Light-emitting device
A light-emitting device, includes a substrate structure, including a base portion having a surface and a plurality of protrusions regularly formed on the base portion; a buffer layer covering the plurality of protrusions and the surface; and III-V compound semiconductor layers formed on the buffer layer; wherein one of the plurality of protrusions includes a first portion and a second portion formed on the first portion and the first portion is integrated with the base portion; and wherein the base portion includes a first material and the first portion includes the first material.
1. A light-emitting device, comprising:
a substrate structure, comprising a base portion having a surface and a plurality of protrusions regularly formed on the base portion;
a buffer layer covering the plurality of protrusions and the surface; and
III-V compound semiconductor layers formed on the buffer layer;
wherein one of the plurality of protrusions comprises a first portion and a second portion formed on the first portion and the first portion is integrated with the base portion;
wherein the base portion comprises a first material and the first portion comprises the first material,
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 buffer layer is formed on and contacts the first side surface, the second side surface and the surface of the base portion.
2. The light-emitting device according to claim 1 , wherein the second portion comprises a second material which is different from the first material and a refractive index of the second material is smaller than a refractive index of the first material.
3. The light-emitting device according to claim 1 , wherein the first portion of 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.
4. The light-emitting device according to claim 2 , wherein the buffer layer comprises a third material which is different from the second material.
5. The light-emitting device according to claim 4 , wherein the buffer layer comprises aluminum nitride.
6. The light-emitting device according to claim 2 , wherein the second material comprises SiO 2 .
7. The light-emitting device according to claim 1 , wherein the first material comprises sapphire and the surface is c-plane of the sapphire.
8. The light-emitting device according to claim 1 , wherein the first portion comprises a planar top and the second portion is formed on and contacts the planar top.
9. The light-emitting device according to claim 1 , wherein an arrangement of the plurality of protrusions has a period and the period is between 1 μm and 3 μm both inclusive.
10. The light-emitting device according to claim 1 , wherein in a cross-sectional view, an included angle between a side surface of one of the plurality of protrusions and the surface of the base portion is less than 65 degrees.
11. The light-emitting device according to claim 1 , wherein a thickness of the buffer layer is greater than 5 nm and not more than 50 nm.
12. The light-emitting device according to claim 1 , wherein a three-dimensional shape of one of the plurality of protrusions comprises a dome, a cone or a pyramid.
13. The light-emitting device according to claim 1 , wherein in a cross-sectional view, 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.
14. The light-emitting device according to claim 1 , wherein the buffer layer is conformably formed on the first side surface, the second side surface and the surface of the base portion.