Joés M.F. Ferreira

Bio: Joés M.F. Ferreira is an academic researcher from University of Aveiro. The author has contributed to research in topics: Band gap & Thin film. The author has an hindex of 1, co-authored 1 publications receiving 63 citations.

Microstructural parameters and optical constants of ZnTe thin films with various thicknesses

Abstract: Different thickness of polycrystalline ZnTe films have been deposited onto glass substrates at room temperature by vacuum evaporation technique. The structural characteristics studied by X-ray diffraction (XRD) showed that the films are polycrystalline and have a zinc blende (cubic) structure. The calculated microstructure parameters revealed that the crystallite size increases and microstrain decreases with increasing film thickness. The transmittance and reflectance have been measured at normal and near normal incidence, respectively, in the spectral range 400–2500 nm. For ZnTe films of different thicknesses, the dependence of absorption coefficient, α on the photon energy showed the occurrence of a direct transition with band gap energy E g opt = 2.21 ± 0.01 eV (For ZnTe films of different thicknesses) confirming the independency of deduced energy gap on film thickness. The refractive indices have been evaluated in terms of envelope method, which has been suggested by Swanepoul in the transparent region. The refractive index could be extrapolated by Cauchy dispersion relationship over the whole spectra range, which extended from 400 to 2500 nm. It was observed that the refractive index, n increased upon increasing the film thickness up to 508 nm, lying within the experimental error for further increases in film thickness.

Structural, linear and nonlinear optical properties of co-doped ZnO thin films

Abstract: Different compositions of Co-doped zinc oxide [(Zn(1−x)Co x O) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10)] thin films were evaporated onto highly clean glass substrates by thermal evaporation technique using a modified source. The structural properties investigated by X-ray diffraction revealed hexagonal wurtzite ZnO-type structure. The crystallite size of the films was found to decrease with increasing Co content. The optical characterization of the films has been carried out using spectral transmittance and reflectance obtained in the wavelength range from 300 to 2500 nm. The refractive index has been found to increase with increasing Co content. It was further found that optical energy gap decreases from 3.28 to 3.03 eV with increasing Co content from x = 0 to x = 0.10, respectively. The dispersion of refractive index has been analyzed in terms of Wemple–DiDomenico (WDD) single-oscillator model. The oscillator parameters, the single-oscillator energy (E o), the dispersion energy (E d), and the static refractive index (n 0), were determined. The nonlinear refractive index of the Zn(1−x)Co x O thin films was calculated and revealed well correlation with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system.

Compositional dependence of the optical properties of amorphous Se80 − xTe20Bix thin films using transmittance and reflectance measurements

Abstract: Optical properties of amorphous Se80 − xTe20Bix thin films with different compositions (x = 0, 2, 4, 6 and 8 at.%) deposited by evaporation technique have been investigated by optical spectrophotometry measurements in the wavelength range of 400–2500 nm. An optical characterization method for uniform films based on Swanepoel's ideas (envelope method) has been employed to extract the refractive index n and film thickness d, with accuracies better than 1%. It was found that the refractive index increases with increasing the concentration of Bi at the expense of Se content. The increasing in refractive index n is interpreted in terms of polarizability and the mean coordination number. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–DiDomenico model. The fundamental parameters for the investigated semiconducting thin films Se80 − xTe20Bix e.g. absorption coefficient and band gap are calculated in the strong absorption region of transmittance and reflectance spectra. The possible optical transition in these films is found to be allowed indirect transition with energy gap Egoptdecreases from 1.467 to 1.035 eV with increasing Bi content at expense of Se. Finally, the decrease in the optical band gap with increasing Bi content in Se80 − xTe20Bix has been explained in terms of the chemical bond approach.