Spatiotemporal dynamics of free and bound excitons in CVD-grown MoS_2 monolayer

摘要

We study photoluminescence (PL) spectra and exciton dynamics of the MoS_2 monolayer (ML) grown by the chemical vapor deposition technique. In addition to the usual direct A-exciton line, we observe a low-energy line of bound excitons dominating the PL spectra at low temperatures. This line shows unusually strong redshift with an increase in the temperature and submicrosecond time dynamics suggesting indirect nature of the corresponding transition. By monitoring the temporal dynamics of exciton PL distribution in the ML plane, we observe diffusive transport of A-excitons and measure the diffusion coefficient up to 40 cm~2/s at elevated excitation powers. The bound exciton spatial distribution spreads over tens of micrometers in ～1 μs. However, this spread is subdiffusive, characterized by a significant slowing down with time. The experimental findings are interpreted as a result of the interplay between the diffusion and Auger recombination of excitons.