Device Modeling for Admittance Spectroscopy of PMOSFETs at Cryogenic Temperatures

Large area PMOSFETs were characterized at room and cryogenic temperatures by admittance spectroscopy to determine transport parameters (e.g., hole mobility in the inversion layer). The devices were simulated in the linear response regime by an efficient drift-diffusion (DD) model including Fermi-Dirac statistics, band tailing and impurity freezeout that shows excellent numerical stability under cryogenic conditions. By inverse modeling accurate device models of the complex PMOSFETs were derived avoiding the stringent approximations of the analytical approaches. A high degree of consistency of simulations and measurements for the small-signal capacitance, conductance and drain current was obtained, by which the hole mobility extracted from the drain current could be verified by independent conductance measurements. In a next step the model could be used to extract data of interface states from measurements at 4.2 K, for which the usual methods based on MOS capacitors fail due to impurity freezeout.