Low-temperature photocarrier dynamics in single-layer MoS2 flakes

摘要

The dichalcogenide MoS2, which is an indirect-gap semiconductor in its bulk form, was recently shown to becomean efficient emitter of photoluminescence as it is thinned to a single layer, indicating a transition to a direct-gapsemiconductor due to confinement effects. With its layered structure of weakly coupled, covalently bondedtwo-dimensional sheets, it can be prepared, just as graphene, using mechanical exfoliation techniques. Here, wepresent temperature-dependent and time-resolved photoluminescence (PL) studies of single-layer MoS2 flakes.Some of the flakes are covered with oxide layers prepared by atomic layer deposition (ALD). At low temperatures,we clearly see two PL peaks in the as-prepared flakes without oxide layers, which we may assign to bound andfree exciton transitions. The lower-energy, bound exciton PL peak is absent in the oxide-covered flakes. Intime-resolved PL measurements, we observe very fast photocarrier recombination on the few-ps timescale at lowtemperatures, with increasing photocarrier lifetimes at higher temperatures due to exciton-phonon scattering.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.