Low field mobility, effective saturation velocity and performance of submicron GaAs MESFETs

An analytical model is proposed which relates the transconductance of submicron GaAs MESFETs to a low field mobility, effective electron saturation velocity and device geometry and doping. The model predicts that the effective saturation velocity determines the performance of the devices at relatively high pinch-off voltages (Vpo > 5 V). At smaller pinch-off voltages (especially for enhancement-mode devices) the low field mobility becomes increasingly important, leading to additional advantages of GaAs devices over Si devices. Another prediction is a higher transconductance in thinner and higher-doped devices. This effect is also more important for devices with low pinch-off voltages. The obtained results may be used to deduce the effective values of the electron drift velocity in GaAs MESFETs as a function of the gate length.