Sensitivity of a Hybrid Heterojunction Self-Powered Pentacene Schottky Photodetector

A Schottky hybrid heterojunction photodiode comprising Al/pentacene/p-Si/Pd has been fabricated using thermal vacuum evaporation to deposit pentacene on a p-type silicon substrate. The energy band diagram shows a Schottky contact at the Al/pentacene interface with a significant energy barrier ($\boldsymbol {\Delta }$Ec) and a smaller barrier ($\boldsymbol {\Delta }$Ev) at the pentacene/p-Si junction.$I$–$V$and$C$–$V$measurements were conducted from$\boldsymbol {-}4$to$\boldsymbol {+}4$V at room temperature, both in the dark and under three visible light wavelengths (blue, green, and red). In$I$–$V$mode, the device current increases with exposure to the longer wavelengths, aligning with the absorbance spectrum. The zero-bias sensitivity for red light is 1.04%$\boldsymbol {\times } \,\, 10^{{4}}$%, significantly higher than the forward bias sensitivity of 1.31%$\boldsymbol {\times } \,\, 10^{{2}}$% and 3.5 times greater than the reverse bias sensitivity of 2.9%$\boldsymbol {\times } \,\, 10^{{3}}$%.$C$–$V$measurements were taken at frequencies from 0.1 kHz to 1 MHz, showing typical inversion-depletion-accumulation behavior. The maximum electric field in the depletion layer was 32.3 kV/cm, indicating a well-defined depletion region. Capacitance differences increased with higher energy photons (blue light). To compare and contrast, the maximum current sensitivity in$I$–$V$mode occurred at 0 V, with values of 2.23%$\boldsymbol {\times } \,\, 10^{{2}}$% for blue light and 1.04%$\boldsymbol {\times } \,\, 10^{{4}}$% for red light. While in$C$–$V$mode, maximum capacitive sensitivity was at −0.6 V, with blue light sensitivity at 60% and red light sensitivity at 40%. This device is recommended for use as a self-powered photovoltaic mode visible light sensor.