SWITCHING CHARACTERISTICS OF AN OPTICALLY CONTROLLED GAAS-MESFET

The switching characteristics of an optically controlled Metal Semicon ductor Field Effect Transistor (MESFET), popularly known as Optical Fi eld Effect Transistor (OPFET), have been derived analytically. The lim itations of the existing model have been overcome in the present model . Calculations are being carried out to examine the effect of illumina tion on the current-voltage characteristics, drain-to-source capacitan ce (C(dc)), internal gate-to-source capacitance (C(gs)), drain-to-sour ce resistance (R(ds)), the transconductance (g(m)), the input RC time constant and the cutoff frequency (f(T)) of a GaAs-MESFET. The variati ons of these parameters with gate length L(g) and the doping concentra tion N(d) have also been studied in dark and illuminated conditions. T he results of numerical calculations show that there is an overall dec rease in the input RC time constant of the device in the illuminated c ondition arising from the internal gate-to-source capacitance and the transconductance. The results obtained on the basis of the model show a close agreement with the reported experimental findings. The simple model presented here is fairly accurate and can be used as a basic too l for circuit simulation purposes.