer.

12. The method according to claim 1 , wherein in a cross-sectional view, the one of the plurality of protrusions comprises an arc which protrudes outward, and two ends of the arc are connected to form a pseudo chord; and wherein a maximum distance between the arc and the pseudo chord is greater than 0 μm and not greater than 0.5 μm.

13. The method according to claim 1 , wherein in a cross-sectional view, an included angle between the side surface of one of the plurality of protrusions and the surface of the base portion is not greater than 65 degrees.

14. The method according to claim 1 , wherein the one of the plurality protrusions comprises an upper plane and a lower plane opposite to the upper plane, and the lower plane is closer to the surface of the base portion than the upper plane, wherein a ratio of an area of the upper plane to an area of the lower plane is greater than zero and not more than 0.3.

15. The method according to claim 1 , wherein the light-emitting device has a full width at half maximum (FWHM) of smaller than 250 arcsec in accordance with a (102) XRD rocking curve.

16. The method according to claim 1 , wherein one of the plurality of protrusions has a height not greater than 1.5 μm.