Gallium nitride semiconductor substrate with semiconductor film formed therein
A method of fabricating a single crystal gallium nitride substrate the step of cutting an ingot of single crystal gallium nitride along predetermined planes to make one or more signal crystal gallium nitride substrates. The ingot of single crystal gallium nitride is grown by vapor phase epitaxy in a direction of a predetermined axis. Each predetermined plane is inclined to the predetermined axis. Each substrate has a minor polished primary surface. The primary surface has a first area and a second area. The first area is between an edge of the substrate and a line 3 millimeter away from the edge. The first area surrounds the second area. An qaxis perpendicular to the primary surface forms an off-angle with c-axis of the substrate. The off-angle takes a minimum value at a first position in the first area of the primary surface.
1. A gallium nitride substrate with a primary surface for epitaxial growth of a III-group nitride semiconductor, wherein:
the primary surface has a first area and a second area,
an off-angle formed by a c-axis of the gallium nitride substrate with an axis perpendicular to the primary surface is minimum in the second area,
a c-face of the gallium nitride substrate is concave or convex, and
a curvature radius of R of C-plane of the gallium nitride substrate is equal to or more than 1.5 meters.