Reverse Leakage Current Hysteresis in GaN Schottky Barrier Diodes Interpreted in Terms of a Trap Energy Band

The hysteresis cycles observed in the reverse leakage current measured at low temperatures in GaN-on-sapphire Schottky barrier diodes (SBDs) have been deeply studied and interpreted in terms of trap-assisted tunneling (TAT) compatible with the existence of a trap energy band (TEB) near the metal-semiconductor interface. The analysis of the energies for which the maximum tunneling current occurs, both direct and through this trap band, allows us to explain the behaviors found at different temperatures. Starting from empty trap states by previous illumination, transient current measurements performed under different preconditioning voltages evidence a progressive partial filling/release of the trap energy levels, confirmed as well by pulsed measurements. Captured/released electrons modify the number of trap states available for tunneling and thus the current level. As a consequence, tunneling processes in the go and return paths take place through levels with different occupations within the TEB, originating the hysteresis cycle.