Physics of dynamic threshold voltage and steep subthreshold swing in Al₂O₃–InAlN–GaN MOSHEMTs

The impact of Al₂O₃–InAlN interface traps on the switching characteristics of Al₂O₃–InAlN–GaN MOSHEMTs was examined using temperature-dependent current–voltage characterization. A steep subthreshold swing (SS) as low as 37 mV/dec at 25 °C is obtained, and shows negative temperature dependence up to 180 °C. We attribute this behavior to the dynamic threshold voltage (V _th) induced by the de-trapping of the acceptor-like interface traps near the InAlN conduction-band edge, which acts as a positive feedback in increasing the drain current during the switch-on process. At elevated temperature, the thermally activated de-trapping of the deeper traps results in a more sufficient dynamic shift in V _th and then leads to a steeper SS. The traps contributing to the steep SS were found within the energy levels ranging from E _C − 0.55 to E _C − 0.833 eV for the measured temperature range (25–180 °C). On the other hand, the interface traps near the midgap or at deeper energy levels act as quasi-fixed charges, which feature negligible impact on the switching behavior of the device. (paper)