Wave Interference Effect in Thin Film Structures under Pulsed Laser Irradiation

Abstract

The present article conducts extensive numerical simulations to investigate conduction and radiation heat transfer characteristics in thin silicon layers irradiated by pulsed lasers. The two temperature model is used for estimating carrier and lattice temperatures during laser irradiation. The energy absorption in thin films is predicted by the electromagnetic theory, including wave interference effects through thin film optics. The present study predicts the carrier and lattice temperatures during laser irradiation and examines the influence of film thickness and laser pulse duration on characteristics of energy transport. It is observed that, unlike bulk materials, the variation of the film thickness causes significant changes in the reflectivity of silicon film due to wave interference effects in thin film structures. The maximum value of the reflectivity is estimated to be about seven times larger than the minimum value. For the spatial distributions of carrier and lattice temperatures, it is found that a periodic tendency appears for picosecond pulse because of the difference between the pulse duration and the time for energy diffusion. It indicates that the traditional usage of Beer’s law is not appropriate for prediction of radiation heat transfer in thin film structures.