Exciton and trion in few-layer MoS2: Thickness- and temperature-dependent photoluminescence

Molybdenum disulfide (MoS2) is one of the most interesting 2D materials. However, while monolayer MoS2 is well-explored, the few-layer flakes, also promising for flexible device and nano-optoelectronics application,remain less investigated. We study the variation of exciton and trion photoluminescence (PL) and structural properties of few-layer MoS2 grown on SiO2/Si by chemical vapor deposition. Scanning electron and atomicforce microscopies show that most of the flakes have a triangular shape. The ?-PL spectra of the flakes show two broad bands associated to the A exciton overlapped by trion and B exciton. The light emission at room temperature redshifts when the number of layers increases, controlled by ?-Raman spectroscopy. In the temperaturedependent measurements from 80 to 290 K, the PL redshifts according to bandgap narrowing, while the intensity decreases due to the thermally activated nonradiative recombination related to the increase of the electronphonon interaction. Exciton and trion bands are deconvoluted and their behaviors with temperature are studied by fitting the PL data with modelling equations. This allows to evaluate the spin-orbit splitting, quenching activation energy, trion effective size and other important parameters. These new findings are useful for the potential applications of few-layer MoS2 in nano-optoelectronics involving external modulation of optical properties.