P-doping of group-III-nitride buffer layer structure on a heterosubstrate
An epitaxial group-ill-nitride buffer-layer structure is provided on a heterosubstrate, wherein the buffer-layer structure has at least one stress-management layer sequence including an interlayer structure arranged between and adjacent to a first and a second group-ill-nitride layer, wherein the inter layer structure comprises a group-ill-nitride interlayer material having a larger band gap than the materials of the first and second group-ill-nitride layers, and wherein a p-type-dopant-concentration profile drops, starting from at least 1×1018 cm-3, by at least a factor of two in transition from the interlayer structure to the first and second group-ill-nitride layers.
1. An epitaxial group-III-nitride buffer-layer structure on a silicon, wherein the buffer-layer structure comprises at least one stress management layer sequence including an interlayer structure arranged between and adjacent to a first group-III-nitride layer and a second group-III-nitride layer,
wherein the 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 interlayer structure to the first and second group-III-nitride layers,
wherein a thickness of the first group-III-nitride layer is between 300 nm and 2000 nm, and
wherein a thickness of the second group-III-nitride layer is between 300 nm and 1500 nm.
2. The buffer-layer structure according to claim 1 , wherein the interlayer structure comprises a single layer and has a thickness between 10 nm and 50 nm.
3. The buffer-layer structure according to claim 1 , wherein the interlayer structure is made of AlGaN, or wherein the interlayer structure uses AlN, or AlInN, or AlInGaN.
4. The buffer-layer structure according to claim 1 , wherein the stress-management layer sequence is made of GaN—AlGaN—GaN.
5. The buffer-layer structure according to claim 1 , wherein the p-type-dopant-concentration profile drops in transition from the 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, or wherein a carbon concentration in the interlayer structure is three orders of magnitude higher than in the first and second group-III-nitride layers.
6. The buffer-layer structure according to claim 1 , wherein the interlayer structure comprises three different layers, a first group-III-nitride interlayer, a second group-III-nitride interlayer and a third group-III-nitride interlayer that have a thickness between 20 nm and 200 nm.
7. The buffer-layer structure according to claim 6 , wherein the second and third group-III-nitride interlayers comprise a constant aluminum content.
8. The buffer-layer structure according to claim 6 , wherein the second and third group-III-nitride interlayers and the first and second group-III-nitride layers are made of GaN, and wherein the first group-III-nitride interlayer is formed of AlGaN.
9. The buffer-layer structure according to claim 6 , wherein the second and third group-III-nitride interlayers comprise a gradient in the aluminum content.
10. The buffer-layer structure according to claim 9 , wherein the second and third group-III-nitride interlayers and the first and second group-III-nitride layers are made of GaN, and wherein an aluminum content of the first group-III-nitride interlayer increases from 10% at the interface to the second group-III-nitride interlayer to 70% at the interface to the third group-III-nitride interlayer.
11. The buffer-layer structure according to claim 10 , wherein a hole concentration caused by p-doping is constant within an entirety of the interlayer structure, and in the first, second, and third group-III-nitride interlayers.
12. The buffer-layer structure according to claim 10 , wherein the hole concentration caused by p-doping is 1×10 18 cm −3 within the entirety of the interlayer structure, and in the first, second, and third group-III-nitride interlayers.
13. The buffer-layer structure according to claim 9 , wherein a hole concentration caused by p-doping for the second and third group-III-nitride interlayers is higher than a hole concentration of the first group-III-nitride interlayer.
14. The buffer-layer structure according to claim 9 , wherein the first group-III-nitride interlayer is unintentionally doped.
15. The buffer-layer structure according to claim 9 , wherein a hole concentration caused by p-doping 5×10 18 cm −3 in the second and third group-III-nitride interlayers.
16. The buffer-layer structure according to claim 1 , wherein the first and second group-III-nitride layers are only unintentionally p-doped.
17. The buffer-layer structure of claim 1 , wherein the p-type dopant is carbon or magnesium, or a combination of carbon and magnesium.
18. The buffer layer structure according to claim 1 , further comprising at least two stress management layer sequences, wherein a second stress management layer sequence arranged at a larger distance from the substrate than a first stress management layer sequence has a second interlayer structure.
19. The buffer layer structure according to claim 18 , 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 the interlayers of the interlayer structure, a p-type dopant concentration in at least one of the interlayers of the interlayer structure, a material composition of at least one of the interlayers of the interlayer structure, and/or a number of interlayers in the interlayer structure.
20. The buffer layer structure according to claim 1 , wherein an additional group-III-nitride layer is deposited on top of the buffer-layer structure, wherein the additional group-III-nitride layer has a graded p-type-dopant-concentration profile, wherein the p-type dopant concentration is higher in a first section of the additional group-III-nitride layer adjacent to the buffer-layer structure than in a second section of the additional group-III-nitride layer further away from the buffer-layer structure.
21. The buffer layer structure according to claim 1 , further comprising a buffer stack deposited between a heterosubstrate and the at least one stress management layer sequence, the buffer stack comprising:
a compositionally graded AlGaN buffer layer having a Ga fraction increasing with increasing distance from the heterosubstrate, or
a superlattice formed by a stack of alternating group-III-nitride layers of two kinds,
wherein the buffer stack has a p-type-dopant concentration of at least 1×10 17 cm −3 .
22. A group-III-nitride device, a FET, a normally-on or a normally-off HEMT or MIS-HEMT, a Schottky diode, a PIN diode, or a LED comprising an epitaxial group-III-nitride buffer layer structure on a heterosubstrate according to claim 1 .