Physico-chemical properties of the thin films of the SbxSe100 − x system (x = 90, 85, 80)

Abstract

The bulk samples of SbxSe100−x system (x=90, 85, 80) and their amorphous thin films were prepared by flash evaporation method. The films possess good thermal stability and high values of the activation energy of crystallization. The activation energy of crystallization (Ea) of the thin films Sb85Se15 and Sb80Se20 was found to be 2.97 and 2.55eV, respectively. The Ea of Sb90Se10 was found to be 1.79eV for first step and 2.95eV for second step. The homogeneous thin amorphous films were crystallized by nanosecond laser pulses, by annealing at 235 and 360°C and during the measurement of temperature dependence of electrical resistivity. The crystalline phase possesses much lower electrical resistivity than the amorphous one (ΔRs≈103); the temperature of crystallization Tc is from the region of 150–161°C. The structure of prepared films as determined by X-ray diffraction analysis revealed that the films crystallized by laser pulses and by annealing at 235°C contain only one phase of Sb-like structure. The films of composition Sb80Se20 and Sb85Se15 annealed at 360°C contain two phases of Sb and Sb2Se3. The film of composition Sb90Se10 annealed at 360°C contains one phase of Sb-like structure. The optical reflectivity change due to crystallization is also large (ΔRopt.≈20–30%). The refractive index n of crystalline samples is higher than that of amorphous films (Δn≈1.5–3.1 for transparent part of spectrum); it is higher for films with higher Sb content. The real and imaginary parts of permittivity, evaluated from ellipsometric measurement, are also much higher for crystalline state (up to 55) than for the amorphous one (<33). The amorphous films are semiconductive, and their Egopt. (0.28–0.35eV) is decreasing with an increasing content of Sb. In spectral region of λ=360–830nm, the real part of permittivity of crystalline phase is negative and the imaginary part of permittivity is not high, especially for the Sb90Se10 samples. Such films are perspective not only as the phase change materials, but also as the plasmonic materials.