Deposition of the ZnO transparent electrodes at atmospheric pressure using a DC Arc Plasmatron

Structure and electrical properties of ZnO films deposited by a DC Arc Plasmatron were studied. Films were deposited at atmospheric pressure on a cold substrate. Effect of annealing and plasma treatment was investigated. It was shown that in the as-deposited state the films have an amorphous structure and resistance of about 2 MΩ/cm. Annealing in hydrogen atmosphere at 550 °C improves the crystalline structure and decreases the resistivity of the films down to 5 Ω/cm. Also treatment of surface by hydrogen-argon plasma can be used for decreasing of the resistance of the ZnO films.     

A novel ozone detection at room temperature through UV-LED-assisted ZnO thick film sensors

In this work a novel ozone detection at room temperature (RT) has been investigated. Two functional materials, ZnO and (W_0.9Sn_0.1)O_3 − x (WS10) oxides, have been synthesized to prepare thick film gas sensors, both used in conventional heated mode as well as at RT assisted by UV irradiation. As a source of light, a light emitting diode (LED) of 400 nm peak wavelength was used. Under typical operating conditions of the UV-LED, the radiation flux density ? over the sensor was of about 5 · 10¹⁷ photons/cm². Powders and films have been characterized by means of TG-DTA, SEM, TEM and XRD. Finally, electrical measurements have been performed on sensing films with the aim to compare conductive properties, surface barrier heights and ozone sensing features with and without UV irradiation. Despite the fact that two types of conventional heated sensors offered quite similar results with respect to ozone sensing, it turned out that, at RT and with the assistance of UV light, ZnO behaved excellently fast detecting ozone at concentrations down to 10 ppb, while for WS10 under the same operating conditions an opposite result was observed, i.e. very low response and long response time.     

Preparation and properties of p-type transparent conductive Cu-doped NiO films

The NiO-Cu composite films with various Cu contents of 0-18.17 at.% are deposited on a glass substrate. An ultra high electrical resistivity (ρ) is obtained and cannot be detected by a four point probe measurement when the Cu content in the films is lower than 6.97 at.%. The ρ value is reduced significantly to 35.8 Ω-cm as Cu content is increased to 9.18 at.%, and it further decreases to 0.02 Ω-cm when the Cu content further increases to 18.17 at.%. The Hall measurement for all Cu-doped NiO films shows p-type conduction. In addition, the transmittance of NiO films also decreases continuously from 96% to 43% as Cu content increases from 0 to 18.17 at.%. The XRD patterns of Cu-doped NiO films show that only NiO peaks appear and the crystallinity of NiO films degrades as Cu content exceeds 6.97 at.%. A large amount of lattice sites of Ni²⁺ ions in a NiO crystallite is replaced by the Cu⁺ ions that lead to p-type conduction and result in the degradation of crystallinity for NiO-Cu composite films that have a higher Cu content.     

Electrical properties of quaternary HfAlTiO thin films grown by atomic layer deposition

Quaternary alloyed HfAlTiO thin (~ 4-5 nm) films in the wide range of Ti content have been grown on Si substrates by Atomic Layer Deposition technique, and the effect of both the film composition and the interfacial reactions on the electrical properties of HfAlTiO films is investigated. It is shown that depending on the Ti content, the permittivity and the leakage current density I_leak in HfAlTiO films vary in the range k = 18 ÷ 28 and 0.01-2.4 A cm^− 2, respectively. The incorporation of ultra thin SiN interlayer in Al/HfAlTiO/SiN/Si stack gives rise to the sharp (× 10³) decrease of the I_leak ~ 6 · 10^− 5 A/cm² at the expense of the rather low capacitance equivalent thickness ~ 0.9 nm.     

Effect of process parameters and post deposition annealing on the optical, structural and microwave dielectric properties of RF magnetron sputtered (Ba0.5,Sr0.5)TiO3 thin films

Thin films of (Ba_0.5,Sr_0.5)TiO₃ (BST5) in the thickness range 400-800 nm have been deposited by RF magnetron sputtering on to quartz substrates at ambient temperature. All the properties investigated, i.e. structure, microstructure, optical and microwave dielectric, show a critical dependence on the processing and post processing parameters. The surface morphology as studied by atomic force microscopy reveals ultra fine grains in the case of as deposited films and coarse grain morphology on annealing. The as-deposited films are X-ray amorphous and exhibit refractive index in the range 1.9-2.04 with an optical absorption edge value between 3.8 and 4.2 eV and a maximum dielectric constant of 35 at 12 GHz. The dispersion in refractive index fits into the single effective oscillator model while the variation in the optical parameters with oxygen percentage in the sputtering gas can be explained on the basis of packing fraction changes. On annealing the films at 900 °C they crystallize in to the perovskite structure accompanied by a decrease in optical band gap, increase in refractive index and increase in the microwave dielectric constant. At 12 GHz the highest dielectric constant achieved in the annealed films is 175. It is demonstrated that with increasing oxygen-mixing percentage in the sputtering gas, the microwave dielectric loss decreases while the dielectric constant increases.     

Chemical bath deposition of SnS films with different crystal structures

SnS (stannous sulfide) films were prepared by chemical bath deposition in which a novel chelating reagent ammonium citrate was used. The film has a zinc blende structure or orthorhombic structure which is determined by the pH value of the deposition solution (zinc blende structure at pH = 5 and orthorhombic structure at pH = 6). The reason for this result may be that SnS films prepared at different pH values have different deposition mechanisms, which results in different structures. The prepared SnS films are all smooth and well adhered. The optical bandgaps of the SnS films are determined to be 1.75 eV and 1.12 eV for zinc blende structure and orthorhombic structure, respectively.     

Electrical, photoelectrical, and photoelectrochemical properties of electrodeposited CdTe films subjected to high-energy irradiation

The general goal of this work is to study the structure and photoelectrical properties of the electrochemically deposited thin CdTe films. The conducted investigation has shown that (i) as-deposited films have the single-phase structure with a grain size of 1-10 μm and are of the n-type conductivity; (ii) photosensitivity abruptly decreases when the film thickness is over 10 μm; (iii) annealing at temperatures less than 500 °C improves the film quality with retention of the n-type conductivity; and (iv) photosensitivity of the films is not impaired under irradiation by 6 MeV electrons with a fluence of 5 × 10¹⁴ cm^− 2.     

Research of optical and structural properties in Cu/Ti multilayer films

The Cu/Ti multilayer (ML) films were deposited on Si(1 0 0) and Si(1 1 1) substrate with a series of pair layers with Vanguard sputtering system. The influences of periodic number and substrate structure on UV-reflectivity of Cu/Ti superlattice films were investigated carefully. The result shows that the Cu/Ti ML films have clear layer-structure. The ML films deposited on Si(1 0 0) and Si(1 1 1) have UV-reflectivity of about 90% and 67% at 200 nm, respectively, but they have lower soft X-ray reflectivity of about 1.9% at 13.04 nm in terms of wavelength, with near normal incidence of 5°. The transmission microscope image indicates that the fabricated Cu/Ti ML films have superlattice structure.     

Comparative study on the characteristics of network and continuous Ni films

Ni films were deposited on anodic aluminum oxide (AAO) and SiO₂/Si(100) substrates at 300 K by direct current magnetron sputtering with the oblique target. The film thickness was 80 nm, 160 nm and 260 nm. The films grown on AAO substrates have a network structure while those deposited on SiO₂/Si(100) substrates are continuous. The network film consists of granules and is formed by granule connection. The granule consists of many fine grains. The granule size increases with increasing film thickness. The 80 nm-thick network film has a honeycomb-like structure. The continuous films grow with a columnar structure and the transverse size of columnar grains increases with increasing film thickness. All the network films show a Ni(111) diffraction peak while the 160 nm- and 260 nm-thick continuous films exhibit the Ni(111) and Ni(200) diffraction peaks. The network films have higher coercivity and residual magnetization ratio compared with the continuous films. The coercivity and the residual magnetization ratio increase with increasing film thickness for the network films while they are almost independent of the film thickness for the continuous films. A temperature dependence of the resistance within 5-200 K reveals that the 80 nm-thick network Ni film exhibits markedly a minimal resistance at about 40 K. A logarithmic temperature dependence of the conductance is verified at temperatures below 40 K. The temperature coefficient of resistance is smallest for the 80 nm-thick network film and is largest for the 260 nm-thick continuous film.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Characterization and ozone-induced coloration of ZnxNi1 − xO thin films prepared by sol-gel method

Zn_xNi_1 − xO thin films were prepared by sol-gel spin coating method onto glass substrates in combination with annealing process. Effect of zinc content on the structural, optical and ozone-induced coloration properties of as-prepared films was investigated by X-ray diffraction, field emission-scanning electron microscope, atomic force microscopy and UV-VIS spectrophotometer, respectively. X-ray diffraction results reveal that the structures of all films are still cubic NiO structure. Average grain size of Zn_xNi_1 − xO film increases with increasing annealing temperature and its crystallization is strongly affected by Zn content. Coloration of the films was obtained after UV/ozone exposure due to a presence of ozone-induced hydroxyl groups. Significant enhancement of coloration efficiency of the films is achieved as content of Zn increases.     

Growth temperature dependent dielectric properties of BiFeO3 thin films deposited on silica glass substrates

We have studied the dependence of dielectric properties on the deposition temperature of BiFeO₃ thin films grown by the pulsed laser deposition technique. Thin films have been grown onto amorphous silica glass substrates with pre-patterned Au in-plane capacitor structures. It is shown that on the amorphous glass substrate, BiFeO₃ films with a near-bulk permittivity of 26 and coercive field of 80 kV/cm may be grown at a deposition temperature of about 600 °C and 1 Pa oxygen pressure. Low permittivity and higher coercive field of the films grown at the temperatures below and above 600 °C are associated with an increased amount of secondary phases. It is also shown that the deposition of BiFeO₃ at low temperature (i.e. 500 °C) and post deposition ex-situ annealing at elevated temperature (700 °C) increases the permittivity of a film. The applied bias and time dependence of capacitance of the films deposited at 700 °C and ex-situ annealed films are explained by the de-pinning of the ferroelectric domain-walls.     

Structural, optical, and electrical properties of tin sulfide thin films grown by spray pyrolysis

Tin sulfide (SnS) thin films have been prepared by spray pyrolysis (SP) technique using tin chloride and N, N-dimethylthiourea as precursor compounds. Thin films prepared at different temperatures have been characterized using several techniques. X-ray diffraction studies have shown that substrate temperature (T_s) affects the crystalline structure of the deposited material as well as the optoelectronic properties. The calculated optical band gap (E_g) value for films deposited at T_s = 320-396 °C was 1.70 eV (SnS). Additional phases of SnS₂ at 455 °C and SnO₂ at 488 °C were formed. The measured electrical resistivity value for SnS films was ∼ 1 × 10⁴ Ω-cm.     

Effects of Laser in situ annealing on crystal quality of NiSi film grown on Si(001) substrate

NiSi thin films grown on Si(001) substrates with a main crystal orientation of NiSi[200]//Si[001] were prepared and Raman spectroscopy was used to study effects of laser annealing on the NiSi thin films. Results show that the crystal quality of the NiSi films can be improved after laser annealing for 60 min at a laser power of 140 mW. We have shown that laser annealing can also be used to make structural phase transitions of NiSi domains under an annealing power of 480 mW for 10 min.     

Structural,electrical and photoluminescence properties of ZnO:Al network films grown on nanochannel Al2O3 substrates by direct current magnetron sputtering with an oblique target

ZnO:Al network films were grown on nanochannel Al₂O₃ substrates at 300 K by direct current magnetron sputtering with an oblique target. The film thicknesses are 60 nm, 160 nm and 190 nm. The holes of the network films diminish with increasing film thickness. For the 60-nm thick film, the network is formed by connecting grains. For the 160-nm and 190-nm thick films, however, the network is formed by connecting granules. The granules consist of many small grains. All the network films have a wurtzite structure. The 60-nm and 160-nm thick network films mainly have a [1 0 1] orientation in the film growth direction while the 190-nm thick network film grows with a random crystallographic orientation. A temperature dependence of the resistance within 160–300 K reveals that the network films exhibit a semiconducting behavior and their carrier transport mechanism is thermally activated band conduction. Room temperature photoluminescence spectra for wavelengths between 300 nm and 700 nm reveal a violet emission centered at 405 nm for the 60-nm thick network film and a blue emission centered at 470 nm for both the 160-nm and the 190-nm thick network films. Annealing decreases the resistivity of the network film.     

Structural,electrical and photoluminescence properties of ZnO:Al films grown on MgO(0 0 1) by direct current magnetron sputtering with the oblique target

ZnO:Al films were deposited on MgO(0 0 1) substrates at 300 K and 673 K by direct current magnetron sputtering with the oblique target. The Ar pressure was adjusted to 0.4 Pa and 1.2 Pa, respectively. All the films have a wurtzite structure and a c-axis orientation in the film growth direction. The films deposited at 300 K initially grow with thin columnar grains and subsequently grow with large granular grains on the thin columnar grains. However, the films grown at 673 K consist mainly of dense columnar grains perpendicular to the substrate surface. The ZnO:Al film deposited at 673 K and 0.4 Pa has the lowest resistivity, the highest free electron concentration and Hall's mobility. A temperature dependence of the resistivity within 5–300 K reveals that the films grown at 300 K exhibit a semiconducting behavior and those grown at 673 K show a metal–semiconductor transition. The carrier transport mechanism is Mott's variable range hopping in the temperature range below 90 K for all the films and thermally activated band conduction above 215 K for the films grown at 300 K. Room temperature photoluminescence spectra for wavelengths between 300 nm and 800 nm reveal mainly blue-green emissions centered at 452 nm, 475 nm and 515 nm.     

Phase stabilization and microstructural studies of lead lanthanum titanate thin films

Thin ferroelectric films of PLTx (Pb_1−xLa_xTi_1−x/4O₃) have been prepared by a sol-gel spin coating process. As deposited films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various concentrations of La (x = 0.04, 0.08 and 0.12) on ITO coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out on films annealed at temperatures (350, 450, 550 and 650 °C). Characterization of these films by X-ray diffraction shows that the films annealed at 650 °C exhibit tetragonal phase with perovskite structure. Atomic force microscope (AFM) images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Fourier transform infrared spectra (FTIR) studies of PLTx thin films (x = 0.08) deposited on Si substrates have been carried out to get more information about the phase stabilization.     

Femtosecond laser deposited zinc oxide film and its optical properties

Zinc oxide (ZnO) thin films have been grown on Si (100) substrates using a femto-second pulsed laser deposition (fsPLD) technique. The effects of substrate temperature and laser energy on the structural, surface morphological and optical properties of the films are discussed. The X-ray diffraction results show that the films are highly c-axis oriented when grown at 80 °C and (103)-oriented at 500 °C. In the laser energy range of 1.0 mJ-2.0 mJ, the c-axis orientation increases and the mean grain size decreases for the films deposited at 80 °C. The field emission scanning electron microscopy indicates that the films have a typical hexagonal structure. The optical transmissivity results show that the transmittance increases with the increasing substrate temperature. In addition, the photoluminescence spectra excited with 325 nm light at room temperature are studied. The structural properties of ZnO films grown using nanosecond (KrF) laser are also discussed.     

Infrared and ultraviolet-visible spectroscopic studies of plasma polymerized 1, 1, 3, 3 - tetramethoxypropane thin films

Plasma polymerized 1, 1, 3, 3-tetramethoxy-propane (PPTMP) thin films of different thicknesses were prepared through glow discharge of 1, 1, 3, 3-tetramethoxypropane using a capacitively coupled reactor. The scanning electron micrographs show that as-deposited PPTMP thin films are smooth, uniform and pinhole free. Infrared spectroscopic investigation indicates the formation of conjugation along with C = O bonds in as deposited PPTMP thin films. Apart from aliphatic conjugation of C = C and C = O bonds there is formation of C-O-C bond owing to rearrangement of oxygen due to heat treatment of PPTMP thin films. A red shift in the maximum absorption wavelength of the ultra violet-visible spectra for all the PPTMP thin films is observed compared to the monomer maximum absorption wavelength. The absorption coefficient, allowed direct transition, E_qd, allowed indirect transition and E_qi, energy gaps were determined. The E_qd and E_qi are found to be about 2.92 to 3.16 eV and 0.80 to 1.53 eV respectively, for as deposited PPTMP samples of different thicknesses. The E_qi of two samples of different thicknesses heat treated at 673 K for 1 hour is 0.55 and 0.65 eV .     

TiO2/Au/TiO2 multilayer thin films: Novel metal-based transparent conductors for electrochromic devices

Transparent conductors based on Au films, with thicknesses in the 2.6 < d < 9.8 nm range, were made by DC magnetron sputtering onto glass. The films went from an “island” structure at low thicknesses to a uniform structure at d > 8 nm, as seen from electron microscopy, electrical resistance, and spectrophotometric transmittance and reflectance. Optical data for uniform films were given a consistent interpretation within the Drude model. Optimized TiO₂/Au/TiO₂ films, with a luminous transmittance of 80%, were found to have good electrochemical durability and may be useful for applications in electrochromic devices.