Gate-voltage dependence of source and drain series resistances and effective gate length in GaAs MESFETs

Experimental data and calculated results are presented to show that the source and drain series resistances in GaAs MESFETs are gate-voltage dependent. This dependence is caused by the gate-voltage modulation of the ungated portions of the channel. A simple analytical model is proposed that accounts for this dependence by introducing an effective gate-voltage-dependent gate length. For nominal 1- mu m gate devices the effective gate length is 0.2-0.3 mu m longer than the metallurgical gate length.>