Nitride semiconductor epitaxial substrate and nitride semiconductor device
There is provided a nitride semiconductor epitaxial substrate having a group III nitride semiconductor layer with C-plane as a surface, grown on a substrate via a buffer layer of the group III nitride semiconductor containing Al, wherein the buffer layer has an inversion domain on the surface.
1. A nitride semiconductor epitaxial substrate, comprising:
a buffer layer grown on a substrate, composed of a group III nitride semiconductor containing Al, and having a thickness between 10-300 nm; and
a group III nitride semiconductor layer grown on the buffer layer,
wherein in a surface of the buffer layer an inversion domain having N-polar is irregularly distributed, and
the group III nitride semiconductor layer is configured so that a layer grown on the inversion domain on the surface of the buffer layer is embedded by a layer grown on a region other than the inversion domain on the surface of the buffer layer, an inversion domain does not exist on a surface of the group III nitride semiconductor layer, the surface of the group III nitride semiconductor layer is a C-plane of group III polarity, a dislocation density on the surface of the group III nitride semiconductor layer is 5×10 8 cm −2 or less, and the dislocation density on the surface of the group III nitride semiconductor layer is lower than a dislocation density of a region in which the inversion domain does not exist on the surface of the buffer layer.
2. The nitride semiconductor epitaxial substrate according to claim 1 , wherein a surface density of the inversion domain on the surface of the buffer layer is in a range of 1×10 4 cm −2 or more and 1×10 11 cm −2 or less.
3. The nitride semiconductor epitaxial substrate according to claim 1 , wherein at least one impurity selected from the group consisting of chlorine (Cl), boron (B), and sulfur (S) is added to the buffer layer, with a concentration of 1×10 15 cm −3 or more, so that the inversion domain irregularly appears on the surface of the buffer layer.
4. The nitride semiconductor epitaxial substrate according to claim 1 , wherein half width values of (0002) plane diffraction, (0004) plane diffraction, and (10-12) plane diffraction in measurement of X-ray rocking curves of the group III nitride semiconductor layer, are respectively 300 seconds or less, 300 seconds or less, and 500 seconds or less.
5. The nitride semiconductor epitaxial substrate according to claim 1 , wherein the group III nitride semiconductor layer has a thickness of 5 μm or more, with no cracks on the surface.
6. A nitride semiconductor device having a device structure formed on the nitride semiconductor epitaxial substrate of claim 1 .
7. The nitride semiconductor epitaxial substrate according to claim 1 , wherein the buffer layer is an Al x Ga 1-x N (0.5≦x≦1) layer.
8. The nitride semiconductor epitaxial layer substrate according to claim 1 , wherein the inversion domain is distributed irregularly over an entire surface of the buffer layer.
9. The nitride semiconductor epitaxial substrate according to claim 1 , wherein a diameter of the substrate is 4 inches.
10. The nitride semiconductor epitaxial substrate according to claim 1 , wherein a diameter of the substrate is 4 inches, and a surface density of the inversion domain on the surface of the buffer layer is in a range of 1×10 6 cm −2 or more and 1×10 9 cm −2 or less.
11. A nitride semiconductor epitaxial substrate, comprising:
a buffer layer grown on a substrate, and composed of AIN; and
a group III nitride semiconductor layer grown on the buffer layer,
wherein in a surface of the buffer layer, an inversion domain having N-polar is irregularly distributed, and
the group III nitride semiconductor layer is configured so that a layer grown on the inversion domain on the surface of the buffer layer is embedded by a layer grown on a region other than the inversion domain on the surface of the buffer layer, an inversion domain does not exist on a surface of the group III nitride semiconductor layer, the surface of the group III nitride semiconductor layer is a C-plane of group III polarity, and the dislocation density on the surface of the group III nitride semiconductor layer is lower than a dislocation density of a region in which the inversion domain does not exist on the surface of the buffer layer.
12. The nitride semiconductor epitaxial substrate according to claim 11 , wherein the inversion domain is distributed irregularly over an entire surface of the buffer layer.
13. The nitride semiconductor epitaxial substrate according to claim 11 , wherein a diameter of the substrate is 4 inches.
14. The nitride semiconductor epitaxial substrate according to claim 11 , wherein a diameter of the substrate is 4 inches, and a surface density of the inversion domain on the surface of the buffer layer is in a range of 1×10 6 cm −2 or more and 1×10 9 cm −2 or less.