Electroluminescence Dynamics across Grain Boundary Regions of Monolayer Tungsten Disulfide.

We study how grain boundaries (GB) in chemical vapor deposition (CVD) grown monolayer WS2 influence the electroluminescence (EL) behavior in lateral source-drain devices under bias. Real time imaging of the WS2 EL shows arcing between the electrodes when probing across a GB, which then localizes at the GB region as it erodes under high bias conditions. In contrast, single crystal WS2 domains showed no signs of arcing or localized EL. Analysis of the eroded GB region shows the formation of micro- and nanoribbons across the monolayer WS2 domains. Comparison of the EL spectrum with the photoluminescence spectrum from the monolayer WS2 shows close agreement, indicating the EL emission comes from direct band gap excitonic recombination. These results provide important insights into EL devices that utilize CVD grown monolayer transition metal dichalcogenides when GBs are present in the active device region.