Atomically thin lateral p-n junction photodetector with large effective detection area

The widely used photodetector design based on atomically thin transition metal dichalcogenides (TMDs) has a lateral metal-TMD-metal junction with a fairly small, line shape photoresponsive active area at the TMD-electrode interface. Here, we report a highly efficient photodetector with extremely large photoresponsive active area based on a lateral junction of monolayer-bilayer WSe₂. Impressively, the separation of the electron-hole pairs (excitons) extends onto the whole 1L-2L WSe₂ junction surface. The responsivity of the WSe₂ junction photodetector is over 3200 times higher than that of a monolayer WSe₂ device and leads to a highest external quantum efficiency of 256% due to the efficient carrier extraction. Unlike the TMDp-n junctions modulated by dual gates or localized doping, which require complex fabrication procedures, our study establishes a simple, controllable, and scalable method to improve the photodetection performance by maximizing the active area for current generation.