Defect-Induced Localized Excitons and Raman Modes in Monolayer MoSe2

In monolayer transition metal dichalcogenides, defects, such as chalcogen vacancies, play an important role in determining their properties. Herein, monolayer MoSe2 with varying Se vacancy concentrations is successfully prepared by adjusting the amount of the precursors during the chemical vapor deposition synthesis. The Raman and low-temperature photoluminescence spectra are systematically studied at varying defect concentrations. Furthermore, it is found that Se vacancies introduce in-gap electronic states, leading to distinct localized exciton emissions, which can be engineered by controlling the concentration of Se vacancies. Density functional theory calculations indicate that the observed variations in localized exciton emission are attributed to the change of defect level with increasing defect concentration. The results provide insights into the influence of varying Se vacancy concentrations on defect-induced Raman and PL spectroscopy in MoSe2.