Influence of substrate and film thickness on structural,optical and electrical properties of ZnO thin films

Transparent Zinc Oxide (ZnO) thin films have been grown on Si (100) and Sapphire (0001) substrates by RF magnetron sputtering for different growth time intervals (10, 30 and 60 min) to study the substrate and thickness effects. All the films have been grown at a substrate temperature of 450 °C. It has been found that the average growth rate on Si (100) substrate (8.6 nm/min) is higher than that on Sapphire (0001) substrate (2.6 nm/min) in an identical growth condition which clearly shows the virtual role of substrates. The lower growth rate on Sapphire (0001) suggests that the increasingly ordered and uniform growth due to less lattice mismatch. The grown films have been characterized by X‐ray diffraction (XRD), Reflectance, Photoluminescence (PL) and Hall measurements. The XRD result (FWHM) reveals that for lower growth time, the films grown on Si (100) is better than on Sapphire (0001). Conversely, for higher growth time, the films grown on Sapphire (0001) is better than on Si (100). The variation of strain behavior due to thickness on both substrates has been justified by UV‐Vis reflectance, photoluminescence and Hall effect measurements. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on the properties of vacuum evaporated indium selenide thin films

Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (T_sb = 30°, 400°C). X‐ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 – 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (E_g^opt) 1.56 eV; where as the films formed at 400°C were found to have a E_g^opt of 1.92 eV. The increase in the value of E_g^opt with T_sb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current ‐Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and structural properties of lead iodide thin films prepared by vacuum evaporation method

Thermally processed lead iodide (PbI₂) thin films were prepared by the vacuum evaporation method in a constant ambient. Measured thickness of the film was verified analytically from the optical transmittance data in a wavelength range between 300 and 1600 nm. From the Tauc relation for the non‐direct inter band transition, the optical band gap of the film was found to be 2.58 eV for film thickness 300 nm. X‐ray diffraction analysis confirmed that PbI₂ films are polycrystalline, having hexagonal structure. The low fluctuation in Urbach energy indicates that the grain size is quite small. The present findings are in agreement with the other results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of annealing on the structural,electrical and optical properties of nanostructured TiO2 thin films

Nanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO₂ films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV‐Visible spectroscopy and electrical studies. X‐ray diffraction studies showed that the as‐deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator‐Wemple and Didomenico model. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of precursor concentration on structural,morphological and electrical properties of spray deposited ZnO thin films

Nanostructured ZnO thin films were coated on glass substrate by spray pyrolysis using Zinc acetate dihydrate as precursor. Effect of precursor concentration on structural, morphological, optical and electrical properties of the films was investigated. The crystal structure and orientation of the ZnO thin films prepared with four different precursor solution concentrations were studied and it was observed that, the prepared films are polycrystalline in nature with hexagonal wurzite structure. The peaks are indexed to (100), (002), (101), (102) and (110) planes. Grain size and texture coefficient (TC) were calculated and the grain size found to increase with an increase in precursor concentration. Presence of Zn and O elements was confirmed with EDAX spectra. Optical absorption measurements were carried out in the wavelength region of 380 to 800 nm and the band gap decreases as precursor concentration increases. The current‐voltage characteristics were observed at room temperature and in dark. It was found that for the films deposited at four different precursor concentrations, the conductivity improves as precursor concentration increases. As trimethyl amine TMA is a good marker for food quality discrimination, sensing behavior of the films at an optimized operating temperature of 373 K, towards various concentrations of (TMA) was observed and reported. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of substrate temperature and oxygen/argon flow ratio on the electrical and optical properties of Ga‐doped ZnO thin films prepared by rf magnetron sputtering

Effects of substrate temperature and atmosphere on the electrical and optical properties of Ga‐doped ZnO thin films deposited by rf magnetron sputtering were investigated. The electrical resistivity of Ga‐doped ZnO (GZO) films decreases as the substrate temperature increases from room temperature to 300°C. A minimum resistivity of 3.3 × 10^–4 Ω cm is obtained at 300°C and then the resistivity increases with a further increase in the substrate temperature to 400°C. This change in resistivity with the substrate temperature is related to the crystallinity of the GZO film. The resistivity nearly does not change with the O₂/Ar flow ratio, R for R < 0.25 but increases rapidly with R for R > 0.25. This change in resistivity with R is also related to crystallinity. The crystallinity is enhanced as R increases, but if the oxygen partial pressure is higher than a certain level (R = 0.25 ± 0.10) gallium oxides precipitate at grain boundaries, which decrease both carrier concentration and mobility. Optical transmittance increases as R increases for R < 0.75. This change in transmittance with R is related to changes in oxygen vacancy concentration and surface roughness with R. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,compositional and optical properties of gallium selenide thin films doped with cadmium

Polycrystalline cadmium doped gallium selenide thin films were obtained by the thermal co‐evaporation of GaSe crystals and Cd grains onto glass substrates. The structural, compositional and optical properties of these films have been investigated by means of X‐ray diffraction, energy dispersive X‐ray analysis and UV‐visible spectroscopy techniques, respectively. Particularly, the elemental analysis, the crystalline nature, the energy band gap, the refractive index, the dispersion energy and static dielectric constant have been identified. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct forbidden energy band gap of 1.22 eV. The cadmium doping has caused a significant decrease in the values of the energy band gap and in all the dispersive optical parameters, as well. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructural,optical and electrical properties of GeO2 thin films prepared by sol‐gel method

GeO₂ thin films were prepared by sol‐gel method on ITO/Glass substrate. The electrical and optical properties and the microstructures of these films were investigated with special emphasis on the effects of an annealing treatment in ambient air. The films were annealed at various temperatures from 500 °C to 700 °C. Structural analysis through X‐ray diffraction (XRD) and atomic force microscope (AFM) showed that surface structure and morphological characteristics were sensitive to the treatment conditions. The optical transmittance spectra of the GeO₂/ITO/Glass were measured using a UV‐visible spectrophotometer. All films exhibited GeO₂ (101) orientation perpendicular to the substrate surface where the grain size increased with increasing annealing temperature. The optical transmittance spectroscopy further revealed high transparency (over 70 %) in the wave range 400 – 800 nm of the visible region. At an annealing temperature level of 700 °C, the GeO₂ films were found to possess a leakage current density of 1.31×10^‐6A/cm² at an electrical field of 20 kV/cm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of density of states on optical properties of GaSe thin film

A systematic investigation on the effect of substrate temperature on the structure, optical absorption and density of states of vacuum evaporated gallium monoselenide (GaSe) thin films is reported. The X‐ray diffraction analysis shows an occurrence of amorphous to polycrystalline transformation in the films deposited at higher‐temperature substrates (573K). The compositional analysis is made with Auger Electron Spectroscopy (AES). The thickness of the film (175nm) is measured by a multiple beam interferometery. Optical characteristics of the GaSe sample have been analyzed using spectrophotometer in the photon energy range of 1.0 ‐ 4 eV. The absorption mechanism has been recognized and the allowed indirect as well as forbidden direct transitions have been found. As‐deposited films show two indirect and allowed transitions due to spin‐orbit splitting of the valence band, as reported here for the first time. Low field conduction have enabled us to determine the density of states in amorphous and poly‐GaSe films. The amorphous and polycrystalline GaSe thin films have localized states density values of N (E_F) = 1.686 × 10¹⁷ cm^‐3 eV^‐1 and 1.257 × 10¹⁵ cm^‐3 eV^‐1 respectively. The experimental results are interpreted in terms of variations in the density of localized states due to progressive decrease of the unsaturated bonds during deposition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on structural and materials properties of zirconium nitride films on D9 steel substrates

Thin zirconium nitride (ZrN) films were prepared by using reactive direct current (DC) magnetron sputtering onto D9 steel substrates. XRD technique was employed to study the coatings, observing variations of crystallite size, crystallite texture and lattice constant, as a function of substrate temperature. Chemical states of the ZrN thin films were determined by X‐ray photoelectron microscopy (XPS). AFM picture showed the presence of spherical shaped grains on the top of homogeneous granular surface. The hardness and elastic modulus values were measured by nanoindendation and their values are 18.5 and 343 GPa respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of gamma radiation on the absorption spectra and optical energy gap of Li‐ doped ZnO thin films

We have studied the effect of subsequent gamma (γ) irradiation on the absorption spectra and the optical energy gap of ZnO thin films doped with Li (ZnO:Li). The optical transmission (T) and optical reflection (R) in the wavelength range 190∼800 nm of films deposited at 300 °C on sapphire, MgO or quartz substrates were measured. The dependence of the absorption coefficient α on photon energy hν was determined as a function of γ‐doses. The films show direct allowed interband transition that influenced by the gamma doses. Both the optical energy gap E^opt_g and the absorption coefficient (α) were found to be γ‐dose dependent. The results can be discussed on the basis of γ‐irradiation‐induced defects in the film and on the film structure. The absorption coefficient exhibits exponential dependence on photon energy obeying Urbach's rule in the absorption edge. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of thermoannealing on crystallinity and optical properties of Sb2S3 thin films

Sb₂S₃ thin films are obtained by evaporating of Sb₂S₃ powder onto glass substrates maintained at room temperature under pressure of 2×10^‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb₂S₃ thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E₀, dispersion energy, E_d) were determined. The static refractive index n(0), static dielectric constant, ε_∞, and optical band gap energy, E_g, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of substrate temperature on microcrystalline structure and optical properties of ZnTe thin films

ZnTe thin films were deposited onto well‐cleaned glass substrates kept at different temperatures (Ts = 303, 373 and 423 K), by vacuum evaporation method under the pressure of 10^–5 Torr. The thickness of the film was measured by quartz crystal monitor and verified by the multiple beam interferometer method. The structural characterization was made using X‐ray diffractometer with filtered CuKα radiation. The grain sizes of the microcrystallines in films increases with increase in substrate temperature. The strain (ε), grain size (D) and dislocation density (δ) was calculated and results are discussed based on substrate temperature. Optical behaviour of the film was analyzed from transmittance spectra in the visible region (400–800 nm). The optical transition in ZnTe films is direct and allowed type. The optical band gap energy shows an inverse dependence on substrate temperature and thickness. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of substrate temperature on the structure of ZnO:Al thin films

ZnO: Al films were prepared using low cost spray pyrolysis technique. The dependence of the physical properties on the substrate temperature was studied. The best films obtained at 500°C substrate temperature with preferred [002] orientation. The sheet resistance decreases with increased substrate temperature, and values as low as R_sh = 207 Ω/cm² are reached for substrate temperature of 500°C. The optical transmittance of films increased by increasing the substrate temperature and received to 75% at 500°C. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Role of annealing environment and partial pressure on structure and optical performance of TiO2 thin films fabricated by rf sputter method

Influences of the different annealing ambient (in air, 1 bar, 2 bar, 3 bar and 4 bar oxygen partial pressure) on the titanium dioxide (TiO₂) thin films deposited on soda lime glass by standard radio frequency (rf) magnetron reactive sputtering method at 100 watt were investigated by means of X–ray diffractometer (XRD), ultra violet spectrometer (UV–vis), and Scanning Electron Microscopy (SEM). It was found that either optical properties or energy band gaps of the films enhanced with increase in the oxygen partial pressure up to 3 bar. The energy band gaps of the films (except for the film annealed in 4 bar oxygen partial pressure) became larger than the film annealed in atmospheric pressure. The best transmission was observed for the thin film annealed in 3 bar oxygen partial pressure. Moreover, not only was grain–like structure found to be more dominant than dot–like structure but also growth of anatase phase was observed instead of that of the rutile phase with increasing oxygen partial pressure up to 3 bar. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of CdCl2 treatment on properties of CdTe thin films grown by evaporation at low substrate temperatures

The structural, morphological and optical properties of vacuum‐evaporated CdTe thin films were investigated as a function of substrate temperature and post‐deposition annealing without and with CdCl₂/treatment at 400°C for 30 min. Diffraction patterns are almost the same exhibiting higher preferential orientation corresponding to (111) plane of the cubic phase. The intensity of the (111) peak increased with the CdCl₂/annealing treatment. The microstructure observed for all films following the CdCl₂/annealing treatment are granular, regardless of the as‐deposited microstructure. The grain sizes are increased after the CdCl₂/annealing treatment but now contain voids around the grain boundaries. The optical band gaps, E_g, were found to be 1.50, 1.50 and 1.48 eV for films deposited at 200 K and annealed without and with CdCl₂/treatment at 400°C for 30 min respectively. A progressive sharpening of the absorption edge upon heat treatment particularly for the CdCl₂/treated was observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of annealing on structural,electrical and optical properties of AgGa(Se0.5S0.5)2 thin films deposited by using sintered stoichometric powder

The structural, electrical and optical properties of AgGa(Se_0.5S_0.5 )₂ thin films deposited by using the thermal evaporation method have been investigated as a function of annealing in the temperature range of 450–600 °C. X‐ray diffraction (XRD) analysis showed that the structural transformation from amorphous to polycrystalline structure started at 450 ^oC with mixed binary phases of Ga₂Se₃, Ga₂S₃, ternary phase of AgGaS₂ and single phase of S. The compositional analysis with the energy dispersive X‐ray analysis (EDXA) revealed that the as‐grown film has different elemental composition with the percentage values of Ag, Ga, Se and S being 5.58, 27.76, 13.84 and 52.82 % than the evaporation source powder, and the detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure have been obtained. The optical band gap values as a function of annealing temperature were calculated as 2.68, 2.85, 2.82, 2.83, and 2.81 eV for as‐grown, annealed at 450, 500, 550, and 600 °C samples, respectively. It was determined that these changes in the band gap are related with the structural changes with annealing. The temperature dependent conductivity measurements were carried out in the temperature range of 250‐430 K for all samples. The room temperature resistivity value of as‐grown film was found to be 0.7x10⁸ (Ω‐cm) and reduced to 0.9x10⁷ (Ω‐cm) following to the annealing. From the variation of electrical conductivity as a function of the ambient temperature, the activation energies at specific temperature intervals for each sample were evaluated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,optical, and electrical properties of electron beam evaporated CdSe thin films

CdSe films have been deposited on glass substrates at different substrate temperatures between room temperature and 300 °C. The films exhibited hexagonal structure with preferential orientation in the (002) direction. The crystallinity improved and the grain size increased with temperature. Band gap values are found decreasing from about 1.92 eV to 1.77 eV with increase of the substrate temperature. It is observed that the resistivity decreases continuously with temperature. Laser Raman studies show the presence of 2 LO and 3 LO peaks at 416 cm^‐1 and 625 cm^‐1respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Substrate effect on microstructure and optical performance of sputter‐deposited TiO2 thin films

This study deals with the role of the different substrates on the microstructural, optical and electronical properties of TiO₂ thin films produced by conventional direct current (DC) magnetron sputtering in a mixture of pure argon and oxygen using a Ti metal target with the aid of X–ray diffractometer (XRD), ultra violet spectrometer (UV–vis) and atomic force microscopy (AFM) measurements. Transparent TiO₂ thin films are deposited on Soda lime glass, MgO(100), quartz and sitall substrates. Phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. It is found that the amplitude of interference oscillation of the films is in a range of 77‐89%. The transmittance of the film deposited on Soda lime glass is the smallest while the film produced on MgO(100) substrate obtains the maximum transmittance value. The refractive index and optical band gap of the TiO₂ thin films are also inferred from the transmittance spectra. The results show that the film deposited on Soda lime glass has the better optical property while the film produced on MgO(100) substrate exhibits much better photoactivity than the other films because of the large optical energy band gap. As for the XRD results, the film prepared on MgO(100) substrate contains the anatase phase only; on the other hand, the other films contain both anatase and rutile phases. Furthermore, AFM images show that the regular structures are observed on the surface of all the films studied. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,optical and electrical characterization of HgxCd1‐xTe polycrystalline films fabricated by two‐source evaporation technique

Two‐source thermal evaporation technique was used to prepare Hg_xCd_1‐xTe thin films onto scratch free transparent glass substrates. The structural investigations revealed that thin films were polycrystalline in nature. Transmittance measurements in the wavelength range (500‐2700 nm) were used to calculate optical constants. The analysis of the optical absorption data showed that the optical band gap was of indirect type. In the composition range 0.05 < x < 0.25 the films exhibited an optical band gap between 1.29 and 0.98 eV. In the same composition range the films were p‐type and exhibited a resistivity, which varied between 10² and 10^‐1 Ω‐cm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)