Excimer laser melting of GaAs: Real-time optical study

In situ real-time reflectivity measurements have been made in GaAs under ArF excimer laser (λ=193 nm) irradiation. The results obtained provide a reflectivity value for the solid material at the melting temperature of 0.44 and for the liquid of 0.63, both at 633 nm. The reflectivity values obtained for fluences just above the melting threshold (E=225 mJ/cm2) show that melting proceeds inhomogeneously, the near-surface region being formed by a mixture of solid and liquid phases. The comparison of these results to those obtained previously for irradiation of single-crystalline Si and Ge shows that inhomogeneous melting can be a general phenomenon at least in semiconductors. Higher fluences (E≳300 mJ/cm2) are necessary to induce an homogeneous melted layer on the surface of the irradiated material.