WSe ₂ pn Homojunction Photodetector Engineered by In Situ Ferroelectric Doping

Abstract 2D transition metal dichalcogenides (TMDs) exhibit remarkable electronic and optoelectronic properties. Optoelectronic pn junctions based on TMDs have achieved exceptional performance, demonstrating outstanding versatility and multifunctionality. However, current fabrication of 2D photovoltaic devices is still hindered by several challenges. The transferring process in creating heterojunctions introduces contamination and interface defects, resulting in carrier mobility degradation and declining device performance. Additionally, doping techniques used to form homojunctions face difficulties such as doping misalignment, instability, and disruption of the lattice structure. In this work, the ferroelectric effect of periodically poled lithium niobate is leveraged to achieve in situ doping and fabricate a high‐quality, precisely‐positioned, non‐destructive WSe ₂ pn homojunction photodetector. The surface potential, carrier type and density of WSe ₂ are engineered in a nonvolatile way by the ferroelectric field of PPLN, which are characterized and confirmed through Kelvin Probe Force Microscopy, PL spectroscopy, and Raman scattering spectroscopy. The WSe ₂ pn homojunction, modulated via PPLN, demonstrates distinct rectification properties. It presents a large on–off ratio of 6.8 × 10 ³ and a responsivity of 0.36 A W ⁻¹ at the wavelength of 450 nm, all achieved under zero bias conditions. This approach enables us to fabricate homojunction self‐powered photodetectors, thereby paving the way for the development of 2D devices.