Two-dimensional charge-control model for MODFET's

A dc model for MODFET's accounting for two-dimensional effects is proposed. In this model, charge control is realized by solving the two-dimensional Poisson equation in the depleted AlGaAs region. The transport picture used for the two-dimensional electron gas (2-DEG) in the AlGaAs/GaAs heterojunction relies on the quasi-Fermi level together with a field-dependent mobility and therefore includes 2-DEG diffusion effects. Our approach reduces the analysis to a single integral equation.
I-V
curves, which provide a good fitting to the reported experimental data, are obtained using a smooth velocity-field curve. The channel voltage, 2-DEG concentration, parallel electric-field, and drift velocity along the channel are given in this study and provide a clear picture of current saturation. The model is consistent with the approximate two-region saturation picture but provides a smoother transition. We observe a large diffusion current component along the channel in addition to the drift current. However, the total saturation current obtained has nearly the same value as found from the two-region model. This new model with two-dimensional charge control provides much insight into the current saturation mechanism of the MODFET.