Investigating the impact of heat treatment on the structural, optical, and electrical characteristics of Zn₂₀Se₈₀ thin films

In this work, Zn₂₀Se₈₀ thin films (TFs) were fabricated via a vacuum evaporation technique, with the deposition taking place on a glass substrate under a vacuum pressure of 10⁻⁵ Torr. Various thermal analyses were conducted to ascertain crucial parameters such as the glass transition temperature (T_g), crystallization onset temperatures (T_c), and peak temperature (T_p). The characterization of the films involved the assessment of parameters like crystallite size, strain, and dislocation density through a variance analysis of X-ray diffraction (XRD) line profiles for both the as-deposited and differently annealed Zn₂₀Se₈₀TFs. A spectrophotometer was employed for measuring the transmittance (T) and reflectance (R) properties under normal incidence for both the as-deposited and annealed TFs. The direct transition of the optical bandgap (E_g) and Urbach energy (E_U) were determined based on the absorption coefficient values. Moreover, the refractive index (n) and extinction coefficient (k_ex) were extracted from the R and T measurements utilizing analytical relationships. Additionally, the Wemple-DiDomenico model was utilized to extract the dispersive (E_d) and oscillator (E_o) parameters. Furthermore, the electrical conductivity and activation energy were analyzed using the Arrhenius formula.