Nitride semiconductor substrate
A nitride semiconductor substrate is provided, having a concave or convex warpage on a front surface side, wherein when a rear surface side is placed on a flat surface, an average roughness of the rear surface at a part not in contact with the flat surface and at a part where a height from the flat surface to the rear surface is a prescribed value or more is set to be greater than an average roughness of the rear surface at a part where the height from the flat surface including a part in contact with the flat surface to the rear surface is less than the prescribed value.
1. A nitride semiconductor substrate, comprising:
a front surface as a surface on which a nitride semiconductor crystal is grown;
a rear surface as a surface of an opposite side of the front surface, and
warping so that the front surface side is a concave surface, and the rear surface side is a convex surface,
wherein when mounted on a flat surface of a susceptor having the flat surface so that the rear surface is opposed to the flat surface, the rear surface has:
a rear surface center part which has a part in contact with the flat surface, and a part not in contact with the flat surface, with a distance from the flat surface being less than 5 μm, and
a rear surface outer peripheral part which is a part positioned outside of the rear surface center part and not in contact with the flat surface, with a distance from the flat surface being 5 μm or more, and
wherein an arithmetic average roughness of the rear surface outer peripheral part is larger than an arithmetic average roughness of the rear surface center part.
2. The nitride semiconductor substrate according to claim 1 , wherein the arithmetic average roughness of the rear surface outer peripheral part is from twice to four times the arithmetic average roughness of the rear surface center part.
3. The nitride semiconductor substrate according to claim 1 , wherein the arithmetic average roughness of the rear surface outer peripheral part gradually increases in a direction in which a distance between the rear surface and the flat surface increases.
4. The nitride semiconductor substrate according to claim 1 , wherein the arithmetic average roughness of the rear surface center part is set to 0.3 μm, and the arithmetic average roughness of the rear surface outer peripheral part is set to from 0.6 μm to 1.2 μm.
5. The nitride semiconductor substrate according to claim 1 , wherein the arithmetic average roughness of the rear surface center part is set to 0.3 μm, and the arithmetic average roughness of the rear surface outer peripheral part is set to from 0.7 μm to 1.1 μm.
6. The nitride semiconductor substrate according to claim 1 , wherein the arithmetic average roughness of the rear surface center part is set to 0.3 μm, and the arithmetic average roughness of the rear surface outer peripheral part is set to 0.6 μm.