Investigating the Arc-Shaped Kink Drain Voltage of Drain Current With Capacitance-Voltage Measurement Method in GaN HEMTs

In this study, the measure-stress-measure (MSM) technique under the arc-shaped kink drain voltage (VD,kink) conditions is applied to investigate the ${\mathrm { V}}_{\mathrm { D,kink}}$ in GaN high electron mobility transistors (HEMTs). Forward and reverse transfer curves indicate that the ${\mathrm { V}}_{\mathrm { D,kink}}$ would change with gate voltages increasing. However, no previous study has investigated the exact location of traps that would dominate the loci of VD,kink. The results suggest that the trend of on-state current (Ion) degradation is caused by threshold voltage (Vt) shift. Hence, it can be determined that the ${\mathrm { V}}_{\mathrm { D,kink}}$ is related to the degree of impact ionization, which is dominant by the holes generation in the buffer. In addition, the capacitance-voltage (C-V) measurements reveal that holes generated through impact ionization at the gate edge are responsible for the shift in VD,kink. This physical mechanism is further supported by temperature-dependent analysis. Finally, the results offer a novel C-V measurement to characterize and model the physical mechanisms of the kink effect, which is governed by hot carrier degradation in GaN HEMTs.