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

Abstract

We conducted reliability characterization under reverse-bias stress (i.e., stress at OFF-state with high ${V}_{\text {DS}}$ ) 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 ( ${V}_{\text {TH}}$ ) stability than that with a grounded substrate. A non monotonic dependence of ${V}_{\text {TH}}$ shifts and OFF-state time-to-breakdown ( ${t}_{\text {BD}}$ ) on the positive substrate bias ( ${V}_{\text {sub}}$ ) was also observed. The underlying mechanisms are the different impacts of positive ${V}_{\text {sub}}$ 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 ${V}_{\text {TH}}$ stability in applications of the GaN MIS-FET.