Thickness-Dependent Nonadiabatic Recombination in MoSTe/hBN Heterostructures: An Ultrafast Dynamic Study

When a transition metal dichalcogenide monolayer is encapsulated by hexagonal boron nitride (hBN), the introduced dielectric screening can change its electronic and optical properties. Using time-dependent density functional theory with nonadiabatic molecular dynamics, the electron–hole nonradiative recombination process in hBN-encapsulated MoSTe is investigated. The heterostructures feature a type-I band alignment. Noteworthily, the incorporation of hBN into the system introduces high-frequency vibrational modes at 800 cm–1, thereby facilitating the electron–hole recombination when compared with the MoSTe monolayer. Nevertheless, as the thickness of hBN increases, a larger proportion of low-frequency vibrational modes below 100 cm–1 is excited within the system, consequently suppressing electron–hole recombination. This observation was further corroborated by employing the frozen phonon method. Our findings provide significant insights for the design and enhancement of photoelectronic devices.