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

Abstract

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