Hole Virtual Gate Model Explaining Surface-Related Dynamic RON in p-GaN Power HEMTs

Dynamic on-resistance ( R ON ) affects the stability of p-GaN power HEMTs. In Schottky-gate HEMTs, dynamic R ON is associated to either electron trapping at device surface or dynamic effects occurring in the buffer. However, in p-GaN HEMTs the floating p-GaN region can have an additional role on dynamic R ON , due to removal/injection of holes from/into the barrier with relatively long time constants, which can be erroneously interpreted as a reliability issue. In this letter, we present a model to explain the dynamic R ON due to surface-related effects in p-GaN power HEMTs. The model, called 'hole virtual gate', attributes the experimentally observed R ON instability due to negative/positive gate bias stress (NGS/PGS) to the charging/discharging of surface traps in the AlGaN barrier by the removal/injection of holes through the gate metal/p-GaN Schottky junction. We verify the validity of the model by means of calibrated numerical simulations, that correlate the activation energy EA ≈ 0.4 eV of both R ON increase/decrease during NGS/PGS to the thermal ionization energy of traps in the barrier.