Large‐Area Self‐Assembled Hexagonal Boron Nitride Nanosheet Films for Ultralow Dark Current Vacuum‐Ultraviolet Photodetectors

Hexagonal boron nitride (hBN) is one of the most promising candidates for vacuum‐ultraviolet photodetectors (VUV PDs). However, the efficient and low‐cost fabrication of large‐area hBN‐PDs still encounters challenges. Herein, a cost‐effective route is proposed for fast and scalable fabrication of high‐performance VUV PDs via hBN nanosheet (BNNS) films. BNNSs are peeled from bulk hBN and self‐assembled into large‐area ordered films. In such PDs, junction barriers are present at the contact interfaces of BNNSs and give the PDs a “light‐induced reduction of junction barrier height” working mechanism. The number of junction barriers are qualitatively adjusted by designing the size of BNNSs to optimize the performance of the devices. The performance of ultralow dark current (0.27 pA@80 V), high detectivity (3.42 × 1011 Jones), and fast response speed (20.97/17.69 ms) for 185 nm VUV light is achieved by a fabricated PD. Analysis based on the Schottky contact model proves that the large photoresponse is mainly attributed to the reduction of the barriers and series resistance on illumination. Meanwhile, a physical model is established to describe the working process of such PDs, of which conductivity is dominated by the junction barriers. Besides, a flexible PD is also fabricated, depicting excellent stability, and robustness. A cost‐effective route of combining liquid phase exfoliation and self‐assembly technology is proposed for the preparation of large‐scale hBN nanosheet films, further, to fabricate vacuum ultraviolet photodetectors with ultralow dark current, high detectivity, and fast response speed. The working mechanism and electron transport model of these photodetectors are clearly analyzed.