Charge Trapping Dynamics in Amorphous Silicon Nitride: A Nonadiabatic TDDFT-MD Perspective

Understanding charge trapping in amorphous silicon nitride (a-SiNₓ) is essential for improving the reliability of charge-trap flash memory devices. Conventional models attribute charge trapping to dangling bonds, but recent first-principles studies indicate that structural reorganization may play a dominant role. In this work, we employ linear-response TDDFT combined with fewest-switches surface hopping (FSSH) to investigate how electron injection into the conduction-band states of a-SiNₓ drives localized structural rearrangements associated with charge trapping. This approach captures nonadiabatic electron–ion coupling during excited-state relaxation, revealing that injected electrons induce transient bond breaking and formation on a sub-picosecond timescale, which stabilize into persistent trap sites. The results provide atomistic insight into how electronic excitations dynamically couple with atomic motion, establishing a mechanistic foundation for charge retention and guiding the design of next-generation nonvolatile memory materials.