Identifying the Origin of Defect-Induced Raman Mode in WS2 Monolayers via Density Functional Perturbation Theory

Transition metal dichalcogenides (TMDs) are being actively studied in next-generation semiconductor applications owing to their excellent optoelectronic properties. Therefore, numerous defect-related studies have been conducted to improve TMD quality. In the study of defects, Raman spectroscopy is widely used to obtain information regarding the defects on a surface. A single sulfur-vacancy-induced Raman peak was recently reported. However, the origin of this vibrational mode has not yet been identified. Therefore, quantum mechanical calculations were performed on the sulfur-vacancy-containing supercell structure to elucidate the origin. By calculating the band structure and phonon dispersion, the phonon momentum was obtained, considering the possible scattering of electrons. After comparing the phonon momentum and phonon dispersion, it was identified that the phonon vibrational origin of a single sulfur-vacancy-induced Raman peak is A′1(k).