A new technique for characterization of the "End" resistance in modulation-doped FET\´s

We propose a new extended "end" resistance measurement technique to determine the series source and drain resistance of a field-effect transistor. In this method the small-signal "end" resistance, defined as a derivative of the drain-source voltage, with respect to the gate current, is measured as a function of the drain current. The "end" resistance includes the contributions from the source series resistance and from the resistance related to the conducting channel under the gate. As the drain current increases, the drain side of the channel becomes more reverse biased with respect to the gate. This shifts the gate current distribution towards the source, decreasing the channel contribution to the "end" resistance. By extrapolation to infinite drain current the channel contribution can be eliminated and the series resistance of the undepleted source and drain regions can be accurately determined. The technique is applied to a long-gate modulation-doped field-effect transistor and is shown to Yield reasonable values of the series resistances.