Self-consistent simulation of modulation-doped field-effect transistors

Due to the fact that conventional linear charge-control modulation-doped field-effect transistor (MODFET) models assume full depletion in the doping layer, they are not able to model the nonlinear charge-control relation arising from neutralized donor effect near large gate bias. This neutralized donor effect, also called parasitic MESFET effect, saturates two-dimensional electron gas (2DEG) concentration and raises gate-source capacitance to make high frequency performance poor. In this paper, electron behavior of MODFET along the growth direction is numerically modeled through self-consistent calculation to achieve a more exact charge-control relation. Then, 2DEG channel mobility is described by a semi-empirical analytical form and substituted into a current-density equation together with the charge-control relation fitted by least-square polynomial in order to easily solve for drain-source current and gate transconductance. These theoretically calculated results are in good agreement with those experimental results presented in the literature.