Atomic-Scale Modulation of Charge Carrier Dynamics by Intrinsic Defects in Monolayer MoSi₂N₄

The atomic-scale mechanisms by which intrinsic defects influence charge carrier dynamics in monolayer MoSi₂N₄ remain poorly understood in current studies of this emerging two-dimensional material. By combining first-principles density functional theory (DFT) and ab initio nonadiabatic molecular dynamics (NAMD) simulations, we investigated the static properties and carrier dynamics of MoSi₂N₄ monolayers with and without intrinsic defects. MoSi₂N₄ reveals strong band dispersion near the conduction band minimum, with weak coupling between the K-valley states and other states, leading to delayed electron relaxation and suppressed energy dissipation. Notably, the Mo_Si defect (Mo substituting Si) induces a pronounced spin-polarized lifetime contrast, where spin-down carriers exhibit extended lifetimes in comparison to those in pristine MoSi₂N₄. In contrast, an internal N vacancy introduces deep defect states that significantly accelerate electron-hole recombination. The Si_Mo defect (Si substituting Mo) contributes negligibly to defect-assisted recombination. These findings provide new insights for designing high-performance MoSi₂N₄-based optoelectronic and nanoelectronic devices.