Buffer-trap and surface-state effects on gate lag in AlGaN/GaN HEMTs

Two-dimensional simulation of turn-on characteristics of Al-GaN/GaN HEMTs is performed in which both buffer traps and surface states are considered. It is studied how the so-called gate lag is affected by these factors. It is shown that gate lag due to buffer traps can occur because in the off state where the gate voltage is negative, electrons are injected into the buffer layer and captured by the traps, leading to more negatively charged buffer layer. It is also shown that gate lag due to an electron-trap-type surface state can occur only when electron's gate tunneling is considered.