OFF-state breakdown and threshold voltage stability of vertical GaN-on-Si trench MOSFETs

In this paper we analyze the OFF-state performance of vertical GaN-on-Si Trench MOSFETs in terms of breakdown voltage and stability of the threshold voltage. We proved that the devices fail in OFF-state due to the breakdown of the unprotected gate oxide. Then, by means of a series of fast V TH transient experiments, we demonstrate that the OFF-state threshold voltage instability is given by the trapping of electrons at deep levels in the p-GaN body layer, transported by the rather high drain current leakage. The interpretation was supported by deep level spectroscopy measurements, carried out on p-n junctions located on the same wafer. • The breakdown in OFF-state regime of vertical GaN trench MOSFETs was investigated by means of stepstress experiments. • The failure of the devices is associated with an excess of electric field in the gate oxide layer. • We detected a V TH instability mechanisms during an OFF-state stress, associated to the vertical electric field or leakage. • V TH instability due to trapping of electrons in deep levels within the semiconductor layers.