Optical characterization of polycrystalline ZnSe1−xTex thin films using variable angle spectroscopic ellipsometry and spectrophotmetery techniques

Polycrystalline ZnSe1−xTex (0.0≤x≤1.0) thin films were deposited by the electron beam deposition technique on corning glass substrate. Two different techniques, Variable Angle Spectroscopic Ellipsometry (VASE) and spectrophotometry, have been applied and compared for characterization of the optical properties of ZnSe1−xTex films. The film thickness and optical constants (refractive index (n) and extinction coefficient (k)) of polycrystalline ZnSe1−xTex films were obtained by fitting the spectroscopic ellipsometric data (ψ, ∆) using a three-layer model system in the wavelength range from 400 to 1100 nm. Nevertheless, the optical band gap Egopt determined from k values indicating a direct allowed transition. The optical studies of the polycrystalline ZnSe1−xTex films showed that the refractive index increases and the Egopt decreases. It is worth noting that the obtained values of the optical band gap of the different Te doped films remain in between the reported optical energy gap values of the two ends of the solid solution,ZnSe and ZnTe thin films,. Furthermore, the transmittances spectra of the ZnSe1−xTex films are obtained experimentally from spectrophotometry measurements and theoretically calculated using Murmann's exact equation. Comparing the results yielding a fully agreement between experimental and fitted transmittance data.