Light-emitting device

1. A light-emitting device, comprising:

an active structure, the active structure comprising alternate well layers and barrier layers, wherein each of the well layers comprises multiple different elements of group VA;

a first semiconductor layer of first conductivity type and a second semiconductor layer of second conductivity type sandwiching the active structure;

an intermediate layer interposed between the first semiconductor layer and the active structure, wherein the first semiconductor layer has a first band gap, the second semiconductor layer has a second band gap, the well layer has a third band gap, and the intermediate layer has a fourth band gap, wherein the first band gap and the second band gap are both larger than the fourth band gap, and the fourth band gap is larger than the third band gap, and the intermediate layer has a thickness larger than a thickness of the barrier layer; and

a first window layer on the first semiconductor layer, wherein the intermediate layer comprises Al z1 Ga 1-z1 As, the first window layer comprises Al z2 Ga 1-z2 As, and z 1 >z 2 .

2. The light-emitting device according to claim 1 , wherein one of the well layers has a band gap and one of the barrier layers has a band gap, and a difference between the band gap of the well layer and the band gap of the barrier layer is between 0.4 eV and 0.6 eV.

3. The light-emitting device according to claim 2 , wherein the difference between the band gap of the well layer and the band gap of the barrier layer is between 0.5 eV and 0.55 eV.

4. The light-emitting device according to claim 1 , wherein one of the well layers and one of the barrier layers each has a residual compressive stress, and the residual compressive stress of the well layer is larger than the residual compressive stress of the barrier layer.

5. The light-emitting device according to claim 4 , wherein the difference between the residual compressive stress of the well layer and the residual compressive stress of the barrier layer is not more than 2500 ppm.

6. The light-emitting device according to claim 4 , wherein the difference between the residual compressive stress of the well layer and the residual compressive stress of the barrier layer is not more than 2000 ppm.

7. The light-emitting device according to claim 1 , wherein the first semiconductor layer comprises Al z3 Ga 1-z3 As, and 0.4≤z 1 ≤z 3 .

8. The light-emitting device according to claim 4 , wherein the intermediate layer has a thickness not less than 200 nm.

9. The light-emitting device according to claim 1 , wherein the intermediate layer has a thickness between 200 and 2000 nm.

10. The light-emitting device according to claim 1 , wherein one of the well layers and/or one of the barrier layers is undoped.

11. The light-emitting device according to claim 1 , wherein all of the well layers and all of the barrier layers are undoped.

12. The light-emitting device according to claim 1 , wherein one of the well layers comprises In x Ga 1-x As 1-y P y , x≠0,0.001≤y≤0.1 and z≠0.

13. The light-emitting device according to claim 12 , wherein the 0.04≤x≤0.08.

14. The light-emitting device according to claim 12 , wherein the 0.01≤y≤0.08.

15. The light-emitting device according to claim 12 , wherein the 0.05≤y≤0.07.

16. The light-emitting device according to claim 1 , wherein the number of the well layers or the barrier layers is between ten and thirty.

17. The light-emitting device according to claim 1 , wherein the barrier layers comprises AlzGa 1-z As, wherein z is between about 0.35 and 0.45.

18. The light-emitting device according to claim 1 , wherein the active structure emits a radiation of a dominant wavelength between 750 and 1050 nm both inclusive.

19. The light-emitting device according to claim 1 , wherein each well layer has a thickness between 3 nm and 8 nm.

20. The light-emitting device according to claim 1 , wherein each barrier layer has a thickness between 8 nm and 20 nm.