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 interlayer 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-Ill-nitride buffer-layer structure on a heterosubstrate, the buffer-layer structure comprising:
a first and a second group-III-nitride layers; and
a first stress management layer sequence including a 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, and
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.
2. 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.
3. 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 two orders of magnitude.
4. The buffer-layer structure according to claim 1 , wherein the p-type dopant concentration is constant throughout the first interlayer structure.
5. The buffer-layer structure according to claim 1 , wherein the first interlayer structure is a single layer, and wherein the group-III-nitride interlayer material has a homogeneous composition, which has a larger band gap than the first and second group-III-nitride layers, and wherein the concentration of the p-type dopant in the interlayer structure is at least 6×10 18 cm −3 .
6. The buffer-layer structure according to claim 1 , wherein the first interlayer structure comprises a first group-III-nitride interlayer that is arranged between and adjacent to a second group-III-nitride interlayer and a third group-III-nitride interlayer, wherein the first, second and third group-III-nitride interlayer have a respective homogeneous composition, wherein a band gap of the first group-III-nitride interlayer is larger than band gaps of the second group-III-nitride interlayer and the third group-III-nitride interlayer, and wherein the p-type-dopant concentration throughout the interlayer structure is at least 5×10 18 cm −3 .
7. The buffer-layer structure according to claim 1 , wherein the first interlayer structure comprises a first group-III-nitride interlayer that is arranged between and adjacent to a second group-III-nitride interlayer and a third group-III-nitride interlayer, and wherein the first group-III-nitride interlayer is compositionally graded.
8. The buffer-layer structure according to claim 7 , wherein the first group-III-nitride interlayer is made of AlGaN having an Al mole fraction that increases with increasing distance from the heterosubstrate.
9. The buffer-layer structure according to claim 7 , wherein the concentration of the p-type dopant is higher in the second and third group-III-nitride interlayers than in the first group-III-nitride interlayer.
10. The buffer-layer structure according to claim 1 , wherein the first interlayer structure comprises a first group-III-nitride interlayer that is arranged between and adjacent to a second group-III-nitride interlayer and a third group-III-nitride interlayer, and wherein the second group-III-nitride interlayer or the third group-III-nitride interlayer or the second and the third group-III-nitride interlayer are compositionally graded.
11. The buffer-layer structure according to claim 1 , wherein the group-III-nitride interlayer material having a larger band gap additionally has a larger oxygen concentration than either the first or the second group-III-nitride layer, or than both the first and the second group-III-nitride layers.
12. The buffer-layer structure according to claim 1 , wherein the p-type dopant is carbon or magnesium, or a combination of carbon and magnesium.
13. The buffer-layer structure according to claim 1 , wherein the first or the second group-III-nitride layer, or the first and the second group-III-nitride layers has a p-type-dopant concentration between 1×10 16 /cm 3 and 1×10 18 /cm 3 .
14. 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 heterosubstrate than the first stress management layer sequence, has a second interlayer structure.
15. The buffer-layer structure according to claim 14 , 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 first and second interlayer structures, a p-type dopant concentration in at least one of the interlayers of the first and second interlayer structures, a material composition of at least one of the interlayers of the first and second interlayer structures, or a number of interlayers in the first and second interlayer structures.
16. 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 layer has a graded p-type-dopant-concentration profile, and 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.
17. The buffer-layer structure according to claim 1 , wherein the heterosubstrate is either a silicon substrate, a silicon-on-insulator substrate, or a silicon carbide substrate.
18. The buffer-layer structure according to claim 1 , further comprising a buffer stack deposited between the heterosubstrate and the first stress management layer sequence, the buffer stack comprising either 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 .
19. A group-III-nitride device, a field effect transistor, a normally-on or a normally-off HEMT, a 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 .
20. A method for fabricating a p-type doped group-III-nitride buffer layer structure on a heterosubstrate, the method comprising:
fabricating an epitaxial group-III-nitride buffer layer structure on a heterosubstrate, the buffer layer structure comprising a stress management layer sequence including an interlayer structure arranged between and adjacent to a first and a second group-III-nitride layer, and the interlayer structure comprising a group-III-nitride interlayer material having a larger band gap than the materials of the first and second group-III-nitride layers; and
fabricating the stress management layer sequence with a p-type dopant concentration profile, which 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.
21. The method according to claim 20 further comprising, before fabricating the stress management layer sequence, depositing a AlN nucleation layer on the heterosubstrate at a temperature between 800 and 1030° C. by a vapor phase deposition technique using a hydrogen-free carrier gas, and depositing a buffer stack before depositing the stress management layer sequence by using Tetraethylgallium and Trimethylaluminum as precursors at a temperature between 800 and 1030° C., wherein the buffer stack comprises either 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, and wherein the nucleation layer and the buffer stack are fabricated with a p-type dopant concentration of at least 1×10 18 cm −3 .