Optically-controlled switching characteristics of silicon MESFETs

The switching time of a silicon MESFET device can be controlled by photons incident on the transparent or semitransparent gate, which may be treated as the virtual gate in addition to usual gate. Studies have been made on the optically-controlled switching characteristics of the Silicon MESFET which show that the internal gate-source capacitance increases with increasing radiation flux density under normally OFF conditions and decreases under normally ON conditions. Further, the drain-to-source resistance is found to be reduced with increasing radiation flux density at a particular value of absorption coefficient (or wavelength of radiation). The effect of radiation becomes predominant over the impurity concentration at flux-density ≥ 10¹⁸/m². Also it is observed that RC time constant decreases initially with increasing radiation up to 10¹⁸/m². At a radiation intensity equal to 10¹⁹/m², the RC time constant gradually decreases with increased doping level.