Photovoltaic gate biasing edge effect in GaAs MESFETs

A new effect in planar GaAs MESFETs, whereby a sharp increase in optical gain at the transistor edges occurs, is reported for the first time. This gain effect only appears when a large resistor is inserted in series with the gate, to produce the conditions for photovoltaic gate biasing. The mechanism for increased gain at the edges is suggested to be due to carrier photogeneration in the substrate that is subsequently collected by the gate. Application in the area of X-Y addressable transistor array imagers is proposed.