Differential Responsivity of the Organic-Inorganic Ag/n-GaAs/p-CuPc/Ag Photoelectric Sensor

Abstract

A thin film of copper phthalocynanine (CuPc) as p‐type semiconductor was deposited by vacuum evaporation on an n‐type GaAs single‐crystal semiconductor substrate. Then semitransparent Ag thin film having gradient of thickness was deposited on CuPc film by thermal evaporation in vacuum to fabricate Ag/n‐GaAs/p‐CuPc/Ag sensor. Due to gradient of thickness, 6% and 10% of the incident light can be transmitted through the silver film in the edge and in the center of the sample respectively. Open circuit voltage and short circuit current were measured by exposing only a small area of the sensor to light i.e. in differential mode of operation. It was observed that open‐circuit voltage and short‐circuit current depends on position of the exposed area of the sensor to light. In differential mode of operation the open‐circuit voltage and short circuit current versus intensity of illumination showed less non linearity as compared to integral mode of operation. On the basis of experimental data, an equivalent circuit of the sensor was designed and its computer simulation was carried out. The simulated data matched reasonably with the experimental curves. It was found that in differential mode of operation the Ag/n‐GaAs/p‐CuPc/Ag sensor's output voltage and current depends on the position of light beam probe. Due to this the sensor may be used as a photoelectric displacement transducer.