Van der Waals Epitaxy of Bi₂ Te₂ Se/Bi₂ O₂ Se Vertical Heterojunction for High Performance Photodetector

Bismuth oxyselenide (Bi₂ O₂ Se) has emerged as a promising candidate for electronic and optoelectronic applications due to its outstanding electron mobility and ambient stability. However, high dark current and relatively slow photoresponse that originate from high charge carrier concentration as well as bolometric effect in Bi₂ O₂ Se inhibit further improvement of Bi₂ O₂ Se based photodetectors. Here, a one-step van der Waals (vdW) epitaxy synthesis of Bi₂ Te₂ Se/Bi₂ O₂ Se vertical heterojunction with type-II band alignment and high-quality interface is demonstrated. The crystal quality and uniformity of the heterojunction are supported by Raman, transmission electron microscopy and energy dispersive spectroscopy results. A photodetector based on Bi₂ Te₂ Se/Bi₂ O₂ Se heterojunction demonstrates steady photoresponse over a large wavelength range (532-1456 nm), with a high specific responsivity of 2.21 × 10³ A W^-1 at 532 nm and fast response speed of 50 ms. Moreover, field effect regulation allows for further improvement of the photoresponse performance of the heterojunction field effect transistor device, where the responsivity can be increased to 3.34 × 10³ A W^-1 with a 60 V gate voltage. Overall, the one-step vdW epitaxy process is a promising and convenient route towards constructing high quality Bi₂ O₂ Se based heterojunction for improving its photodetection performance.