Homogeneous in-plane WSe 2 P-N junctions for advanced optoelectronic devices.

Conventional doping schemes of silicon (Si) microelectronics are incompatible with atomically thick two-dimensional (2D) transition metal dichalcogenides (TMDCs), which makes it challenging to construct high-quality 2D homogeneous p-n junctions. Herein, we adopt a simple yet effective plasma-treated doping method to seamlessly construct a lateral 2D WSe 2 p-n homojunction. WSe 2 with ambipolar transport properties was exposed to O 2 plasma to form WO x on the surface in a self-limiting process that induces hole doping in the underlying WSe 2 via electron transfer. Different electrical behaviors were observed between the as-exfoliated (ambipolar) region and the O 2 plasma-treated (p-doped) region under electrostatic modulation of the back-gate bias ( V BG ), which produces a p-n in-plane homojunction. More importantly, a small contact resistance of 710 Ω μm with a p-doped region transistor mobility of ∼157 cm 2 V -1 s -1 was achieved due to the transformation of Schottky contact into Ohmic contact after plasma treatment. This effectively avoids Fermi-level pinning and significantly improves the performance of photodetectors. The resultant WSe 2 p-n junction device thus exhibits a high photoresponsivity of ∼7.1 × 10 4 mA W -1 and a superior external quantum efficiency of ∼228%. Also, the physical mechanism of charge transfer in the WSe 2 p-n homojunction was analyzed. Our proposed strategy offers a powerful route to realize low contact resistance and high photoresponsivity in 2D TMDC-based optoelectronic devices, paving the way for next-generation atomic-thickness optoelectronics.