In‐Plane Field‐Driven Excitonic Electro‐Optic Modulation in Monolayer Semiconductor

Abstract 2D semiconductors are attractive candidates for on‐chip electro‐optic modulators due to their ease of integration and rich exciton‐mediated phenomena. While electrostatic doping and out‐of‐plane field effect have been extensively studied, in‐plane field‐induced phenomena remain largely unexplored. Here electro‐optic response of monolayer WSe 2 subject to modulating in‐plane electric fields probed by electroabsorption and electroreflectance spectroscopy is reported. The devices are found to exhibit spatially varying response near exciton resonance, which cannot be explained by predicted effects such as Pockels and excitonic Stark effect. It is shown that the modulation signal is dominated by exciton linewidth broadening and narrowing associated with local accumulation and depletion of free holes. The field and frequency dependence of the devices is distinct from those of charge modulation devices. The observed behavior is ascribed to elastic scattering of excitons with field‐driven intrinsic free carriers.