Tight-binding modeling of excitonic response in van der Waals stacked 2D semiconductors

Atomically thin transition metal dichalcogenides (TMDCs) exhibit fascinating excitonic properties which are of critical importance for potential applications in nanoscale optoelectronics. In particular, stacked TMDC layers without lattice mismatch allow modulation of their band structures and optoelectronic properties through manipulation of the constituent materials along the stacking direction. Current understanding of TMDC layer-by-layer structures is mainly based on optical measurements and DFT calculations. In this work, we use a phenomenological tight-binding model, combined with DFT calculations, to understand the measured layer-dependent excitonic response of WS₂. This explicit and effective model can quantitatively predict the layer-dependent excitonic states and can also be used to study interlayer excitons (direct and indirect exciton states) in TMDC multilayer structures. In addition, we find that the temperature dependence of the A exciton emission energy of monolayer WS₂ can be well described with the Varshni formula, and that the emission intensity variation with temperature is associated with thermal redistribution of exciton population and increased non-radiative damping due to the enhanced electron-phonon interaction at elevated temperatures.