Analytic modeling of nonlinear current conduction in access regions of III-Nitride HEMTs

The transconductance degradation caused by the non-linear resistance of access regions in III-nitride high electron-mobility transistors (HEMTs) is mainly responsible for limiting the RF linearity of the transistor. In this paper, we use Landauer's transmission theory to develop an analytic electrothermal current-voltage (I-V) model of access regions in III-nitride HEMTs. With only 12 parameters, most of which have a physical origin and can be obtained through experimental calibration, the model is able to correctly predict the I-V behavior in access regions from the drift-diffusive to the quasi-ballistic transport regimes. Model accuracy is demonstrated by comparing the results against experimental and numerical hydrodynamic simulations of ungated transmission line structures with length scales ranging from few 10's of nanometers to 10's of micrometers.