Optoelectronic devices based on electrically tunable p–n diodes in a monolayer dichalcogenide

The p–n junction is the functional element of many electronic and optoelectronic devices, including diodes, bipolar transistors, photodetectors, light-emitting diodes and solar cells. In conventional p–n junctions, the adjacent p- and n-type regions of a semiconductor are formed by chemical doping. Ambipolar semiconductors, such as carbon nanotubes 1 , nanowires 2 and organic molecules 3 , allow for p–n junctions to be configured and modified by electrostatic gating. This electrical control enables a single device to have multiple functionalities. Here, we report ambipolar monolayer WSe 2 devices in which two local gates are used to define a p–n junction within the WSe 2 sheet. With these electrically tunable p–n junctions, we demonstrate both p–n and n–p diodes with ideality factors better than 2. Under optical excitation, the diodes demonstrate a photodetection responsivity of 210 mA W –1 and photovoltaic power generation with a peak external quantum efficiency of 0.2%, promising values for a nearly transparent monolayer material in a lateral device geometry. Finally, we demonstrate a light-emitting diode based on monolayer WSe 2 . These devices provide a building block for ultrathin, flexible and nearly transparent optoelectronic and electronic applications based on ambipolar dichalcogenide materials. An electrostatically defined p–n junction in monolayer WSe 2 is employed for photodetection, photovoltaic operation and as a light-emitting diode.