Characteristics of ZnO-based MSM photodetectors with ZnO cap layer on flexible substrates

In this work, both of ZnO based metal-semiconductor-metal photodetectors with and without ZnO cap layer were fabricated on flexible substrates (polyethylene terephthalate, PET) for comparative analysis. The ZnO films were prepared by a low temperature sputtering process. The photodetector with ZnO cap layer (stack structure: ZnO/Ag/ZnO/PET) shows a much higher UV-to-visible rejection ratio of 1.56×10³ than one without. It can be attributed to the photocurrents significantly enhanced under UV light illumination in such a novel structure. With an incident wavelength of 370 nm and 3 V applied bias, the responsivities of both photodetectors with and without ZnO cap layer are 3.80×10^-2 and 2.36×10^-3 A/W, respectively, which correspond to quantum efficiencies of 1.13 % and 0.07 %. The Schottky barrier height on Ag/ZnO interfaces is also obtained to be 0.782 eV.