Transferrable van der Waals Epitaxy of AlN on h-BN for Flexible Vacuum Ultraviolet Photodetection

van der Waals epitaxy (vdWE) of three-dimensional (3D) semiconductor films on two-dimensional (2D) materials has emerged as a cutting-edge platform for advanced heterostructures. In this work, we systematically investigate the interfacial bonding mechanism of AlN on h‑BN and demonstrate high-performance flexible vacuum-ultraviolet photodetectors (VUV PDs) based on the epitaxial AlN film. Oxygen dangling bonds introduced by O2 plasma pretreatment effectively promote the nucleation of AlN. By precisely regulating the nucleation density, we achieve a smooth, high-crystallinity, and transferrable AlN film on the h‑BN buffer layer. The resulting freestanding AlN membrane obtained via mechanical exfoliation serves as the active layer in flexible VUV PDs that operate in a self-driven mode, exhibiting a responsivity of 0.24 mA/W at 0 V bias. Under an applied bias of -20 V, the device delivers a high on/off ratio of 2.4×104 and excellent reproducibility. This work provides a key strategy for achieving high-quality flexible III-nitride films, paving the way for the flexible high-performance VUV optoelectronic devices.