Gallium nitride semiconductor substrate
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 single 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 mirror 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 axis 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 nitride semiconductor, the gallium nitride substrate, wherein:
the primary surface has an off-angle, the off-angle being formed by c-axis of the gallium nitride substrate with an axis perpendicular to the primary surface, and the off-angle being not less than 0.15 degrees, and
a c-face of the gallium nitride substrate is concave or convex, a curvature radius of R of a C-plane of the gallium nitride substrate being equal to or more than 1.5 meters.
2. The gallium nitride substrate according to claim 1 , wherein a maximum distance between one position and another position on an edge of the primary surface is equal to or greater than 10 millimeters.
3. The gallium nitride substrate according to claim 1 , wherein the primary surface is equal to or greater than an area of 2-inch diameter circle.
4. A gallium nitride substrate with a primary surface for epitaxial growth of a III nitride semiconductor, the gallium nitride substrate, wherein:
the primary surface has an off-angle, the off-angle being formed by c-axis of the gallium nitride substrate with an axis perpendicular to the primary surface, and the off-angle being less than 2 degrees, and
a c-face of the gallium nitride substrate is concave or convex, a curvature radius of R of a C-plane of the gallium nitride substrate being equal to or more than 1.5 meters.
5. The gallium nitride substrate according to claim 4 , wherein a maximum distance between one position and another position on an edge of the primary surface is equal to or greater than 10 millimeters.
6. The gallium nitride substrate according to claim 4 , wherein the primary surface is equal to or greater than an area of 2-inch diameter circle.
7. A gallium nitride substrate with a primary surface for epitaxial growth of a III nitride semiconductor, the gallium nitride substrate, wherein:
the primary surface has an off-angle,
the primary surface has an inner area, an outer area surrounding the inner area, the outer area having at least one of a point or portion in which the off-angle is equal to zero, and
a c-face of the gallium nitride substrate is concave or convex, a curvature radius of R of a C-plane of the gallium nitride substrate being equal to or more than 1.5 meters.
8. The gallium nitride substrate according to claim 7 , wherein a maximum distance between one position and another position on an edge of the primary surface is equal to or greater than 10 millimeters.
9. The gallium nitride substrate according to claim 7 , wherein the primary surface is equal to or greater than an area of 2-inch diameter circle.
10. The gallium nitride substrate according to claim 1 , wherein, when the III nitride semiconductor film is formed on the primary surface of the gallium nitride substrate, a surface morphology of a surface of the III nitride semiconductor includes no six-sided pyramid pattern.
11. The gallium nitride substrate according to claim 4 , wherein, when the III nitride semiconductor film is formed on the primary surface of the gallium nitride substrate, a surface morphology of as surface of the III nitride semiconductor includes no scratch-like pattern.