High-performance, Self-powered ZnO NWs-ZnSe Heterojunction Photodetectors for Superior Visible and Near-Infrared Detection

We present the development of a type-II heterojunction photodetector comprising Ag/ZnO nanowires (NWs)/ZnSe/In, fabricated on a commercially available Si substrate. ZnO NWs were hydrothermally synthesized on thermally evaporated ZnSe thin films, with SEM analysis revealing uniform, vertically aligned ZnO NWs on the ZnSe layer. Cross-sectional SEM imaging determined the thickness of the In/ZnSe thin film to be approximately 460 nm, with ZnO NWs exhibiting an average diameter of ~161 nm. Structural analysis of the ZnSe thin film, annealed at 370°C in an ambient environment, identified a prominent ZnSe peak at 27.48° alongside peaks at 30.98° and 33.21° corresponding to In2O3 and ZnSeO3, respectively. The ZnO NWs, under similar annealing conditions, displayed a strong (002) peak, confirming vertical growth. Hall effect measurements revealed a transition from p-type carriers in as-deposited ZnSe thin films to n-type in the annealed ZnSe and ZnO NWs, attributed to the formation of In2O3 as evidenced by XRD. The photodetector exhibited the highest photoresponse under IR illumination (950 nm), surpassing responses to green (515 nm) and blue (456 nm) LEDs, with a short-circuit current (Isc) of -26 μA and an open-circuit voltage (Voc) of +80 mV, characteristic of a self-powered device. In contrast, minimal photoresponse was observed in a Schottky-type Ag/ZnSe/In junction on the Si substrate. The photoresponse mechanism was elucidated using an energy band diagram, while Density Functional Theory (DFT) simulations using VASP provided a strong correlation with the experimental data, validating the structural and electronic properties of the heterojunction.