P-doping of group-III-nitride buffer layer structure on a heterosubstrate

1. An epitaxial group-III-nitride buffer-layer structure comprising:

a substrate;

a back barrier layer;

an active layer; and

a first stress management layer sequence comprising a first interlayer structure, a first group-III-nitride layer, and a second group-III-nitride layer, the first interlayer structure arranged between and adjacent to the first and second group-III-nitride layers,

wherein the first interlayer structure comprises a group-III-nitride interlayer material having a larger band gap than the materials of the first and second group-III-nitride layers,

wherein a p-type-dopant-concentration profile drops, starting from at least 1×10 18 cm −3 , by at least a factor of two in transition from the first interlayer structure to the first and second group-III-nitride layers, and

wherein, the first stress management layer sequence is arranged between the substrate and the active layer.

2. The buffer-layer structure according to claim 1 , wherein the back barrier layer is made of AIGaN and has a graded carbon concentration.

3. The buffer-layer structure according to claim 2 , wherein a carbon concentration of back barrier layer is highest at an interface between back barrier layer and a third group-III-nitride layer.

4. The buffer-layer structure according to claim 1 , wherein the p-type-dopant concentration profile drops in transition from the first interlayer structure to the first and second group-III-nitride layers by at least one order of magnitude or by at least two orders of magnitude.

5. The buffer-layer structure according to claim 1 , further comprising a second stress management layer sequence wherein the second stress management layer sequence that has a second interlayer structure is arranged at a larger distance from the substrate than the first stress management layer sequence.

6. The buffer-layer structure according to claim 5 , wherein the second interlayer structure differs from the first interlayer structure in at least one of the following:

a layer thickness of at least one of interlayers of the first interlayer structure and the second interlayer structure,

a p-type dopant concentration in at least one of the interlayers of the first interlayer structure and the second interlayer structure,

a material composition of at least one of the interlayers of the first interlayer structure and the second interlayer structure, and/or

a number of interlayers in the first interlayer structure and the second interlayer structure.

7. The buffer-layer structure according to claim 1 , wherein an additional group-III-nitride layer is deposited on top of the buffer-layer structure and wherein the additional layer has a graded p-type-dopant-concentration profile, wherein the p-type dopant concentration is higher in a first section of the additional layer adjacent to the buffer-layer structure than in a second section of the additional layer further away from the buffer-layer structure.

8. The buffer-layer structure according to claim 1 , further comprising an intermediate layer deposited between the substrate and the first stress management layer sequence, the intermediate layer comprising a compositionally graded AIGaN buffer layer having a Ga fraction increasing with increasing distance away from the substrate.

9. The buffer-layer structure according to claim 8 , wherein the buffer stack has a p-type-dopant concentration of at least 1×10 17 cm −3 .

10. The buffer-layer structure according to claim 1 , further comprising a buffer stack deposited between the substrate and the first stress management layer sequence, the buffer stack comprising a superlattice formed by a stack of alternating group-III-nitride layers of two kinds.

11. The buffer-layer structure according to claim 10 , wherein the buffer stack has a p-type-dopant concentration of at least 1×10 17 cm −3 .

12. The buffer-layer structure according to claim 1 , wherein the substrate is a silicon substrate or a heterosubstrate.

13. The buffer-layer structure according to claim 1 , wherein the back barrier layer is arranged between the active layer and the first stress management layer sequence.

14. The buffer-layer structure according to claim 1 , wherein the buffer layer structure is an epitaxial group-III-nitride buffer layer structure formed in a group-III-nitride device, a transistor, a normally-on or normally-off HEMT or MIS-HEMT, a Schottky diode, a PIN diode, or a LED.

15. The buffer-layer structure according to claim 14 , wherein the transistor is a field effect transistor.