Limits of funneling efficiency in non-uniformly strained 2D semiconductors

TL;DR

This paper investigates the maximum efficiency of exciton funneling in strained 2D semiconductors, revealing low efficiency in monolayers but higher in heterostructures, with Auger recombination as a limiting factor.

Contribution

It provides a detailed analysis of the physical limits of exciton funneling efficiency in realistic device geometries of 2D semiconductors.

Findings

Funneling efficiency in monolayer TMDCs is less than 5% at all temperatures.

Heterostructures with long exciton lifetimes can reach about 50% efficiency at room temperature.

Auger recombination significantly limits funneling efficiency under intense illumination.

Abstract

Photoexcited electron-hole pairs (excitons) in transition metal dichalcogenides (TMDC) experience an effective force when these materials are non-uniformly strained. In the case of strain produced by a sharp tip pressing at the center of a suspended TMDC membrane, the excitons are transported to the point of the highest strain at the center of the membrane. This effect, exciton funneling, can be used to increase photoconversion efficiency in TMDC, to explore exciton transport, and to study correlated states of excitons arising at their high densities. Here, we analyze the limits of funneling efficiency in realistic device geometries. The funneling efficiency in realistic monolayer TMDCs is found to be low, $ <5 \;\%$ both at room and low temperatures. This results from dominant diffusion at room temperature and short exciton lifetimes at low temperatures. On the other hand, in TMDC heterostructures with long exciton lifetimes the funneling efficiency reaches $\sim 50\;\%$ at room temperature, as the exciton density reaches thermal equilibrium in the funnel. Finally, we show that Auger recombination limits funneling efficiency for intense illumination sources.