Light-emitting device
A light-emitting device is provided. The light-emitting device comprises The light-emitting device comprises a light-emitting stack comprising a first semiconductor layer, a second semiconductor layer and an active layer between the first semiconductor layer and the second semiconductor layer; and a third semiconductor layer on the light-emitting stack and comprising a first sub-layer, a second sub-layer and a roughened surface, wherein the first sub-layer has the same composition as that of the second sub-layer, and the second sub-layer is farther from the light-emitting stack than the first sub-layer; wherein the first sub-layer and the second sub-layer each comprises a Group III element and a Group V element, and an atomic ratio of the Group III element to the Group V element of the first sub-layer is less than an atomic ratio of the Group III element to the Group V element of the second sub-layer.
1. A light-emitting device, comprising:
a light-emitting stack comprising a first semiconductor layer, a second semiconductor layer and an active layer between the first semiconductor layer and the second semiconductor layer; and
a third semiconductor layer on the light-emitting stack and comprising a first sub-layer, a second sub-layer and a roughened surface, wherein the first sub-layer has the same composition as that of the second sub-layer, and the second sub-layer is farther from the light-emitting stack than the first sub-layer;
wherein a concentration Al of the second sub-layer is higher than that of the first sub-layer,
wherein the first sub-layer and the second sub-layer each comprises a Group III element and a Group V element, and an atomic ratio of the Group III element to the Group V element of the first sub-layer is less than an atomic ratio of the Group III element to the Group V element of the second sub-layer.
2. The light-emitting device according to claim 1 , wherein the third semiconductor layer further comprises a first portion and a second portion, and the second portion comprises the roughened surface.
3. The light-emitting device according to claim 2 , wherein the first portion has a first thickness t 1 , and the second portion has a second thickness between 0.3*t 1 and 0.85*t 1 .
4. The light-emitting device according to claim 3 , wherein the first thickness is between 2000 nm and 4000 nm both inclusive.
5. The light-emitting device according to claim 2 , wherein the second portion substantially surrounds the first portion.
6. The light-emitting device according to claim 1 , wherein an atomic percentage of the Group III element of the second sub-layer is gradually changed in a direction toward the light-emitting stack.
7. The light-emitting device according to claim 1 , wherein the first sub-layer comprises (Al y Ga (1-y) ) 1-x In x P, the second sub-layer comprises (Al z Ga (1-z) ) 1-x In x P, and a difference between z and y is between 0.1 and 0.5 both inclusive.
8. The light-emitting device according to claim 1 , wherein the first sub-layer comprises (Al y Ga (1-y) ) 1-x In x P, 0.3≤y≤0.5, the second sub-layer comprises (Al z Ga (1-z) ) 1-x In x P, 0≤x<1, 0.5≤z≤0.7, and a difference between z and y is not less than 0.1.
9. The light-emitting device according to claim 1 , wherein the first sub-layer comprises (Al y Ga (1-y) ) 1-x In x P, 0≤x<1, 0.3≤y≤0.5, and the second sub-layer comprises (Al z Ga (1-z) ) 1-x In x P, 0≤x<1, 0.4≤z≤0.7, wherein z is gradually decreased in a direction toward the light-emitting stack.
10. The light-emitting device according to claim 1 , wherein the second sub-layer is on the first sub-layer and comprises an upper surface, and the roughened surface is between the light-emitting stack and the upper surface.
11. The light-emitting device according to claim 10 , further comprising a first electrode on the upper surface of the second sub-layer.
12. The light-emitting device according to claim 1 , wherein the second sub-layer has a thickness smaller than a thickness of the first sub-layer.
13. The light-emitting device according to claim 1 , wherein the roughened surface has an irregular surface texture.
14. The light-emitting device according to claim 1 , wherein the second sub-layer has an element having an atomic percentage gradually changed in a direction toward the light-emitting stack.
15. A light-emitting device, comprising:
a light-emitting stack comprising a first semiconductor layer, a second semiconductor layer and an active layer between the first semiconductor layer and the second semiconductor layer; and
a third semiconductor layer on the light-emitting stack and comprising a first sub-layer, a second sub-layer and a roughened surface, wherein the first sub-layer has the same composition as that of the second sub-layer, and the second sub-layer is farther from the light-emitting stack than the first sub-layer;
wherein the first sub-layer comprises Al x Ga (1-x) As, and the second sub-layer comprises Al y Ga (1-y) As, wherein an atomic ratio of Al to Ga in the first sub-layer is less than an atomic ratio of Al to Ga in the second sub-layer.
16. The light-emitting device according to claim 15 , wherein 0.3≤x≤0.7.
17. The light-emitting device according to claim 15 , wherein 0.4≤y≤0.8.
18. The light-emitting device according to claim 15 , wherein a difference between x and y is between 0.1 and 0.5 both inclusive.
19. The light-emitting device according to claim 15 , wherein y is gradually decreased in a direction toward the light-emitting stack.
20. The light-emitting device according to claim 15 , wherein the second sub-layer has a thickness smaller than a thickness of the first sub-layer.