Nitride semiconductor substrate, semiconductor laminate, laminated structure, method for manufacturing nitride semiconductor substrate and method for manufacturing semiconductor laminate
To provide a technique of increasing a radius of curvature of (0001) plane, and narrowing an off-angle distribution, there is provided a nitride semiconductor substrate containing a group III nitride semiconductor crystal and having a main surface in which a nearest low index crystal plane is (0001) plane, wherein (0001) plane in one of a direction along <1-100> axis and a direction along <11-20> axis orthogonal to the <1-100> axis, is curved in a concave spherical shape with respect to the main surface, and a radius of curvature of the (0001) plane in one of the direction along the <1-100> axis and the direction along the <11-20> axis orthogonal to the <1-100> axis is different from a radius of curvature of at least a part of the (0001) plane in the other direction.
1. A nitride semiconductor substrate containing a group III nitride semiconductor crystal and having a main surface in which a nearest low index crystal plane is (0001) plane,
wherein the (0001) plane in one of a direction along <1-100> axis and a direction along <11-20> axis orthogonal to the <1-100> axis, is curved in a concave spherical shape with respect to the main surface, and
a radius of curvature of the (0001) plane in one of the direction along the <1-100> axis and the direction along the <11-20> axis orthogonal to the <1-100> axis is different from a radius of curvature of at least a part of the (0001) plane in the other direction.
2. The nitride semiconductor substrate according to claim 1 , wherein the (0001) plane in the other one of the direction along the <1-100> axis and the direction along the <11-20> axis has convex portions and concave portions alternately arranged in the other direction.
3. The nitride semiconductor substrate according to claim 1 , wherein the (0001) plane in the direction along the <11-20> axis is curved in a concave spherical shape with respect to the main surface, and
a radius of curvature of at least a part of the (0001) plane in the direction along the <1-100> axis is larger than a radius of curvature of the (0001) plane in the direction along the <11-20> axis.
4. The nitride semiconductor substrate according to claim 3 , wherein the radius of curvature of at least a part of the (0001) plane in the direction along the <1-100> axis is 1.5 times or more the radius of curvature of the (0001) plane in the direction along the <11-20> axis.
5. The nitride semiconductor substrate according to claim 1 , wherein the (0001) plane in the direction along the <1-100> axis is curved in a concave spherical shape with respect to the main surface, and
a radius of curvature of at least a part of the (0001) plane in the direction along the <11-20> axis is larger than a radius of curvature of the (0001) plane in the direction along the <1-100> axis.
6. The nitride semiconductor substrate according to claim 5 , wherein the radius of curvature of at least a part of the (0001) plane in the direction along the <11-20> axis is 1.5 times or more the radius of curvature of the (0001) plane in the direction along the <1-100> axis.
7. The nitride semiconductor substrate according to claim 1 , wherein the radius of curvature of the (0001) plane is 10 m or more.
8. The nitride semiconductor substrate according to claim 1 , wherein when a diameter of the nitride semiconductor substrate is D (mm), in the main surface, a maximum minimum difference in off-angles of the <0001> axis of the crystal with respect to a normal of the main surface is within D/500°.
9. The nitride semiconductor substrate according to claim 1 , wherein when there are a plurality of dislocations extending in a direction along the <0001> axis, and when a lattice constant in the <11-20> axial direction is defined as a and a lattice constant of the <0001> axis is defined as c, a size of Burgers vector of each of the plurality of dislocations is any one of a, a+c, and c.