Off-state leakage current reduction in AlGaN/GaN high electron mobility transistors by combining surface treatment and post-gate annealing
We report on the reduction of off-state leakage current in AlGaN/GaN high electron mobility transistors (HEMTs) by a two-step process combining pre-gate surface treatment and post-gate annealing (PGA), which suppressed the two leakage paths, namely, lateral surface leakage and vertical tunneling leakage, separately. The lateral surface leakage current, which was mainly induced by the high-density trap states generated during the device isolation etching process, was significantly reduced by a low power O2-plasma and HCl surface treatment process. The PGA process reduced the vertical tunneling leakage current by improving the Schottky contact quality of the transistor gate. Consequently, the device off-state leakage current was decreased by about 7 orders of magnitude and no degradation was introduced to the on-state performance, leading to a high on/off current ratio of 1010 and steep subthreshold slope (SS) of 62 mV/dec. The origin and leakage suppression mechanisms are also investigated and discussed in detail.