Measuring the edge recombination velocity of monolayer semiconductors

Understanding\nedge effects and quantifying their impact on the\ncarrier properties of two-dimensional (2D) semiconductors is an essential\nstep toward utilizing this material for high performance electronic\nand optoelectronic devices. WS<sub>2</sub> monolayers patterned into\ndisks of varying diameters are used to experimentally explore the\ninfluence of edges on the material’s optical properties. Carrier\nlifetime measurements show a decrease in the effective lifetime, τ<sub>effective</sub>, as a function of decreasing diameter, suggesting\nthat the edges are active sites for carrier recombination. Accordingly,\nwe introduce a metric called edge recombination velocity (ERV) to\ncharacterize the impact of 2D material edges on nonradiative carrier\nrecombination. The unpassivated WS<sub>2</sub> monolayer disks yield\nan ERV ∼ 4 × 10<sup>4</sup> cm/s. This work quantifies\nthe nonradiative recombination edge effects in monolayer semiconductors,\nwhile simultaneously establishing a practical characterization approach\nthat can be used to experimentally explore edge passivation methods\nfor 2D materials.