On the origin of drain current transients and subthreshold sweep hysteresis in 4H-SiC MOSFETs

In 4H silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs), slow drain current transients and strong sweep hysteresis govern the subthreshold regime, in particular, after negative gate stress. Although these are clearly charge carrier trapping and emission phenomena, a physical model describing the effect to a full extent is missing. In this paper, we investigate a-face n-channel 4H-SiC trench MOSFETs and record drain current transients over seven decades of time for gate voltages below and above threshold. We find clear evidence that the transients result from electron capture rather than from hole emission. Thereby, the time constant for electron capture into interface or near-interfacial defects is broadly distributed and is well characterized by a lognormal distribution. Based on the findings, we propose a physical model that consistently describes the time-dependent measured data in the full gate voltage range. The resulting trap density for the investigated MOSFETs equals 4.2 × 1012 cm–2 with a median electrical capture cross section of 2.5 × 10 − 19 cm2. The distribution of capture time constants has a width of 1.6 orders of magnitude.