Suppression of charge trapping in ON-state operation of AlGaN/GaN HEMTs by Si-rich passivation

In this paper, we investigate the charge trapping in power AlGaN/GaN high electron mobility transistors (HEMTs) which occurs in ON-state operation (VDS = 40 V, VGS = 0 V, IDS = 0.18 A/mm). By analysing the dynamic ON-resistance (RON) after OFF-state and ON-state stress in devices with different SiNx passivation stoichiometries, we find that this charge trapping can be largely suppressed by a high Si concentration passivation. Both potential probe and electroluminescence (EL) measurements further confirm that the stress can induce negative charge trapping in the gate-drain access region. It is shown that EL is generated as expected under the field plates at the gate edge, but is obscured by the field plates and is actually emitted from the device near the drain edge; hence care is required when using EL alone as a guide to the location of the high field region in the device. From temperature-dependent dynamic RON transient measurements, we determine that the apparent activation energy of the measured "trap" response is around 0.48 eV, and infer that they are located in the heavily carbon-doped GaN layer. Using the leaky dielectric model, we explain the response in terms of the hopping transport from the same substitutional carbon acceptor buffer dopants.