Synthesis of Ultrathin Topological Insulator β-Ag₂ Te and Ag₂ Te/WSe₂ -Based High-Performance Photodetector

β-Ag₂ Te has attracted considerable attention in the application of electronics and optoelectronics due to its narrow bandgap, high mobility, and topological insulator properties. However, it remains a significant challenge to synthesize 2D Ag₂ Te because of the non-layered structure of Ag₂ Te. Herein, the synthesis of large-size, ultrathin single crystal topological insulator 2D Ag₂ Te via the van der Waals epitaxial method for the first time is reported. The 2D Ag₂ Te crystal exhibits p-type conduction behavior with high carrier mobility of 3336 cm² V^-1 s^-1 at room temperature. Taking advantage of the high mobility and perfect electron structure of Ag₂ Te, the Ag₂ Te/WSe₂ heterojunctions are fabricated via mechanical stacking and show an ultrahigh rectification ratio of 2 × 10⁵ . Ag₂ Te/WSe₂ photodetector also exhibits self-driven properties with a fast response speed (40 µs/60 µs) in the near-infrared region. High responsivity (219 mA W^-1 ) and light ON/OFF ratio of 6 × 10⁵ are obtained under the photovoltaic mode. The overall performance of the Ag₂ Te/WSe₂ photodetector is significantly competitive among all reported 2D photodetectors. These results indicate that 2D Ag₂ Te is a promising candidate for future electronic and optoelectronic applications.