Mechanism of surface conduction in the vicinity of Schottky gates on AlGaN/GaN heterostructures

Abstract

Lateral surface leakage current (Is) on an AlGaN/GaN heterostructure was systematically investigated by using a two-parallel gate structure with a gap distance (LGG) of 200 nm–5 µm. The surface current Is systematically increased as LGG decreased. A simple resistive layer conduction that should show 1/LGG dependence failed to account for the drastic increase in Is when LGG was reduced to less than 1 µm. However, no dependence on LGG was seen in vertical current that flows in the Schottky interface. The Is showed a clear temperature dependence proportional to exp(−T −1/3), indicating two-dimensional variable-range hopping through high-density surface electronic states in AlGaN. A pronounced reduction in surface current of almost four orders of magnitude was observed in a sample with SiNx passivation. ©2007 American Institute of Physic