Study of photoinduced nonthermal melting of 4H-SiC under femtosecond pulse laser irradiation based on time-dependent density functional theory simulations

Silicon carbide (SiC) exhibits superior properties, including a wide bandgap, high breakdown electric field, high thermal conductivity, high electron saturation drift velocity, strong radiation resistance, and excellent chemical stability, making it highly suitable for power device applications. In the substrate slicing process for fabricating SiC power devices, pulsed laser technology provides several advantages over traditional diamond wire sawing, including a smaller heat-affected zone, reduced thermal defects, higher precision, and improved efficiency. To gain a deeper understanding of the interaction between femtosecond lasers and 4H-SiC materials at the atomic scale, this study employs real-time time-dependent density functional theory simulations, incorporating carrier cooling to maintain detailed balance. The analysis examines the evolution of carrier number, density of states, Si–C bond length, and atomic disorder over time under photoexcitation at varying wavelengths and intensities. The results indicate that ultrafast non-thermal melting in 4H-SiC arises from carrier localization, which induces uneven interatomic forces, leading to local atomic displacements, which increases atomic bond lengths and ultimately results in melting. Long-wavelength 1064 nm laser irradiation was found to cause greater atomic force imbalances and displacements than shorter wavelengths (266 and 532 nm), leading to more pronounced non-thermal melting. This study provides atomic-scale theoretical support for research on femtosecond laser processing of 4H-SiC ingots and substrates.