High photo-responsivity Au/polyvinyl alcohol (PVA)+di[1-(2-ethoxyethyl)-5-nitrobenzimidazole] copper dichloride/n-Si UV photodiode

Abstract Au/n-Si metal/semiconductor (MS) type diode was transformed into a metal/polymer/semiconductor (MPS) type diode by polyvinyl alcohol (PVA)+benzimidazole Cu complex interfacial layer to achieve better photodiode properties. Au/PVA + benzimidazole Cu complex/n-Si MPS diode's electronic and photo-responsivity (PR) properties were investigated by current-voltage (I-V) measurements under various ultraviolet (UV) (365 nm wavelength) illumination intensities (from 50 to 250 mW/cm2) and at room temperature. It was found that the difference between the dark and high UV illumination I(V) plots of the MPS diode exceeds 105 times. Thus, this higher response to UV illumination has caused the reverse region current of the diode exceeds the forward region current since the first UV illumination level (50 mW/cm2). This ensures both the MPS diode has a very high PR value and allows that the diode working direction can be adjusted with UV exposure. The remarkably high PR values were obtained for P = 100 mW/cm2 as 11.0 A/W at -4.84 V, and 2.14 mA/W at 0 V. Also, main electronic parameters of the MPS diode were calculated by thermionic emission, Ohm law, Cheung&Cheung and Card&Rhoderick methods. The series resistance (Rs) values calculated for each Cheung&Cheung function are compatible each other and there is an acceptable coherence with obtained values by ohmic approach. For the surface states density (Nss) of the MPS diode obtained for each UV illumination, it was found that they are higher than the dark ones and they shifted to lower energy region.