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 degrees C is obtained, and shows negative temperature dependence up to 180 degrees 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 degrees 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.