Substrate current in GaAs MESFET's

It is shown that the substrate current in GaAs MESFET's may be related to the electron injection into the substrate region adjacent to the high-field domain in the active layer. A simple one-dimensional calculation shows that the substrate current Isubis proportional toVmin{ds}max{1/2}andnmin{0}max{1/4}where Vdsis the drain-to-source voltage, n0is the doping density in the active layer. Atn₀ = 10¹⁷cm-3andVds 10V we estimateI_{} ~ 50mA per millimeter gate in good agreement with experimental results.