Abstract:
As symmetrical data characteristics I (V) of the Metal-Semiconductor-Metal (MSM) photodetector, we
wondered how this device can be used as a photoswitch as well as the low temperature on GaAs
photoconductive generally used for this purpose. The impulse response of interdigitated metalsemiconductor- metal photoswich fabricated on GaAs non-intentional doped (NID) absorbing layer is
investigated. The impulse response of GaAs MSM photoswitch for different bias voltage and optical power
and gap between fingers, for λ=780nm was studied experimentally. The pulse shape of the impulse
response is similar, it achieves maximum after fast rise time due to fast electron drift velocity, flowed by
fairly fast decay corresponding to the fast escape of electrons and holes to the interdigitated contacts,
small Schottky contact spacing permitting rapid carrier extraction after photoexcitation, however, it
followed by long tail. High electric field reaches a threshold level, the mobility of electrons decrease as the
electric field is increased, due to the screening of internal field; thereby producing negative resistance
(NDR). The trapping effect is another feasible way to reduce the carrier transit time. It is advantageous to
use thin active layers to reduce the transient response.
