Dynamics of optical parameters of silicon and germanium single crystals during two-pulsed nanosecond laser irradiation

The behaviour of optical characteristics, namely the reflectivity and ellipsometric parameters ψ and Δ of silicon and germanium single crystals is investigated experimentally during two-pulsed laser irradiation. A comparison of the experimental data with the results obtained in solving Stefan's nonlinear problem and with the temperature dependences of the measured optical quantities shows that the maximum temperature of the melt surface of a semiconductor is significantly lower than the value predicted by the simple model of laser annealing. The absence of surface overheat may be attributed to hydrodynamic phenomena which can develop in liquid phase in the process of the melting front movement.