Semiconductor power device

1. A semiconductor power device, comprising:

a substrate;

a buffer structure formed on the substrate;

a barrier structure formed on the buffer structure;

a channel layer formed on the barrier structure; and

a barrier layer formed on the channel layer;

wherein the barrier structure comprises a first functional layer on the buffer structure, a second functional layer formed between the first functional layer and the buffer structure, a first back-barrier layer on the first functional layer, and an interlayer between the first back-barrier layer and the first functional layer;

wherein a material of the first back-barrier layer comprises Al x1 Ga 1-x1 N, a material of the first functional layer comprises Al x2 Ga 1-x2 N, a material of the interlayer comprises Al x3 Ga 1-x3 N, a material of the second functional layer comprises Al x4 Ga 1-x4 N, wherein 0<x1≤1, 0≤x2≤1, 0≤x3≤1, 0≤x4<1, and x1≠x2;

wherein the first functional layer comprises a first thickness, the second functional layer comprises a second thickness, and the second thickness is greater than the first thickness.

2. The semiconductor power device as claimed in claim 1 , wherein x2>x4.

3. The semiconductor power device as claimed in claim 2 , wherein 0.5≤x1.

4. The semiconductor power device as claimed in claim 1 , wherein the second thickness of the second functional layer is 200 to 1000 nm.

5. The semiconductor power device as claimed in claim 1 , wherein the material of the interlayer is doped.

6. The semiconductor power device as claimed in claim 1 , wherein the material of the second functional layer is doped.

7. The semiconductor power device as claimed in claim 1 , wherein x3 is less than x1 and x2.

8. The semiconductor power device as claimed in claim 7 , wherein x3=0.

9. The semiconductor power device as claimed in claim 1 , wherein a two dimensional electron gas is formed near an interface of the channel layer and the barrier layer.

10. The semiconductor power device as claimed in claim 1 , wherein a thickness of the first back-barrier layer is less than or equal to 20 nm.

11. The semiconductor power device as claimed in claim 1 , further comprising a nucleation structure formed between the substrate and the buffer structure.

12. The semiconductor power device as claimed in claim 11 , wherein a material of the nucleation structure comprises AlN.

13. The semiconductor power device as claimed in claim 1 , wherein the buffer structure comprises a strain structure, and the strain structure comprises a superlattice structure of Al m Ga 1-m N and Al n Ga 1-n N, wherein 0≤m≤1, 0≤n≤1.

14. The semiconductor power device as claimed in claim 1 , wherein the buffer structure comprises a thick layer, a thickness of the thick layer is more than or equal to 2 um, and a material of the thick layer comprises a C-doped or a Fe-doped GaN.

15. The semiconductor power device as claimed in claim 1 , wherein a material of the barrier layer comprises Al k Ga 1-k N, wherein 0<k≤1, and a material of the channel layer comprises GaN.

16. The semiconductor power device as claimed in claim 1 , wherein a thickness of the barrier layer is greater than a thickness of the first back-barrier layer.

17. The semiconductor power device as claimed in claim 16 , wherein a thickness of the interlayer is greater than the thickness of the first back-barrier layer.

18. The semiconductor power device as claimed in claim 17 , wherein a thickness of the interlayer is less than the second thickness of the second functional layer.

19. The semiconductor power device as claimed in claim 18 , wherein a material of the interlayer comprises GaN, and a material of the second functional layer comprises AlGaN or GaN.

20. The semiconductor power device as claimed in claim 1 , further comprises a cap layer formed on the barrier layer.