Semiconductor device

1. A semiconductor device comprising:

a first type semiconductor structure comprising a first lattice constant, a first side and a second side opposite to the first side;

an active structure on the first side and emitting a radiation having a peak wavelength between 1000 nm and 2000 nm; and

a contact layer on the second side and comprising a second lattice constant,

wherein a difference between the second lattice constant and the first lattice constant is at least 0.5%, and

wherein the contact layer comprises a III-V group semiconductor material.

2. The semiconductor device of claim 1 , wherein the active structure comprises III-V group semiconductor materials.

3. The semiconductor device of claim 2 , wherein the first type semiconductor structure comprises a III-V group semiconductor material.

4. The semiconductor device of claim 1 , further comprising a buffer layer between the contact layer and the first type semiconductor structure,

wherein the buffer layer comprises a quaternary semiconductor compound.

5. The semiconductor device of claim 1 , further comprising a buffer layer between the contact layer and the first type semiconductor structure,

wherein the contact layer comprises a first dopant with a first doping concentration and the buffer layer comprises the first dopant with a second doping concentration, the active structure comprises the first dopant with a third doping concentration, and the second doping concentration is between the first doping concentration and the third doping concentration.

6. The semiconductor device of claim 1 , further comprising:

a buffer layer between the contact layer and the first type semiconductor structure; and

a window layer between the contact layer and the buffer layer.

7. The semiconductor device of claim 6 , wherein the window layer comprises the same material as or different from that of the contact layer.

8. The semiconductor device of claim 6 , wherein the window layer has a third lattice constant and a difference between the first lattice constant and the third lattice constant is lower than 0.5%.

9. The semiconductor device of claim 6 , wherein the window layer has a thickness thicker than that of the contact layer.

10. The semiconductor device of claim 1 , wherein the contact layer has a surface with a roughing structure.

11. The semiconductor device of claim 1 , wherein the contact layer has a band gap higher than that of the active structure.

12. The semiconductor device of claim 1 , further comprising a base, a first electrode and a second electrode, wherein the first electrode and the second electrode are located on the same side of the base.

13. The semiconductor device of claim 1 , further comprising a base, wherein the first type semiconductor structure is located between the contact layer and the base.

14. The semiconductor device of claim 13 , further comprising a first electrode away from the base, and the contact layer directly contacts the first electrode.

15. A package structure comprising:

a packaging mount;

a semiconductor device of claim 1 on the packaging mount; and

an encapsulating structure covering the semiconductor device.

16. The semiconductor device of claim 1 , wherein the contact layer has a thickness less than that of the first type semiconductor structure.

17. The semiconductor device of claim 1 , wherein the active structure comprises a first element and a second element different from the first element, and the contact layer does not comprise the first element and the second element.

18. The semiconductor device of claim 17 , further comprising a base and a second type structure between the active structure and the base,

wherein the first type semiconductor and the second type structure comprise the first element.

19. The semiconductor device of claim 17 , wherein the contact layer comprises a dopant with a doping concentration between 2×10 18 /cm 3 and 5×10 19 /cm 3 .

20. The semiconductor device of claim 1 , wherein the contact layer has a thickness between 5 nm and 100 nm.