Wafer-level nondestructive inspection of substrate off-angle and net donor concentration of the n−-drift layer in vertical GaN-on-GaN Schottky diodes

Abstract

In the mass production of GaN-on-GaN vertical power devices, a nondestructive simple inspection of the net donor concentration (ND − NA) of the n−-drift layer in the range of 1015 cm−3 is required. In this study, we demonstrate the wafer-level nondestructive inspection of GaN Schottky barrier diode epi-structures grown by metal organic vapor phase epitaxy (MOVPE) on free-standing GaN substrates. We found that the normalized yellow (YL) photoluminescence peak intensity of the near band edge (NBE), IYL/INBE, is strongly related to the acceptor concentration NA of the n−-drift layer. This means that the ND − NA of the n−-drift layer can be inspected by photoluminescence measurement at a high speed, when Si concentration is not varying across the GaN wafers. Noncontact capacitance–voltage and secondary ion mass spectrometry measurements were used to investigate the cause of ND − NA variation across the GaN wafers. The discrepancy between C and NA indicates that compensation could be due to another electron trap.