Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl2O4) ceramic target

Using a highly conductive ZnO(ZnAl₂O₄) ceramic target, c-axis-oriented transparent conductive ZnO:Al₂O₃ (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10⁻⁴ Ω cm and can be further reduced to as low as 1.5×10⁻⁴ Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10⁻⁵ Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).     

Growth,electrical and optical behaviour of nanocrystalline Ag2Cu2O3 films produced by RF magnetron sputtering

Thin films of Ag₂Cu₂O₃ were formed on glass substrates by RF magnetron sputtering technique under different oxygen partial pressures in the range 5 × 10^‐3 – 8 × 10^‐2 Pa using mosaic target of Ag₇₀Cu₃₀. The influence of oxygen partial pressure on the core level binding energies, crystallographic structure, and electrical and optical properties of the deposited films was studied. The atomic ratio of copper to silver in the films was 0.302. The oxygen content was in correlation with the oxygen partial pressure maintained during the growth of the films. The films formed at oxygen partial pressures < 2 × 10^‐2 Pa was mixed phase of Ag₂Cu₂O₃ and Ag. The films deposited at 2 × 10^‐2 Pa were single phase of Ag₂Cu₂O₃. The crystallite size of the films formed at 2 × 10^‐2 Pa was 12 nm, while those films annealed at 473 K was 16 nm. The nanocrystalline Ag₂Cu₂O₃ films formed at oxygen partial pressure of 2 × 10^‐2 Pa showed electrical resistivity of 8.2 Ωcm and optical band gap of 1.95 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the structure of thin rhenium films

The phase composition of thin rhenium films as depending on deposition conditions has been studied. In films deposited at a pressure of 10⁻⁵ torr impurity phases with simple cubic and hexagonal lattices were found. In films evaporated at a pressure of 10⁻⁸ torr only an hep phase equilibrium in bulk samples is formed. It has been concluded that in thin rhenium films no transitions to a fcc phase occurs. In the present work the dependence of thin film phase composition was investigated as a function of film thickness (∼5–500 Å), deposition rate (∼0.1–10 Å/sec) and substrate temperatur (∼ 20–450°C). The films were deposited on NaCl single crystals at a pressure of 10⁻⁵ torr (oil diffusion pump evacuation) an 10⁻⁸ torr (“Orbitron”-type pump evacuation). The measurement of film thickness was conducted by the optical interference method.     

Influence of thermal annealing on the composition and structural parameters of DC magnetron sputtered titanium dioxide thin films

Titanium dioxide films have been deposited using DC magnetron sputtering technique. Films were deposited onto RCA cleaned p‐silicon substrates at the ambient temperature at an oxygen partial pressure of 7 × 10^–5 mbar and sputtering pressure of 1 × 10 ^–3 mbar. The deposited films were annealed in the temperature range 673–873 K. The structure and composition of the films were confirmed using X‐ray diffraction and Auger electron spectroscopy. The structure of the films deposited at the ambient was found to be amorphous and the films annealed at 673 K and above were crystalline with anatase structure. The lattice constants, grain size, microstrain and the dislocation density of the film are calculated and correlated with annealing temperature.     

Pressure Dependence of C–V Curve for Ferroelectric PbTiO3 Thin Films Prepared by RF Multi-target Magnetron Sputtering

Lead titanate thin films were prepared in-situ by RF magnetron sputtering method in the substrate temperature region of 550 °C ˜ 650 °C using Ti and Pb metal targets and oxygen gas. The films deposited at 650 °C for 60 min – when the applied power to the Ti and Pb target and deposition pressure were 200 W, 40 W, and 1.8 × 10⁻² Torr, respectively — had stoichiometric composition ratio and shown X-ray diffraction patterns of tetragonal structure like that of the powder. For the application to the piezoelectric field effect transistor (PI-FET), the substrate of SiO₂ (50 nm)/p-Si(100) was used. Leakage current density of the thin film was 7 × 10⁻⁸ A/cm² at 100 kV/cm, dielectric breakdown voltage was 1.8 MV/cm, and so it showed high insulator characteristics. Capacitance-voltage curve was measured as a function of pressure. The variation width of the capacitance was 6.5 pF at bias voltage of –4 volts, and the value increased linearly according to the pressure up to about 6 kgf/cm², and was saturated at the pressure of 8 kgf/cm².     

Spray deposition and characterization of undoped and In‐doped tin disulphide thin films

Undoped and Indium doped tin disulphide (SnS₂) thin films had been deposited onto glass substrates at T_s = 300 °C using spray pyrolysis technique under atmospheric pressure with stannous chloride, indium chloride and thiourea as precursors. The structural, optical and electrical properties of the deposited films were characterized. The XRD pattern revealed that the undoped and doped films had preferred orientation along (002) plane with hexagonal structure. FESEM micrographs had shown that morphologies of the films changed with indium doping. Optical constant such as refractive index (n), extinction coefficient (k), real and imaginary parts of dielectric constants were evaluated from transmittance and reflectance spectra in UV‐Visible spectroscopy. The optical absorption data were used to determine the band gap energy and it was found to be 2.75 eV for undoped and 2.50 eV for indium doped films respectively. The room temperature dark resistivity was found to be 4.545 × 10³ Ω‐cm and 5.406 × 10³ Ω‐cm for undoped and In‐doped films respectively.     

Effect of calcination on the crystallinity of sputtered TiO2 thin films as studied by Raman scattering

Titanium dioxide films have been deposited using DC magnetron sputtering technique onto silicon substrates at an ambient temperature and at an oxygen partial pressure of 7 × 10 ^–5 mbar and sputtering pressure (Ar + O₂) of 1 × 10 ^–3 mbar. The deposited films were calcinated at 673 and 773 K. The composition of the films as analyzed using Auger Electron Spectroscopy (AES) revealed the stoichiometry with an O and Ti ratio of 2.08. The influence of post‐deposition calcination on the Raman scattering of the films was studied. The existence of Raman active modes A_1g, B_1g and E_g corresponding to the Raman shifts are reported in this paper. The improvement of crystallinity of the TiO₂ films as shown by the Raman scattering studies has also been reported. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

InOx semiconductor films deposited on glass substrates for transparent electronics

Transparent undoped semiconductor indium oxide films were deposited by radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium at low substrate temperature. It was experimentally verified that the variation of rf power density has a strong influence on the electrical and structural properties of the films. The thickness of the InO_x films is of about 100 nm. Results show that InO_x films show an average visible transmittance of about 85% and energy gap of about 2.6 eV. Structural and electrical conductivity measurements show that films are polycrystalline and there exists a linear variation of conductivity logarithm vs reciprocal of temperature. Electrical conductivity variation of 17.6 to 5.8 × 10⁻³ (Ω cm)⁻¹ for films produced at rf power densities ranging from 3.9 to 78.1 mW cm⁻³ was obtained. This controllable semiconductor behavior can therefore satisfy the requirement of a particular application for these type of films.     

The effect of oxygen partial pressure on physical properties of nano‐crystalline silver oxide thin films deposited by RF magnetron sputtering

Nano‐crystalline silver oxide films were deposited on glass and silicon substrates held at room temperature by RF magnetron sputtering of silver target under different oxygen partial pressures. The influence of oxygen partial pressure on the structural, morphological, electrical and optical properties of deposited films was investigated. Varying oxygen partial pressure during the sputter deposition leads to changes of mixed phase of Ag₂O and Ag to a single phase of Ag₂O and to AgO. The X‐ray diffraction and X‐ray photoelectron spectroscopy results showed the formation of single phase Ag₂O with cubic structure at oxygen partial pressures of 2x10^‐2 Pa while the films deposited at higher oxygen partial pressure of 9x10^‐2 Pa showed the formation of single phase of AgO with monoclinic structure. Raman spectroscopic studies on the single phase Ag₂O showed the stretching vibration of Ag‐O bonds. Single‐phase Ag₂O films obtained at oxygen partial pressure of 2x10^‐2 Pa were nano‐crystalline with crystallite size of 20 nm and possessed an electrical resistivity of 5.2x10^‐3 Ωcm and optical band gap of 2.05 eV. The films deposited at higher oxygen partial pressure of 9x10^‐2 Pa were of AgO with electrical resistivity of 1.8x10^‐2 Ωcm and optical band gap of 2.13 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of selenization temperature on synthesis,morphology, and properties of nanostructured CoSe2 films

Nanostructured cobalt selenide (CoSe₂) thin films were deposited on a glass substrate using the selenization of Co films at different selenization temperatures (300 °C, 400 °C, and 500 °C) in a pure Se vapor for two hours. The morphology and structure of the as‐deposited films shows that the film morphology and crystallinity are affected by the selenization temperature. Increasing the selenization temperature from 300 °C to 400 °C and 500 °C results in a change in the surface and cross sectional morphology. At 300 °C, the Co films have an almost amorphous structure, while at temperatures of 400 and 500 °C, the Co films have a crystalline nanostructure with bilayered morphology. Optical analyses of the CoSe₂ films at 500 °C show a large absorption (α > 1.0 × 10⁵ cm⁻¹) and a direct band gap (∼1.0 eV).     

Influence of oxygen partial pressure on the properties of undoped InOx films deposited at room temperature by rf-PERTE

Transparent and conductive/semiconductive undoped indium oxide (InO_x) thin films were deposited at room temperature. The deposition technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied between 3 × 10^?2 and 1.3 × 10^?1 Pa. Undoped InO_x films, 100 nm thick, deposited at the oxygen partial pressure of 6 × 10^?2 Pa show a conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7 eV and an electrical conductivity of about 1100 (Ω cm)^?1. For oxygen pressures greater than 6 × 10^?2 Pa, semiconductive films are obtained, maintaining the visible transmittance. Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6 × 10^?2 Pa show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases.     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Microstructural and optoelectrical properties of transparent conducting ZnO:Al thin films for organic solar cells

The Al‐doped zinc oxide (ZnO:Al) thin films were grown on glass substrates by the magnetron sputtering technique. The films were characterized with X‐ray diffractometer, four‐point probe and optical transmission spectroscopy, respectively. The dependence of microstructural, electrical and optical properties on deposition temperature was investigated. The results show that all the films have hexagonal wurtzite structure with highly c‐axis orientation. And the microstrural and optoelectrical properties of the films are observed to be subjected to the deposition temperature. The ZnO:Al film prepared at the deposition temperature of 650 K possesses the best optoelectrical properties, with the lowest electrical resistivity (6.1×10⁻⁴ Ω·cm), the highest average visible transmittance (85.3%) and the maximum figure of merit (0.41 Ω⁻¹). The optical energy gap of the films was estimated from Tauc's law and observed to be an increasing tendency with the increment of the deposition temperature. Furthermore, the refractive index of the films was determined by the optical characterization methods and the dispersion behavior was studied by the single electronic oscillator model.     

The growth of high-quality MCT films by MBE using in-situ ellipsometry

The ellipsometry and RHEED study of high-quality MCT films grown on (112)- and (130) CdTe and GaAs by MBE was carried out. The dependence of the ellipsometric parameter ψ on MCT composition is evaluated. It was shown that such parameters as growth rate, the surface roughness, initial substrate temperature, and film composition may be measured by the in-situ ellipsometry. The appearance of surface roughness was observed in the initial stage of MCT growth under various compositions (x_CdTe = 0 ÷ 0.4). The further growth at optimum conditions leads to the smoothing of the surface and supplies us with high-quality MCT films. The concentration, mobility, and life time of carriers in MCT films were respectively: n = 1.8 × 10¹⁴ ÷ 8.2 × 10¹⁵ cm⁻³, μ_n = 44000 ÷ 370000 cm² V⁻¹ s⁻¹, τ_n = 40 ÷ 220 ns; p = 1.8 × 10¹⁵ ÷ 8.4 × 10¹⁵ cm⁻³, μ_p = 215 ÷ 284 cm² V⁻¹ s⁻¹, τ_p = 12 ÷ 20 ns.     

Transparent thin film transistors based on indium oxide semiconductor

Indium oxide films were deposited by radio-frequency plasma enhanced reactive thermal evaporation (rf-PERTE). The combined use of rf power and oxygen pressure allowed the control of the crystallite size in the film, changing the optical and electrical properties. The films obtained have electrical resistivity ranging from 13.7 to 1.7 × 10⁷ Ω cm. Transparent TFTs made with those films as semiconducting and conducting layers, respectively, present threshold voltages near 2 V and on/off ratios of 10⁴.     

Influence of hydrogen on the thermomechanical properties of a-CNx:H and a-CNx films deposited by glow discharge and ion beam assisted deposition

The coefficient of thermal expansion (CTE), Young’s modulus, Poisson’s ratio, stress and hardness of a-CN_x and a-CN_x:H were investigated as a function of nitrogen concentration. Hydrogenated films were prepared by glow discharge, GD, and unhydrogenated films were prepared by ion beam assisted deposition, IBAD. Using nanohardness measurements and the thermally induced bending technique, it was possible to extract separately, Young’s modulus and Poisson’s ratio. A strong influence of hydrogen, in a-CN_x:H films, was observed on the CTE, which reaches about ∼9 × 10⁻⁶ C⁻¹, close to that of graphite (∼8 × 10⁻⁶ C⁻¹) for nitrogen concentration as low as 5 at.%. On the other hand, the CTE of unhydrogenated films increases with nitrogen concentration at a much lower rate, reaching 5.5 × 10⁻⁶ C⁻¹ for 33 at.% nitrogen.     

Properties of oriented TTF-TCNQ thin films

Vapour deposited thin films of the organic molecular complex tetrathiafulvaliniumtetracyanoquinodimethane (TTF-TCNQ) are investigated by electrical and electronmicroscopical methods. Morphology studies by means of electron micrographs show, that the thin films up to thicknesses of 300 nm consist of small crystals of a size of 1.2 · 0.2 μm² (deposited on cleaved (100) faces of NaCl) or 15 · 2 μm² (on glass substrate). Dependend on deposition conditions and on material of the substrate thin films are produced with strong or statistic orientation of this crystals. Strong oriented thin films exhibit conductivities up to σ = 65 ω⁻¹ cm⁻¹ and activation energies of W_A = 0.02 eV. The found dependences of the conductivity on electrical field strength. temperature, and size of microcrystals are explained by a linear hopping model.     

Microstructure optical and electrical studies of cadmium selenide thin films

Nucleation and growth of cadmium selenide thin films are of considerable interest because of their direct effect on the optical and electrical properties of this material. Vacuum-deposited layers on amorphous and crystalline substrates showed a polycrystalline structure. The layers were deposited at a pressure of 10⁻⁴ Pa, with two deposition rates of 12 nm/s and 15 nm/s. The electrical resistivity and the optical absorption were studied for a group of layers on quartz substrate. As well the morphology and the microstructure were investigated by X-ray and electron microscopy. Few activation energies were estimated from the optical absorbance and thermo-resistance.     

Physical Properties of Zinc Oxide Films Prepared by dc Reactive Magnetron Sputtering at Different Sputtering Pressures

Thin films of zinc oxide were deposited by dc reactive magnetron sputtering onto glass substrates held at a temperature of 663 K and oxygen partial pressure of 1x10^‐3 mbar, and at different sputtering pressures in the range 3x10^‐2 ‐ 10x10^‐2 mbar. The effect of sputtering pressure on the structural, electrical and optical properties of the films were systematically studied. The films were polycrystalline in nature with preferred (002) orientation. The temperature dependence of Hall mobility indicated that the grain boundary scattering of the charge carriers are predominant in these films. The films formed at a sputtering pressure of 6x10^‐2 mbar showed a low electrical resistivity of 6.9x10^‐2 Ohm cm, optical transmittance of 83% with an optical band gap of 3.28 eV.     

Structural and optoelectrical properties of Ga‐doped ZnO semiconductor thin films grown by magnetron sputtering

Transparent conductive gallium‐doped zinc oxide (Ga‐doped ZnO) films were prepared on glass substrate by magnetron sputtering. The influence of substrate temperature on structural, optoelectrical and surface properties of the films were investigated by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), spectrophotometer, four‐point probe and goniometry, respectively. Experimental results show that all the films are found to be oriented along the c‐axis. The grain size and optical transmittance of the films increase with increasing substrate temperature. The average transmittance in the visible wavelength range is above 83% for all the samples. It is observed that the optoelectrical property is correlated with the film structure. The Ga‐doped ZnO film grown at the substrate temperature of 400 °C has the highest figure of merit of 1.25 × 10⁻² Ω⁻¹, the lowest resistivity of 1.56 × 10⁻³ Ω·cm and the highest surface energy of 32.3 mJ/m².