A Monolayer Semiconductor Free-Space Electro-Optical Modulator

Two-dimensional (2D) semiconductors are promising building blocks for future electronic and optoelectronic devices. At cryogenic temperatures, their strong exciton resonances can facilitate near-unity modulation of light beams, suggesting a tantalizing opportunity to create atomically thin elements for dynamic light-field control. However, it remains challenging to achieve efficient modulation with 2D semiconductors at room temperature as the ratios between their intrinsic radiative decay rates and the non-radiative decay and dephasing rates notably reduce with increasing temperature. Here, we demonstrate a monolayer tungsten disulfide (WS₂) free-space electro-optical modulator that offers 3 dB signal modulation (10% percentage points) at room temperature. This is achieved by leveraging the Purcell effect of a patterned silver gate electrode that supports an optical cavity mode being able to significantly boost the local density of states of light. The patterned electrode is further integrated into a compact metal-oxide-semiconductor capacitor configuration that facilitates low-power, solid-state electrical tuning of the excitonic resonance. We also illustrate how dynamic control of light fields can be achieved with designer surface patterns.