Design calculations for submicron gate-length AlGaAs/GaAs modulation-doped FET structures using carrier saturation velocity/charge-control model

dc and small-signal ac characteristics of AlGaAs/GaAs modulation-doped FET's have been calculated by combining the conventional charge-control model with the carrier velocity saturation concept in realistic submicron gate structures. For the desired threshold voltage and the maximum gate voltage swing, the designer basically selects the thickness of the n-AlGaAs layer, for the preferred doping concentration, from the design graphs provided. Representative theoretical I/V characteristics and saturation current and transconductance versus gate voltage graphs are presented for the 0.25 μm and 0.8 μm gate-length structures with and without the presence of source and drain series resistances.