Schottky barrier depletion modification-a source of output conductance in submicron GaAs MESFETs

This investigation offers a new explanation for the output conductance in submicron GaAs MESFET characteristics. Prior to the avalanche breakdown a sharp rise in the reverse Schottky barrier current, I_gs is observed at a potential where drain-to-source current, I_ds saturates. This could be attributed to the fact that after the onset of current saturation there is an increase in the effective channel height of the device as a function of drain-to-source voltage, V_ds. Experimental data suggest that by increasing V _ds, there are more unbalanced positive ionic charges in the gate depletion toward the drain-side of the Schottky barrier. The electric field lines originated by these uncompensated charges induce an opposite charge density in the gate electrode. This modifies the gate biasing and hence the Schottky barrier depletion. As a result there is a wider available channel crossection for the flow of I_ds(V_ds) and consequently the current-voltage (I-V) characteristics exhibit a positive slope after V_ds saturation