Low-threshold exciton transport and control in atomically thin semiconductors

TL;DR

This paper demonstrates a nanoscale device that efficiently confines and controls excitons and trions in 2D semiconductors, achieving higher funneling efficiency and low strain thresholds, advancing nano-excitonic device technology.

Contribution

It introduces a nano-gap device for selective exciton and trion confinement in 2D materials, with dynamic control and improved efficiency over previous methods.

Findings

Exciton funneling efficiency of ~25% achieved.

Low strain threshold (~0.1%) for exciton control.

Dynamic control of exciton and trion rates demonstrated.

Abstract

Understanding and controlling the nanoscale transport of excitonic quasiparticles in atomically thin 2D semiconductors is crucial to produce highly efficient nano-excitonic devices. Here, we present a nano-gap device to selectively confine excitons or trions of 2D transition metal dichalcogenides at the nanoscale, facilitated by the drift-dominant exciton funnelling into the strain-induced local spot. We investigate the spatio-spectral characteristics of the funnelled excitons in a WSe2 monolayer (ML) and converted trions in a MoS2 ML using hyperspectral tip-enhanced photoluminescence (TEPL) imaging with <15 nm spatial resolution. In addition, we dynamically control the exciton funnelling and trion conversion rate by the GPa scale tip pressure engineering. Through a drift-diffusion model, we confirm an exciton funnelling efficiency of ~25 % with a significantly low strain threshold (~0.1 %) which sufficiently exceeds the efficiency of ~3 % in previous studies. This work provides a new strategy to facilitate efficient exciton transport and trion conversion of 2D semiconductor devices.