Cavity-interface engineering of spatially programmable exciton-trion populations in monolayer WS2.

Spatially tuned and reconfigurable optical emission in hetero-interfaces of two-dimensional materials remains attractive for opto-electronic and photonic applications. Here, we demonstrate a method to investigate multiple hetero-interfaces in a WS2 monolayer fabricated in a single sample, spatially engineering the exciton and trion populations. We fabricate WS2/HfO2/metal/SiO2/Si interfaces with metals such as Au, Ni, Mo, and Pt, patterned in a WS2 monolayer, where the HfO2/SiO2/Si stack creates parallel-plate reflectors and traps light, forming a Fabry-Pérot-type cavity. This yields a higher trion-to-exciton ratio of 1.34 in WS2/HfO2/SiO2/Si also exhibiting the highest absorption, emission and free carrier density (∼3.97 × 1012 cm-2). The WS2/HfO2/metal/SiO2/Si interfaces exhibit optical reflectance and partially trap the light resulting in different population ratios. In contrast, interfaces without the HfO2 buffer exhibit charge transfer, yielding the lowest trion spectral weight. We demonstrate a unified approach for understanding cavity-interface coupled optical emissions for the fabrication of spatially programmable optoelectronic devices.