Mechanism of the reverse gate leakage in AlGaN/GaN high electron mobility transistors

The off-state gate current in AlGaN/GaN high electron mobility transistors is shown to arise from two parallel gate to substrate tunneling paths: a direct path, and a path via deep traps, which are distributed throughout the AlGaN layer and spread over an energy band. A model to calculate this current is given, which shows that trap-assisted tunneling dominates below T similar to 500 K, and direct tunneling (thermionic field emission) dominates at higher temperatures. A model fit to experimental results yields the following fabrication process sensitive parameters: trap concentration of similar to10(13)-10(15) cm(-3), and trap bandwidth of similar to50%-70% of the barrier height located 0.4-0.55 V below the conduction band edge. (C) 2003 American Institute of Physics.