Modelling the gate capacitances of MESFETs and HEMTs from low-frequency C-V measurements

A novel modelling technique is presented to describe the gate capacitance non-linearities of MESFETs and HEMTh. The method is based on a set of low-frequency C-V measurements and new empirical expression for the bias-dependent gate-to-source and gate-to-drain capacitances. Extraction of the model parameters follows a two-step curve-fitting procedure and the method is equally applicable to C-V data extracted from small-signal S-parameter measurements. The model is tested on a number of commercial devices, both MESFETs and HEMT, showing a better agreement with experimental data then previous models. Finally, the model proposed gives a very accurate description of the total gate capacitance at zero drain-to-source voltages and this leads to a simple and fast technique to determine the approximate doping profile of the active channel.