Hole-Induced Degradation in ${E}$ -Mode GaN MIS-FETs: Impact of Substrate Terminations

We conducted reliability characterization under reverse-bias stress (i.e., stress at OFF-state with high VDS) on the E-mode GaN metal-insulator-semiconductor field-effect-transistors (MIS-FETs) with various substrate terminations. The MIS-FETs with floating substrate (FS) show worse threshold voltage (VTH) stability than that with a grounded substrate. A non monotonic dependence of VTH shifts and OFF-state time-to-breakdown (tBD) on the positive substrate bias (Vsub) was also observed. The underlying mechanisms are the different impacts of positive Vsub on the drift of electrons and holes during the long-term stress. An important indication is that positive-biased and FS terminations should be restricted at OFF-state in order to obtain good VTH stability in applications of the GaN MIS-FET.