Electroluminescence of monolayer WS2 in a scanning tunneling microscope: Effect of bias polarity on spectral and angular distribution of emitted light

Abstract

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Tip-Induced and Electrical Control of the Photoluminescence Yield of Monolayer WS2

“…18,27 In all of the reported experiments, where the PL is detected with the STM tip engaged, the STM-induced electroluminescence (STML) of the sample 28 is undetected or negligible as compared to the detected PL signal. In particular, the STM-induced effects reported in this letter are observed regardless of whether the bias voltage applied to the tip−sample junction is lower or higher than the STML onset voltage for this sample (V s ≈ 1.8 V), 29 which confirms that these effects are not due to STML (more data is available in Section S7 in the Supporting Information).…”

“…38 Recent publications on monolayer WS 2 on ITO suggest that it is n-doped. 29,39 Electron injection via tunneling from the tip into the conduction band of the n-doped semiconductor will locally increase the density of majority charge carriers, whereas the inverse effect may be obtained if electrons tunnel from the sample to the tip. Thus, if higher charge carrier densities in the semiconductor yield stronger PL quenching, we expect a stronger quenching effect at positive as compared to negative sample bias.…”

Overbias Photon Emission from Light-Emitting Devices Based on Monolayer Transition Metal Dichalcogenides

“…However, there are also alternative ways to generate excitons for light emission such as by energy transfer. This process involves inelastic electron tunneling (IET), in which the electron couples its energy to TMD excitons during the tunneling process. − Such energy transfer can occur efficiently in van der Waals (vdW) heterostructures and is due to strong near-field coupling between the tunneling electrons and the active material. Thus, excitons in TMDs can be generated either by charge injection or by energy transfer.…”