Light-induced sidegating effect in GaAs MESFET's

Light sensitivity of the sidegating effect in GaAs MESFETs is investigated by performing two-dimensional numerical simulations on realistic sidegate structures. The mechanism of the light-induced sidegating is identified and compared with alternative mechanisms of sidegating including trap-fill-limited conduction and conduction through the Schottky-i-n(sidegate) structure. Ionization of hole traps in the substrate by the capture of photogenerated holes is found to be the major cause of light-induced sidegating, which occurs even at very low sidegate voltages. In the presence of the occupied hole traps the potential distribution in the electron-trap-rich substrate becomes similar to that in the hole-trap-rich substrate, i.e., the negative voltage applied to the sidegate is carried over to the channel-substrate interface.>