Extraction of thermal and optical parameters for As–Se–Te thin films according to phase-change pathways

Abstract

The technique of thermal evaporation was used to synthesize the As50Se50-xTex (x = 0, 25, and 50 at.%) thin films (∼500 nm). The scenarios of this research were focused on the phase change pathways of the fresh and annealed (at Tc) thin films. By measuring the surface resistance of the studied thin films in the thermal range between 300 and 600 K, the path of phase transitions from the amorphous to the crystalline state was determined. The average activation energy of phase transitions was computed for the entire system. The phase-transition temperature has been determined utilizing the first derivative of the sheet resistance as a function of temperature (Rs–T). The optical bandgap of the fresh and annealed (at Tc) thin films was determined utilizing Kubelka–Munk (K-M) function that was extracted after measuring the diffuse reflectivity spectra in the range of (300–2500 nm). The two molar optical constants (n, k), the molar dispersion and dielectric parameters have been computed. Values of effective plasmon energy (Ψ), Molar volume Vm, the effective number of electrons neff, the electron density parameter rs, the homopolar gap (E‾h), the heteropolar gap (C), the average gap (E‾g), the theoretical static dielectric constant (ε0th) and Phillips ionicity of the glasses under study were calculated according to Penn model. All computed parameters in this work were given to the phase change paths in the studied system to consider the possibility of using the chalcogenide system in the phase-change memory (PCM) applications.