Swanepoel Envelope Method Research Articles

Dependence of solution molarity on structural, optical and electrical properties of spin coated ZnO thin films

Zinc oxide (ZnO) thin films were deposited on glass substrates through spin coating technique. Zinc acetate dihydrate, monoethanolamine and 2-methoxyethanol were used as the starting material, stabilizer and solvent, respectively. The effect of precursor concentration on the structural, optical and electrical properties of ZnO thin films is investigated. The X-ray diffraction studies reveal that all the films are polycrystalline in nature with preferred (002) orientation with crystallite size ranging from ~25 to 32 nm. Atomic force microscopy images infer the columnar growth of the films. From the optical measurements it was found that there was a marginal decrease in the band gap energy with increase in molarity up to 0.7 M. Optical constants and thickness of the films were found with the help of Swanepoel envelope method and were verified through ellipsometric measurements. Electrical resistivity of the grown films was found to be in the range 29–244 Ω cm, with a lowest value obtained for the films grown at 0.7 M. Carrier concentration of the grown films has also followed a similar trend. On the other hand, the Hall effect mobility (~400 cm2/Vs) was highest for the films grown at 0.7 M. Such high values make these films potential candidates for photovoltaic and display applications.

Optical properties of amorphous and polycrystalline Sb2Se3 thin films prepared by thermal evaporation

Sb2Se3 is a very promising photovoltaic material because of its attractive material, optical and electrical properties. Very recently, we reported a superstrate CdS/Sb2Se3 solar cell with 5.6% certified efficiency. In this letter, we focused on the optical properties of amorphous and polycrystalline Sb2Se3 thin films prepared by thermal evaporation. Using temperature dependent transmission spectrum and temperature dependent photoluminescence, the indirect optical transition nature and bandgap values as functions of temperature were acquired. Using ellipsometry measurements and Swanepoel's envelope method, the refractive indices as well as the dielectric constant in a wide wavelength range of 193–2615 nm were obtained. These works would lay the foundation for the further development of Sb2Se3 thin film solar cells.

Dispersion and optical properties of thermally deposited Se91 − xTe9Px (x = 0, 10) films

Se91Te9 and Se81Te9P10 bulk glasses have been prepared by melt-quench technique. The amorphous nature of the as-prepared alloys is confirmed by using X-ray diffraction patterns. Thin films of Se91Te9 and Se81Te9P10 are prepared on chemically cleaned glass substrates by thermal evaporation under vacuum. Differential scanning calorimetery revealed a higher glass transition temperature for Se91Te9 in comparison to Se81Te9P10 bulk glasses. Transmission spectra of the as-prepared films are measured at normal incidence in the wavelength range of 300–2500nm. Refractive index and the film thickness were determined from optical transmittance data using Swanepoel envelope method. It was found that the refractive index dispersion data obeys the single oscillator Wemple and DiDomenico model from which the dispersion parameters were determined. The single oscillator energy, the dispersion energy, the high frequency dielectric constant and the ratio of free charge carrier concentration to the effective mass are then estimated as a function of alloy composition. Analysis of the spectral behavior of the absorption coefficient revealed an allowed indirect optical band gap in this alloy system. With phosphorus incorporation, the optical band gap is found to decrease along with a subsequent increase in the refractive index. The ensemble of these results is interpreted in terms of the chemical bond approach, electronegativity difference of the atoms, cohesive energy and overall mean bond energy.

Optical Properties of Zinc Oxide (ZnO) Thin Films Prepared by Spray Pyrolysis Method

Zinc oxide (ZnO) thin films were deposited on the glass substrates using Zinc acetate dehydrate solution through spray pyrolysis method. The films were obtained by spraying 0.05M concentrated solution at a rate of 0.5ml for 10 min and were deposited at different substrate temperatures ranging from 473K to 673K. A comprehensive study was carried out to realize the effect of substrate temperatures and subsequent annealing on optical properties of the ZnO thin films. It was observed that the band gap energy decreases with increases the substrate temperature and annealing. Optical constants such as the refractive indexnand extinction coefficientkwere determined from transmittance spectrum in the ultravioletvisible (UVVIS) regions by Swanepoel envelope method and crystallinity was confirmed by Urbach tail and atomic force microscope images.

Photo- and Thermo-Induced Changes in Optical Constants and Structure of Thin Films from GeSe2-GeTe-ZnTe System

We examined the condition of preparation of thin films from GeSe2-GeTe-ZnTe system by thermal evaporation and changes in their optical properties after exposure to light and thermal annealing. The results for composition analysis of thin films showed absence of Zn independently of the composition of the bulk glass. By X-ray diffraction (XRD) analysis it was found that a reduction of ZnTe in ZnSe in bulk materials takes of place during the film deposition. A residual from ZnSe was observed in the boat after thin film deposition. Optical constants (refractive index, n and absorption coefficient, α) and thickness, d as well as the optical band gap, E g , depending of the content of Te in ternary Ge-Se-Te system are determined from specrophotometric measurements in the spectral range 400-2500 nm applying the Swanepoel's envelope method and Tauc's procedure. With the increase of Te content in the layers the absorption edge is shifted to the longer wavelengths, refractive index increases while the optical band gap decreases from 2.02 eV for GeSe 2 to 1.26 eV for Ge 34 Se 42 Te 24 . The values of the refractive index decrease after annealing of all composition and E g increase, respectively. Thin films with composition of Ge 27 Se 47 Te 9 Zn 17 and Ge 28 Se 49 Te 10 Zn 13 were prepared by co-evaporation of (GeSe 2 ) 78 (GeTe) 22 and Zn from a boat and a crucible and their optical properties, surface morphology and structure were investigated. The existence of a correlation between the optical band gap and the copostion of thin films from the system studied was demonstrated.

Optical properties of porous chalcogenide films for sensor application

The object of the present work is investigation of the optical properties of obliquely deposited thin films from As – S – Ge system. Aiming to obtain high porous coatings the deposition rate was varied in the range of 0.05–10 nm/s. The conditions for deposition of thin As – S – Ge films with columnar structure and high porosity were established. The role of the actual deposition conditions on the optical properties is examined. The optical constants (refractive index, n and absorption coefficient, α) and thickness, d as well as the optical band gap, Eg, and slope parameter B in dependence of the deposition angle and rate are determined from specrophotometric measurements in the spectral range 400–2000 nm applying the Swanepoel's envelope method and Tauc's procedure. Increasing of the value of n from 2.40 to 1.83 for thin film with composition As10Ge30S60 with increasing deposition angle from 0° to 75° is observed. The possibility of using the thin films for optical sensing of SO2 and H2S was examined. Reversible changes of the refractive index, Δn = 0.015 were observed as a consequence of treatment virgin – exposure to H2SO4 vapors– annealing at 120 °C.

Determination and analysis of dispersive optical constants of CuIn3S5 thin films

CuIn3S5 thin films were prepared from powder by thermal evaporation under vacuum (10−6mbar) onto glass substrates. The glass substrates were heated from 30 to 200°C. The films were characterized for their optical properties using optical measurement techniques (transmittance and reflectance). We have determined the energy and nature of the optical transitions of films. The optical constants of the deposited films were determined in the spectral range 300–1800nm from the analysis of transmission and reflection data. The Swanepoel envelope method was employed on the interference fringes of transmittance patterns for the determination of variation of refractive index with wavelength. Wemple–Di Domenico single oscillator model was applied to determine the optical constants such as oscillator energy E0 and dispersion energy Ed of the films deposited at different substrate temperatures. The electric free carrier susceptibility and the ratio of the carrier concentration to the effective mass were estimated according to the model of Spitzer and Fan.

Optical investigation of electron-beam-deposited tungsten-tellurite (TeO2)100− x (WO3) x amorphous films

Amorphous films of (100 − x)TeO2–xWO3 with compositions 7.5 ≥ x ≤ 40 mol. % were prepared by electron-beam evaporation. The compositional dependence of the optical properties of the prepared films was analyzed by the Swanepoel envelope method, which revealed that the refractive index increases with increasing tungsten oxide content. The Wemple–DiDomenico dispersion model was used to explain the refractive index increase in terms of the formation of W−O−Te bonds, which have a higher energy than that of Te−O−Te bonds. A fitting of the spectral dependence of the absorption coefficient to the Tauc relation allowed a determination of the optical band gap, , which is found to decrease linearly with increasing tungsten oxide percentage.

Synthesis and characterisation of Gd-doped BaTiO 3 thin films prepared by laser ablation for optoelectronic applications

The results of gadolinium (Gd)-doped barium titanate (BaTiO 3) thin films prepared by laser ablation on glass and silicon substrates are reported. Rutherford backscattering (RBS) analyses carried out on glass samples indicated the substitution of barium (Ba) by gadolinium (Gd) after annealing, leading to a film with composition Ba 0.76TiGd 0.01O 2.5. There is a reduction in the thickness from 2.21 to 2.02 microns for as-deposited and annealed films. The films on silicon showed a higher degree of crystallinity compared to that of glass substrates due to increased annealing temperature. The average grain size calculated using the X-ray diffraction (XRD) pattern from silicon substrates was 30 nm. The film has a tetragonal structure with a “ c/ a” ratio of 1.03 signifying that the incorporation of Gd in BaTiO 3 led to the elongation of the c-axis. The percentage transmittance reduced from 80 to 50% due to annealing and this is probably due to structural changes in the film. Swanepoel envelope method employed on the interference fringes of the transmittance pattern led to the determination of the variation of the refractive index with wavelength. Sellmier single oscillator model was applied to determine the optical constants of the films on glass substrates. Bandgap analyses carried out showed the reduction in bandgap with annealing and also the possibility that Gd incorporation has modified the film chemistry leading to the existence of direct (4.35 eV) and indirect (3.88 eV) allowed transitions in the annealed films. Dielectric property measurement carried out under ambient conditions gave a relaxation time τ of 1.6×10 −4 s and conduction by small polaron with the onset of polaron conduction set at about 7 kHz. It is conjectured that these properties, especially the high refractive index and the high bandgaps, can make Gd-doped BaTiO 3 a good candidate for optoelectronic applications.

Structural and optical properties of annealed W-dopedBaTiO3 thin films prepared by pulsed laser deposition

Tungsten-doped barium titanate thin films have been prepared on glass and silicon substratesby laser ablation. The films were compositionally, structurally and optically characterized.Rutherford backscattering spectroscopy simulation gave the composition to beBa0.85W0.05Ti0.94O3.2 with acationic ratio (Ba+W)/Ti of 0.95. All the films without annealing were amorphous. The calculated lattice constantsthrough the diffraction patterns on the silicon substrate indicated the high probability ofthe film having a cubic symmetry. Atomic force microscopy results showed the film surfaceto be smooth with a maximum roughness of 5 nm, varied grain size distributionand average grain size of 50 nm. Through the Swanepoel envelope method, therefractive index dispersion was obtained. Maximum and minimum refractive indices of2.6 and 2.32 at 475 and 812 nm, respectively, were calculated. Analysis of thedependence of the refractive index and the dielectric constant on wavelength led to thedetermination of the high-frequency dielectric constant and the carrier density effective mass ratio(Nc/m*). The single-oscillator model proved to be adequate for describing the dispersion behaviour.Through this model, the dispersion parameter, average oscillator parameter and strengthwere determined. The optical band gap obtained on annealed sample was 3.8 eV byassuming a direct transition.