Method of fabricating single crystal gallium nitride semiconductor substrate, nitride gallium semiconductor substrate and nitride semiconductor epitaxial 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 method of fabricating a single crystal gallium nitride substrate, the method comprising 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 being grown by vapor phase epitaxy in a direction of a predetermined axis, each predetermined plane being inclined to the predetermined axis, each substrate having a mirror polished primary surface, the primary surface having a first area and a second area, the first area being between an edge of the substrate and a line 3 millimeter away from the edge, the first area surrounding the second area, an axis perpendicular to the primary surface forming an off-angle with c-axis of the substrate, the off-angle taking a minimum value at a first position in the first area of the primary surface.
2. The method according to claim 1 , wherein an axis perpendicular to the primary surface forms an angle greater than zero with c-axis of the substrate.
3. The method according to claim 1 , wherein the off angle takes a maximum value at a second position on the primary surface, and the off angle makes substantially monotonic change on a segment from the first position to the second position.
4. The method according to claim 1 , wherein the off angle takes a nonzero constant value on a curve on the primary surface and the curve terminates at the edge of the primary surface.
5. A method of fabricating a single crystal gallium nitride substrate, the method comprising the step of:
slicing an ingot of single crystal gallium nitride along predetermined planes to prepare one or more single crystal gallium nitride slices, each predetermined plane being inclined to a predetermined axis, the ingot of single crystal gallium nitride being grown by vapor phase epitaxy, and each single crystal gallium nitride slice having a slice surface; and
performing at least one process of polishing and grinding of the slice surface to form one or more single crystal gallium nitride substrates, each substrate having a primary surface, the primary surface having a first area and a second area, the first area being between an edge of the substrate and a line 3 millimeters away from the edge, the first area surrounding the second area, an axis perpendicular to the primary surface forming an off-angle with c-axis of the substrate, the off-angle taking a minimum value at a first position in the first area of the primary surface.
6. The method according to claim 5 , wherein an axis perpendicular to the primary surface forms an angle greater than zero with c-axis of the substrate.
7. The method according to claim 5 , wherein the off angle takes a maximum value at a second position on the primary surface, and the off angle makes substantially monotonic change on a segment from the first position to the second position.
8. The method according to claim 5 , wherein the off angle takes a nonzero constant value on a curve on the primary surface and the curve terminates at the edge of the primary surface.