Bipolar photoresponse in a BaTiO₃/ZnO heterojunction photodetector for precise light-wavelength discrimination

Bipolar photoresponse photodetectors enable spectral discrimination and optical logic, but conventional devices often suffer from poor stability and complex fabrication. Here, we report a fully solid-state, chip-scale BaTiO₃/ZnO heterojunction photodetector with a simple structure, compact size, and precise wavelength discrimination. Under self-powered operation, it selectively detects 330 nm and 395 nm light with positive and negative photocurrents, showing responsivities of 6.7 and -26.1 mA/W, respectively. Fast response and narrow wavelength selectivity (∼67 nm) are achieved via optimized pyroelectric current regulation. The interplay between the photovoltaic effect in the heterojunction and the polarization of the BaTiO₃ is investigated. Finally, a 5 × 5 BaTiO₃/ZnO array was further demonstrated for encrypted imaging. This work presents a compact, high-performance platform for precise light-wavelength discrimination, optical logic, and secure optical communication.