Numerical analysis on heat transfer characteristics of a silicon film irradiated by pico-to femtosecond pulse lasers

Abstract

This work aims to investigate the heat transfer characteristics of a silicon microstructure irradiated by picosecond-to-femtosecond ultrashort laser pulses from a microscopic point of view. Carrier-lattice nonequilibrium interactions are simulated with a set of governing equations for the carrier and lattice temperatures to obtain the time evolutions of the lattice temperatures, the carrier number densities, and carrier temperatures. In particular, the relaxation time for approaching the thermal equilibrium between carriers and lattices is introduced to estimate duration of the nonequilibrium state. An appropriate regime map to make a distinction between one-peak and two-peak structures is also established for picosecond laser pulses. It is noted that a substantial increase in carrier temperature is observed for pulse lasers of a few picoseconds duration, whereas the lattice temperature rise is relatively small with decreasing laser pulse widths. It is also found that the laser fluence significantly affects the N-3 decaying rate of the Auger recombination, the carrier temperature distribution exhibits two peaks as a function of time due to the Auger heating as well as the direct laser heating of carriers, and finally, both laser fluence and pulse width play an important role in controlling the nonequilibrium between carriers and lattices.