ReaxFF reveals how SiC vapor composition changes during high-temperature crystal growth 

Silicon carbide is a key material for high-power electronics, but growing large, high-quality SiC crystals remains challenging. In physical vapor transport growth, temperature and vapor composition strongly affect crystal quality, while the extreme furnace conditions make the underlying processes difficult to observe experimentally.

In this study, researchers developed a refined ReaxFF force field for Si/C chemistry and used AMS molecular dynamics simulations to study SiC sublimation from 3000 to 4500 K. The force field was trained against quantum-mechanical data covering SiₓCᵧ clusters as well as crystalline SiC, enabling simulations of both condensed material and reactive vapor species.

The simulations show a clear change in vapor composition with temperature. Larger clusters such as Si₂C₂, Si₂C₃, and Si₃C₂ are more stable at lower temperatures, while higher temperatures favor smaller species such as Si, SiC₂, and Si₂C. ReaxFF also predicts Si-rich early sublimation at 3000 K, helping explain the progressive carbon enrichment of the remaining material observed experimentally.

The refined ReaxFF model performed particularly well for the low-coordination SiₓCᵧ species important during sublimation. By also extracting Arrhenius parameters for key reactions, the study connects atomistic reaction chemistry with kinetic models that can ultimately feed into computational fluid dynamics simulations of SiC crystal growth.

For SiC materials R&D, AMS and ReaxFF provide a way to connect atomistic sublimation chemistry with process-scale crystal growth modeling, helping reveal which vapor species form, how they change with temperature, and how these processes may influence growth conditions.