Crystal layered structure and method for manufacturing same, and semiconductor element
Provided is a crystal layered structure having a low dislocation density on the upper surface of a nitride semiconductor layer on a Ga 2 O 3 substrate, and a method for manufacturing the same. In one embodiment, there is provided a crystal layered structure including: a Ga 2 O 3 substrate; a buffer layer comprising an Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on the Ga 2 O 3 substrate; and a nitride semiconductor layer comprising an Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y +z=1) crystal including oxygen as an impurity on the buffer layer. The oxygen concentration in a region having a thickness of no less than 200 nm on the nitride semiconductor layer on the side towards the Ga 2 O 3 substrate is no less than 1.0×10 18 /cm 3 .
1. A crystal layered structure, comprising:
a Ga 2 O 3 substrate;
a buffer layer comprising an Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on the Ga 2 O 3 substrate; and
a nitride semiconductor layer comprising an Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal containing oxygen as an impurity on the buffer layer,
wherein an oxygen concentration in a region on a side of the Ga 2 O 3 substrate of the nitride semiconductor layer, region having a thickness of not less than 200 nm, is not less than 1.0×10 18 cm 3 .
2. The crystal layered structure according to claim 1 , wherein the nitride semiconductor layer has a dislocation density of less than 1.0×10 9 /cm 2 on a surface thereof opposite the Ga 2 O 3 substrate.
3. The crystal layered structure according to claim 1 , wherein an oxygen concentration in a region on the side of the Ga 2 O 3 substrate of the nitride semiconductor layer, the region having a thickness of not less than 500 nm, is not less than 1.0×10 18 /cm 3 .
4. The crystal layered structure according to claim 1 , wherein the oxygen concentration in the region is not less than 5.0×10 18 /cm 3 .
5. The crystal layered structure according to claim 1 , wherein the Al x Ga y In z N crystal of the buffer layer comprises an AlN crystal.
6. The crystal layered structure according to claim 1 , wherein the Al x Ga y In z N crystal of the nitride semiconductor layer comprises a GaN crystal.
7. A method for manufacturing a crystal layered structure, comprising:
a step of forming a buffer layer by growing a first Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on a Ga 2 O 3 substrate; and
a step of forming a nitride semiconductor layer by growing a second Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on the buffer layer,
wherein the second Al x Ga y In z N crystal is initially grown at a first temperature of not more than 1000° C. and is then grown at a second temperature higher than the first temperature in the step of forming the nitride semiconductor layer, and
wherein the second Al x Ga y In z N crystal grown at the first temperature is not less than 200 nm in thickness.
8. The method for manufacturing a crystal layered structure according to claim 7 , wherein the second Al x Ga y In z N crystal grown at the first temperature is not less than 500 nm in thickness.
9. The method for manufacturing a crystal layered structure according to claim 7 , wherein the first Al x Ga y In z N crystal comprises an AlN crystal.
10. The method for manufacturing a crystal layered structure according to claim 7 , wherein the second Al x Ga y In z N crystal comprises a GaN crystal.
11. A crystal layered structure, comprising:
a Ga 2 O 3 substrate;
a buffer layer comprising an Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on the Ga 2 O 3 substrate; and
a nitride semiconductor layer comprising an Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on the buffer layer,
wherein a percentage of a surface of the Ga 2 O 3 substrate covered with the buffer layer in a region immediately below the nitride semiconductor layer is not less than 10% and less than 100%, and
wherein a portion of the nitride semiconductor layer is in contact with the surface of the Ga 2 O 3 substrate.
12. The crystal layered structure according to claim 11 , wherein the percentage is not more than 90%.
13. The crystal layered structure according to claim 11 , wherein the buffer layer comprises the Al x Ga y In z N crystal arranged in an island pattern on the Ga 2 O 3 substrate.
14. The crystal layered structure according to claim 11 , wherein the buffer layer comprises the Al x Ga y In z N crystal in a film shape comprising a hole.
15. The crystal layered structure according to claim 11 , wherein the Al x Ga y In z N crystal of the buffer layer comprises an AlN crystal.
16. The crystal layered structure according to claim 11 , wherein the Al x Ga y In z N crystal of the nitride semiconductor layer comprises a GaN crystal.
17. A semiconductor element, comprising:
the crystal layered structure according to claim 11 ,
wherein the Ga 2 O 3 substrate and the nitride semiconductor layer are configured to allow electrical conduction therethrough.
18. A method for manufacturing a crystal layered structure, comprising:
a step of forming a buffer layer by growing a first Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on a Ga 2 O 3 substrate so as to partially cover a surface of the Ga 2 O 3 substrate; and
a step of foaming a nitride semiconductor layer by growing a second Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on the buffer layer,
wherein a percentage of a surface of the Ga 2 O 3 substrate covered with the buffer layer in a region immediately below the nitride semiconductor layer is not less than 10% and less than 100%, and
wherein a portion of the nitride semiconductor layer is in contact with the surface of the Ga 2 O 3 substrate.
19. The method for manufacturing a crystal layered structure according to claim 18 , wherein the percentage is not more than 90%.
20. The method for manufacturing a crystal layered structure according to claim 18 , wherein the buffer layer is formed by growing the first Al x Ga y In z N crystal in an island pattern on the Ga 2 O 3 substrate.
21. The method for manufacturing a crystal layered structure according to claim 18 , wherein the buffer layer is formed by growing the first Al x Ga y In z N crystal in a film shape comprising a hole on the Ga 2 O 3 substrate.
22. The method for manufacturing a crystal layered structure according to claim 18 , wherein the first Al x Ga y In z N crystal comprises an AlN crystal.
23. The method for manufacturing a crystal layered structure according to claim 18 , wherein the second Al x Ga y In z N crystal comprises a GaN crystal.
24. A method for manufacturing a crystal layered structure, comprising:
a step of forming a buffer layer by growing a first Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal at a first temperature on a Ga 2 O 3 substrate of which principal surface is a surface having an oxygen atom arranged in a hexagonal lattice pattern; and
a step of farming a nitride semiconductor layer by growing a second Al x Ga y In z N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) crystal on the buffer layer,
wherein a step of nitriding a surface of the Ga 2 O 3 substrate at a higher temperature than the first temperature is not performed before forming the buffer layer.
25. The method for manufacturing a crystal layered structure according to claim 24 , wherein the Ga 2 O 3 substrate is kept at the first temperature for not more than 10 minutes in a state of being exposed to a nitrogen raw material gas and is then kept at the first temperature in a state of being exposed to the N-raw material gas and an Al raw material gas to grow the second Al x Ga y In z N crystal.
26. The method for manufacturing a crystal layered structure according to claim 24 , wherein the principal surface of the Ga 2 O 3 substrate comprises one of (101), (−201), (301) and (3-10) planes.
27. The method for manufacturing a crystal layered structure according to claim 24 , wherein the first Al x Ga y In z N crystal comprises an AlN crystal.
28. The method for manufacturing a crystal layered structure according to claim 24 , wherein the second Al x Ga y In z N crystal comprises a GaN crystal.