Phase transformations induced in CdTe single crystal by ruby laser pulsed irradiation

Abstract

Phase transitions induced by laser irradiation in CdTe wafers have been studied in situ and experimental and computer simulation methods. The samples were irradiated by ruby laser with pulse duration 80 ns in energy density range from 0.02 to 0.5 J/cm2. Time-resolved reflectivity (TRR) measurements were carried out at the wavelengths of λ1=1.064 μm and λ2=0.532 μm. Dynamics of transmissivity was studied at λ1. Photoluminescence of CdTe, excited by the ruby laser single pulse, was also investigated. The character of TRR transients changes with the increase of irradiation energy density. The changes are more considerable at λ1 than at λ2. The time dependencies of reflectivity are explained by the changes of optical parameters of CdTe in course of laser-induced melting, solidification and evaporation. The experimental data obtained from transmissivity and photoluminescence measurements correlate with those from TRR transients. Laser-induced melting, crystallization and evaporation processes were studied on the basis of the computational solution of a two-phase moving boundary problem with two moving interfaces. The calculated dependency of melt duration on energy density is in a reasonable agreement with experimental data. From our investigation it follows that in the molten state CdTe is characterized by constant or weakly changing reflectivity in the temperature range from Tm to 3000 K.