Keywords:Exciton, Exciton interactions, Black phosphorus
Exciton-exciton annihilation depends on the dimensionality of the semiconductor system. For example, the annihilation rate is time-dependent for one-dimensional (1D) semiconductors like Carbon nanotubes but is time-independent for two-dimensional (2D) semiconductors such as Molybdenum disulfide. A particularly interesting case is presented by excitons in black phosphorus (BP), where quasi-1D excitons have been observed in atomically thin sheets of BP, resulting in a unique system of 1D excitons in a 2D plane. Here we show that the exciton-exciton annihilation process in bilayer black phosphorus can be tuned from 1D- to 2D-like in nature by controlling initial exciton density and temperature using micro-transient spectroscopy. Our results agree well with an anisotropic diffusion-limited exciton-exciton annihilation model.