SURFACE SENSITIVITY AND BIAS DEPENDENCE OF NARROW-GAP METAL-SEMICONDUCTOR-METAL PHOTODETECTORS

The electrical field distribution in a Schottky contact metal-semiconductor-metal (MSM) photodetector is one-dimensionally approximated and applied to the solution of the illuminated dc characteristics using a bipolar transport model. A solution is produced that is valid for an arbitrary distribution of the incident optical intensity and all ranges of the applied bias voltage. It is shown that the observed dependence of the response on the illumination distribution and the saturation of the photocurrent with increasing applied bias are both determined by the efficiency of the internal field distribution in separating and collecting the generated electron-hole pairs. This description agrees with experimental measurements of Schottky contact MSM photodetectors fabricated on semi-insulating GaAs.