A simple model for determining effects of negative differential mobility and magnitude of saturated velocity on the performance of Schottky-barrier field effect transistors

Abstract

The effects of nonuniform fields in the channel of GaAs MESFETs, and the resulting range of velocities with which carriers drift, are here considered using a simple model in order to determine the effects of negative differential mobility and saturated velocity on the performance of these devices, and of devices made of other materials. On the basis of the equilibrated velocity-field ν( E) characteristic for GaAs, carriers in short-channel FETs drift over much of the source to drain length with the saturated high field velocity, i.e. a velocity about half that used in most previous analytical solutions for GaAs FETs, and one about equal to the maximum carrier velocity in Si. Neglecting transient effects in electron transport, fields at which a negative differential mobility occurs exist over only a very small portion of the channel. The value of low field mobility of the MESFET material is therefore important primarily in determining source resistance.