Numerical simulation of ultrafast energy transport in monocrystalline silicon films under femtosecond laser irradiation

The process of the ultrafast energy transport in monocrystalline silicon submicron films irradiated with femtosecond laser was simulated using the carrier transport model based on the Boltzmann transport equation. The effects of different irradiation energy density and laser wavelength on the carrier density and the process of temperature ultrafast variation were investigated. The numerical calculation results show that, irradiated at 800 nm, the incident energy density influences the peaks of the carrier density and temperature only, but the occurrence time of their peaks does not change. The recovery process toward the equilibrium state is hardly influenced by the incident energy density. Under the irradiation of different wavelengths, the higher the photon energy is, the less time the carrier density and temperature take to reach the peak values, the bigger the corresponding peak appears and the faster the attenuation velocity becomes. The time constant of the fast attenuation is equal to the carrier energy relaxation time when the incident photon energy is larger than the band-gap of the monocrystalline silicon.