Influence of dielectric environment on the optical properties of the CVD-grown monolayer WSe2

Regulating excitonic emission in two-dimensional (2D) semiconductors through external perturbations offers an effective route to improving the performance of their optoelectronic devices. Here, we investigate the evolution of exciton and trion emissions in monolayer tungsten diselenide (WSe2) under different dielectric environments using temperature-dependent Raman and photoluminescence (PL) spectroscopy. Through deconvolution of the PL spectra, it is observed that both low temperature and high-dielectric environment facilitate the formation of trions, leading to an increase in their integrated intensity compared with that of the neutral excitons. This phenomenon can be attributed to the higher trion binding energy at low temperature and the dielectric-induced deep-to-shallow transition of defect levels, which modifies the effective charged defect levels in WSe2 and consequently influences the formation and recombination dynamics of the excitons and trions differently. Our results provide deeper insight into the emission mechanisms of excitonic complexes in 2D semiconductors under dielectric environments and offer useful guidance for dielectric engineering of optoelectronic and photonic devices based on transition metal dichalcogenides.