Crystallization behavior in Se₉₀Te₁₀ and Se ₈₀Te₂₀ thin films

Isothermal crystal growth kinetics in Se₉₀Te₁₀ and Se₈₀Te₂₀ thin films was studied by microscopy and in situ X-ray diffraction (XRD) measurements. The spherulite-like crystals grew linearly with time. In a narrow temperature range of between 65 and 85°C, crystal growth rates exhibit simple exponential behavior with activation energies E _G=193±4kJ mol^-1 for Se₉₀Te₁₀ and E_G=195±4kJ mol^-1 for Se₈₀Te ₂₀. The crystal growth in both compositions is controlled by liquid-crystal interface kinetics and can be described by a screw dislocation growth model. From the XRD data, the crystallization fraction was estimated. The crystallization data were described by Johnson-Mehl-Avrami (JMA) model with Avrami exponents m=1.4±0.3 for Se₉₀Te₁₀ and m=1.6±0.4 for Se₈₀Te₂₀. Activation energies were estimated from the temperature dependence of rate constant evaluated from the JMA model. The activation energies of nucleation-growth process were found to be E_c=184±21kJ mol^-1 for Se₉₀Te ₁₀ and E_c=179±7kJ mol^-1 for Se ₈₀Te₂₀, and are comparable with activation energies of crystal growth.