Direct investigation of localized leakage currents in GaN-on-sapphire pn-diodes.

The reliability and robustness of GaN devices continues to suffer from the influence of high dislocation densities. Our group has previously linked dislocations with current leakage paths. In this study, we investigated the localized electroluminescence (EL) signals of these leakage paths in reverse biased GaN pn-diodes grown on a sapphire substrate for their electrical and structural properties. We show that EL signal correlated leakage currents can be modeled by trap-assisted-tunneling (TAT) through segregated impurities at a dislocation. Leakage currents in devices without these leakage paths can be modeled by the Poole-Frenkel (PF) and phonon-assisted-tunneling (PAT) mechanisms. Additionally, we show that this reverse bias leakage, that has historically been attributed to specific dislocation types, cannot be attributed to a specific Burgers vector type.