Wafer-Level Donor Uniformity Improvement by Substrate Off-Angle Control for Vertical GaN-on-GaN Power Switching Devices

In the mass production of GaN-on-GaN vertical power devices, the wafer-level uniformity of net donor concentration, N_D - N_A, of the n^--drift layer in around 10¹⁵ cm^-3 is an important factor because it determines the breakdown voltage. A nondestructive simple inspection is also required. In this paper, we demonstrated the wafer-level nondestructive inspection of a GaN Schottky barrier diode epi-layer and improved the wafer-level net donor uniformity by controlling the off-angle of GaN substrates. Epi-structures were grown by metal-organic vapor phase epitaxy on free-standing GaN substrates with various off-angles and deviations. The variation in N_D - N_A was carefully analyzed using non-contact capacitance-voltage measurement and photoluminescence. Silicon and carbon concentrations were confirmed by secondary ion mass spectrometry. We found that the normalized yellow luminescence peak intensity is almost linearly related to the acceptor concentration. A carbon related variation in the acceptor concentration (N_A) resulted in the non-uniformity of N_D - N_A, which is found to be related to the substrate off-angle of the wafer. The N_D - N_A uniformity can be improved by minimizing variation in the off-angle. Criteria of the GaN substrate off-angle deviation for power applications are discussed.