A Study of the Gate-Stack Small-Signal Model and Determination of Interface Traps in GaN-Based MIS-HEMTs

The existing gate-stack small-signal models of metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were analyzed, and a new model that could fit the measured admittance characteristics in the whole bias regime after learning about their shortcomings was presented. The capacitance and conductance frequency characteristics were fitted simultaneously, and the extracted fitting parameters showed reasonable values and trends. These parameters were then used in the determination of interface traps as well as the quantitative analysis of two C-V slopes for MIS-HEMTs. It was proven that the intrinsic barrier resistance was also a critical factor for the second slope. Thus, this resistance could not be neglected by the capacitance method that determined the interface trap densities directly by the frequency dispersion of the second slope. This article extracted the energy distribution of the interface trap density, which could be fitted by a Gaussian distribution with a maximum value of ~ 3×10
¹²
cm
^-2
eV
^-1
. Although this method was a suitable alternative because the capacitance and conductance were correlated by the admittance characteristics, the detected shallow-level traps may not account for the threshold voltage drift or other reliability problems of MIS-HEMTs.