Group III nitride substrate with oxygen gradient, method of making, and method of use

A free-standing nonpolar or semipolar crystal, comprising a group III metal and nitrogen, wherein the free-standing nonpolar or semipolar crystal comprises:

• a wurtzite crystal structure;
• a first surface having a crystallographic orientation within 30 degrees of {1 0 −1 0}, a maximum dimension greater than 5 millimeters in a first direction, the first direction comprising a projection of [0 0 0 1] on the first surface, and a maximum dimension greater than 15 millimeters in a second direction orthogonal to the first direction;
• a second surface on an opposite side of the crystal from the first surface, wherein a separation distance between the first surface and the second surface is between 100 micrometers and 1000 micrometers;
• and
• an average concentration of stacking faults on the first surface below 103 cm−1,
• wherein the crystal is characterized by an oxygen concentration having a minimum value between 2×1017 cm−3 and 1×1019 cm−3 at a first position along the first surface and increasing along all points in the [0 0 0 1] direction to a maximum value between 1×1018 cm−3 and about 5×1019 cm−3 at a second position along the first direction, the second position being separated from the first position by a distance between 1 millimeter and 25 millimeters along the first direction.