Field- and current-driven degradation of GaN-based power HEMTs with p-GaN gate: Dependence on Mg-doping level

Within this paper we investigate the degradation of GaN-HEMTs with p-GaN gate submitted to stress at forward gate bias. We studied the effect of both constant-voltage stress and short-pulse stress (induced by TLP, Transmission Line Pulser); devices having three different Mg-doping levels (ranging from 2.1 . 10(19)/cm(3) to 2.9 . 1019/cm(3)) were used for the study. We demonstrated the existence of two different degradation mechanisms, depending on the stress conditions: (i) when submitted to TLP stress (100 ns pulses with increasing amplitude), the failure occurs through a field driven process, i.e. the breakdown of the metal/p-GaN Schottky junction, which is reversely biased when the gate is at positive voltage. Failure voltage decreases with increasing Mg doping, since higher acceptor levels result in a higher electric field. (ii) Conversely, during constant-voltage stress, the long-term stability is undermined by a current-driven process, namely the accumulation of positive charges at the p-GaN/AIGaN interface, which promotes an increase of the leakage current, first gradual and then catastrophic. Increasing Mg-concentration in the p-GaN results in a reduction of the gate leakage at high forward gate bias. As a consequence, devices with higher Mg doping have long TTF (more than two orders of magnitude with respect to the samples with lower Mg doping). (C) 2017 The Authors. Published by Elsevier Ltd.