A Comparative Study on P-GaN HEMTs with Schottky/Ohmic Gate Contacts

P-GaN gate AlGaN/GaN high electron mobility transistor (HEMT) is currently the mainstream solution to realize enhancement mode GaN-based power electronic devices, but the influence of Schottky contact or ohmic contact on the device characteristics is still an issue to be further comparatively studied. In this paper, the impacts of Schottky and ohmic-type gate contacts on device performances such as transfer characteristics, transconductance and breakdown voltage of p-GaN gate AlGaN/GaN HEMT devices were studied by TCAD simulation. In Schottky-gate devices, the gate leakage is lower, and a larger threshold voltage (>6V) can be obtained by adjusting the parameters of the p-GaN cap layer, but as the threshold voltage increases, the drain current density will be correspondingly suppressed. In contrast, the threshold voltage of ohmic-gate devices is relatively stable and the drain current density is larger. In addition, ohmic-gate devices exhibit superior voltage withstand capability, but ohmic-type gate devices suffer serious gate leakage problem. Then the influence of Schottky- and ohmic- gate contacts on the stability of p-GaN gate AlGaN/GaN HEMT is studied. It is found that the threshold voltage of both devices is unstable.