On the subthreshold drain current sweep hysteresis of 4H-SiC nMOSFETs

We study the subthreshold drain current hysteresis of 4H silicon carbide Si-face (0001) and a-face (1120) n-channel power MOSFETs between gate voltage sweeps from accumulation to inversion and vice versa. Depending on the direction of the gate voltage sweep, the MOSFETs show a different subthreshold drain current at the same gate voltage. The observed hysteresis between up-sweep and down-sweep can be expressed as a subthreshold voltage shift and may reach several volts. We show that the voltage shift is caused by hole capture in border traps during accumulation and is directly propotional to the charge pumping signal. The voltage shift is fully recoverable by applying a gate bias above the threshold voltage and does not impact device reliability.