Effect of some growth parameters on vacuum-deposited CulnSe2 films

P-type copper indoselenide (CulnSe₂) thin films were vacuum-deposited on glass substrates by a single-source thermal evaporation technique under different conditions of preparation. The structural properties of the films were investigated by X-ray diffraction and transmission electron microscopy and diffraction techniques. The dark resistivity of the deposited films was investigated as a function of film thickness, deposition rate and substrate temperature. The conductivity activation energy ranges from 0.851 to 1.01 eV depending on the deposition rate. Single-phase and stoichiometric CulnSe₂ films could be deposited at low deposition rates (less than 4 nms^–1). Higher deposition rates led to multiphase films containing InSe, ln₂Se₃, CuSe and Cu₃Se₂ in addition to CulnSe₂.     

Preparation of cobalt oxide films by plasma-enhanced metalorganic chemical vapour deposition

Co oxide films were prepared on glass substrates at 150–400°C by plasma-enhanced metalorganic chemical vapour deposition using cobalt (II) acetylacetonate as a source material. NaCl-type CoO films were formed at low O₂ flow rate of 7cm³ min^–1 and at a substrate temperature of 150–400°C. The CoO films possessed (100) orientation, independent of substrate temperature. Deposition rates of the CoO films were 40–47 nm min^–1. The CoO film deposited at 400 °C was composed of closely packed columnar grains and average diameter size at film surface was 60 nm. At high O₂ flow rate of 20–50 cm³ min^–1, high crystalline spinel-type Co₃O₄ films were formed at a substrate temperature of 150–400°C. The Co₃O₄ film deposited at 400°C possessed (100) preferred orientation and the film deposited at 150°C possessed (111) preferred orientation. Deposition rates of the Co₃O₄ films were 20–41 nm min^–1. Both Co₃O₄ films with (100) and (111) orientation had columnar structure. The shape and average size of the columnar grains at the film surface were different; a square shape and 35 nm for (100)-oriented Co₃O₄ film and a hexagonal shape and 60 nm for (111)-oriented film, respectively.     

Preparation and characterization of Y-system superconducting thin films by mist microwave-plasma chemical vapour deposition

Superconducting thin films of Y-Ba-Cu-O were prepared on single-crystal MgO (100) substrates by the mist microwave-plasma chemical vapour deposition (MPCVD) using an aqueous solution of metal nitrate. The growth rate was observed to be controlled by the concentration of metal nitrate in the solution. The X-ray diffraction patterns showed that the prepared films consisted of 123 phase with c-axis orientation perpendicular to the substrates. The dependence of T _c-zero (zero resistance) of films on the microwave power was investigated. In addition, the effect of the ozone on the preparation of films was investigated. The maximum T _c-zero (84 K) of as-deposited films was obtained at a metal concentration in the solution of 0.50 moll^–1, a microwave power of 300 W and an ozone concentration in oxygen gas of 3.0%.     

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10^–2–10^–1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca₂P₂O₇, Ca₂P₂O₉ and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.     

Superconducting characteristics and epitaxial-growth analyses of YBa2Cu3O7−x thin films by direct-current magnetron sputtering

Using direct-current magnetron sputtering deposition, we have successfully prepared highquality epitaxial YBa₂Cu₃O_7–x thin films, on (1 0 0) and (1 1 0) ZrO₂, SrTiO₃ and LaAlO₃ substrates. The films reached zero resistance at about 90 K and had a critical current density, J _c (at 77 K, H=O), above 10⁶ Acm^–2. Electrical measurements showed that the films had a small microwave surface resistance. The epitaxial structure of the films was studied by X-ray diffraction (XRD), Rutherford backscattering (RBS) and channeling spectroscopy, X-ray double-crystalline diffraction and transmission electron microscopy (TEM). It was found that the c-axis of the film grown on the (1 0 0) substrates under optimum deposition conditions was perpendicular to the substrate surface. But on the (1 1 0) substrates, epitaxial growth was along the (1 1 0) or (1 0 3) direction. The experimental results indicate that the films had excellent superconducting properties and complete epitaxial structure.     

Structural,electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique

A low cost chemical bath deposition (CBD) technique has been used for the preparation of Cu_2–xSe thin films on glass substrates. Structural, electrical and optical properties of these films were investigated. X-ray diffraction (XRD) study of the Cu_2–xSe films annealed at 523 K suggests a cubic structure with a lattice constant of 5.697 Å. Chemical composition was investigated by X-ray photoelectron spectroscopy (XPS). It reveals that absorbed oxygen in the film decreases remarkably on annealing above 423 K. The Cu/Se ratio was observed to be the same in as-deposited and annealed films. Both as-deposited and annealed films show very low resistivity in the range of (0.04–0.15) × 10^–5 -m. Transmittance and Reflectance were found in the range of 5–50% and 2–20% respectively. Optical absorption of the films results from free carrier absorption in the near infrared region with absorption coefficient of 10⁸ m^–1. The band gap for direct transition, E_g.dir varies in the range of 2.0–2.3 eV and that for indirect transition E_g.indir is in the range of 1.25–1.5 eV.     

Microstructure of vacuum-deposited tin thin films

Tin thin films of equal thickness were vacuum deposited on NaCl substrates at different deposition rates both in high vacuum (2×10^–5 Torr) and poor vacuum (1×10^–3 Torr). These films were examined by electron microscopy and the grain size and density in the films were determined. It was found that both in poor and high vacuum, as the deposition rate was increased the grain size decreased and grain density increased. However, the deposition rate must be increased by an order of magnitude in order to observe large changes in the grain size and density. It was also observed that the films prepared in poor vacuum, especially at low deposition rates, consist of islands with jagged edges. These observations have been interpreted on the basis of nucleation theory and the effect of adsorbed/chemisorbed gases on island growth in these films.     

Structural, optical and photoelectrochemical properties of brush plated CdSe x Te1 − x thin films

CdSe _x Te_{1 – x} films have been deposited by the brush plating technique for the first time, on titanium and conducting glass substrates at room temperature. These films were annealed in argon atmosphere at 475°C for 15 min. Their structural, optical and photoelectrochemical (PEC) properties are presented and discussed. The power conversion efficiency has been found to be 9.0% at 60 mW cm^–2white light illumination. A peak quantum efficiency of 0.7 has been obtained for the films of composition CdSe_0.7Te_0.3. Donor concentration of 10¹⁷cm^–3and electron mobility of 60 cm²V^–1sec^–1were obtained.     

Sputtered rutile stoichiometric TiO2 nanocrystalline films

Titanium dioxide (TiO₂) films were prepared at room temperature on silicon and glass substrates using DC reactive magnetron sputtering at the rate of 0.1 nms⁻¹ from a pure metal Ti target. X-ray diffraction (XRD) studies on freshly prepared samples showed a purely rutile phase. It is found from AFM that annealing of fresh TiO₂ films at 550°C for 30 min produced an increase in grain size by a factor of at least 1.5. X-ray photoelectron spectroscopies (XPS) gives correct ratio for purely TiO₂ stoichiometry. Optical band gap was estimated to be 3.2 eV from UV–vis transmission spectra.     

Preferred orientation of AlN plates prepared by chemical vapour deposition of AlCl3 + NH3 system

Aluminium nitride (AlN) plates about 1 mm thick (maximum) were prepared by chemical vapour deposition (CVD) at the maximum deposition rate of 430 nm s⁻¹ using AlCl₃, NH₃ and H₂ gases at deposition temperatures,T _dep, of 873–1473 K. The effects of deposition conditions on the preferred orientation, morphology and micro-structure were investigated. WhenT _dep was less than 1073 K, the resulting CVD AlN plates contained some impurity chlorine and the aluminium content exceed the nitrogen content. WhenT _dep exceeded 1173 K, no chlorine was detected, and the Al/N atomic ratio matched the stoichiometric value. The lattice parameters (a=0.311 nm,c=0.4979 nm) and density (3.26×10³ kgm⁻³) were in agreement with values reported previously. The crystal planes oriented parallel to the substrates changed from (1 1 ˉ2 0) to (1 0 ˉ1 0) to (0001) with increasing total gas pressure (P _tot) and decreasingT _dep. This tendency is discussed thermodynamically and is explained by the change of supersaturation in the gas phase.     

Influence of different process parameters on physical properties of fluorine dopes indium oxide thin films

Fluorine-doped indium oxide films were prepared by the spray pyrolysis technique. The physical properties of these films were investigated with respect to various process parameters, namely variation of dopant concentration (in the solution), deposition temperature (T _s), carrier gas (air) flow rate and the thickness of the film. The best films had a Hall mobility of the order of 28 cm²V^–1 s^–1 and a carrier density of 2.7 × 10²⁰ cm^–3. These films were deposited at T _s=425 °C at an air flow rate of 71 min^–1 for an atomic ratio of fluorine to indium of 72%. The electrical resistivity of these films was of the order of 10^–4 cm and the average transmission in the visible range was found to be 80–90%. The films were polycrystalline, n-type semiconductors with [400] as a preferred orientation. The preferred orientation changes from [400] to [222] depending upon the process parameters.     

Growth and Characterization of PrBa2Cu3O7?x Thin Film Used as Template Layer on SrTiO3 Substrate

We have grown PrBa₂Cu³O_7–x (PBCO) thin films on (100) SrTiO₃ substrates using pulsed laser deposition (PLD). X-ray diffraction (XRD) studies indicate that the orientation of PBCO films varied with increasing deposition temperature: b axis oriented films can be grown at 680°C, and a axis oriented films at the temperature between 692°C and 705°C. Atomic force microscopy (AFM) reveals that a good flatness of the films was obtained with surface mean roughness of less than 24 Å, indicating that it is suitable for use as template layers in a axis oriented epitaxial YBa₂Cu₃O_7–y /PBCO and YBCO/tetragonal–YBCO/PBCO multilayer structures.     

Electrical and optical properties of vacuum-evaporated CdS films

1 m CdS films for the window layer of CdS/CulnSe₂ solar cells have been prepared by vacuum evaporation at various deposition conditions. Deposition rates were 0.73 and 3.3 nms^–1, and substrate temperature ranged from 50 to 225 C. The effect of the deposition conditions on the properties of CdS films was investigated by measuring electrical resistivity, optical transmittance and reflectance.The resistivity of the evaporated CdS films strongly decreased as substrate temperature decreased and the films with high deposition rate showed lower resistivity compared to the films with low deposition rate. Interestingly, the combination of high deposition rate and very low substrate temperature resulted in an increase of resistivity. The optical transmittance of CdS films increased as substrate temperature decreased and then decreased with further decrease in substrate temperature. The transmittance strongly depended on deposition rate at low substrate temperature (<100C), while it was independent of deposition rate at high substrate temperature (>100C). In particular, high transmittance can be extended to lower substrate temperature by reducing deposition rate. Low optical reflectance can be obtained by lowering substrate temperature. The results indicate that CdS films of low resistivity and high transmittance can be produced by vacuum evaporation at low substrate temperature and low deposition rate.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Density and deposition rate of chemical-vapour-deposited boron nitride

A study is made on the density and deposition rate characteristics of chemical-vapour-deposited boron nitride (CVD-BN) plates synthesized by use of the BCl₃-NH₃-H₂ system at a deposition temperature (T _dep) of 1200 to 2000°C and a total gas pressure (P _tot) of 5 to 60 torr. At aP _tot of 5 torr, all the CVD-BN plates synthesized at eachT _dep above 1300°C had a density greater than 2.O g cm^–3, and thus showed no noticeable dependence onT _dep. Over theP _tot range from 10 to 60 torr. on the other hand, the density of the plates reached the maximum of 2.08g cm^–3 at aT _dep of 2000° C. AsT _dep was lowered, the density decreased down to a minimum of 1.40 g cm^–3 The deposition rate varied with bothT _dep andP _tot and showed a maximum value under a certainP _tot at a givenT _dep. The value ofP _tot where the deposition rate becomes maximum changed depending on theT _dep. The maximum deposition rate was 0.6 mm h^–1 for the CVD-BN plates when the density was less than 2.0 g cm^–3, and 0.4 mm h^–1 when the density was above 2.0 g cm^–3 The effects of deposition conditions on the characteristics of density and deposition rate are discussed in terms of the structure and deposition mechanism.     

Optimizing indium tin oxide thin films with bipolar d.c.-pulsed magnetron sputtering for electrochromic device applications

In this paper, indium tin oxide (ITO) films were prepared by bipolar d.c.-pulsed magnetron sputtering in a mixture of argon and oxygen onto unheated glass substrates. A target of ITO with 10 weight percent (wt %) tin was used. The influences of ratios of t^– _on/t⁺ _on (negative pulse-on time/positive pulse-on time) on the optical, electrical, and structural properties of ITO films have been investigated. The correlations between the deposition parameters and the film properties were discussed. An optimal condition based on reactive bipolar d.c.-pulsed sputtering for obtaining high transmittance, low resistivity, and low surface roughness of ITO films with high deposition rate is suggested. Then, ITO films grown at room temperature by bipolar d.c.-pulsed sputtering were used to form electrochromic devices of WO₃. Better electrochromic performances were found in comparison to those measured with commercially available ITO films on glass substrates.     

Atomic layer deposition of HfO2 thin films and nanolayered HfO2–Al2O3–Nb2O5 dielectrics

Smooth, 4–6-nm thick hafnium oxide films were grown by atomic layer deposition from HfI₄ or HfCl₄ and H₂O on SiO₂/Si(1 0 0) substrates at 300 °C. Non-uniform films were obtained on hydrogen-terminated Si(1 0 0). The stoichiometry of the films corresponded to that of HfO₂. The films contained small amounts of residual chlorine and iodine. The films deposited on SiO₂/Si(1 0 0) were amorphous, but crystallized upon annealing at 1000 °C. In order to decrease the conductivity, the HfO₂ films were mixed with Al₂O₃, and to increase the capacitance, the films were mixed with Nb₂O₅. The capacitance–voltage curves of the Hf–Al–O mixture films showed hysteresis. The capacitance–voltage curves of HfO₂ films and mixtures of Hf–Al–Nb–O were hysteresis free.     

Morphology and structure of tantalum oxide deposit prepared by KrF excimer laser CVD

Tantalum oxide films have been deposited on substrates by decomposing Ta(OCH₃)₅ photolytically in the beam of a KrF excimer laser under various conditions of laser fluence (200–450 J m^–2), repetition rate (20–120 Hz), supply rate of Ta(OCH₃)₅ (50–400 mg h^–1) and substrate temperature (403–723 K). The deposits were highly oriented when produced at laser fluences of 350 and 450 J m^–2. Their XRD patterns suggested the formation of -Ta₂O₅. The (1 1 1 0) planes were preferentially oriented parallel to the substrate surface when produced at lower repetition rates, higher supply rates of Ta(OCH₃)₅, and lower substrate temperatures; whereas (1 1 1 1) planes were similarly oriented when the conditions were reversed. The preferred orientation may be explained in terms of supersaturation. The deposits produced at a fluence of 200 J m^–2 were, however, rather amorphous.     

Electrical, optical and structural characterization of high-k dielectric ZrO2 thin films deposited by the pyrosol technique

High-k dielectric zirconium oxide (ZrO₂) thin films have been deposited on silicon substrates at temperatures from 400 to 600 °C using the spray pyrolysis technique. The films were deposited from two spraying solution concentrations (0.033 and 0.066 M) of zirconium acetylacetonate dissolved in N,N-dimethylformamide. These films were stoichiometric, transparent and with a very low surface roughness (5–40 ). The refractive index of these films was of the order of that obtained for a bulk material (2.12). Films deposited with high molar concentration presented the best electrical characteristic, have a dielectric constant in the range 12.5–17.5, depending on the deposition temperature, and can stand electric fields up to 3 MV cm^–1 without observing destructive dielectric breakdown. Transmission electron microscopy measurements, indicate that the films consist of nano-crystallites of the tetragonal ZrO₂ crystalline phase embedded into an amorphous matrix. Infrared spectroscopy measurements of the films show peaks associated with ZrO₂ and a peak related to silicon dioxide (SiO₂). The analysis of spectroscopic ellipsometry measurements on these films indicates the existence of a layer at the ZrO₂/Si interface composed of SiO₂ as well as ZrO₂ and crystalline silicon.     

Growth of oriented aluminium nitride films on silicon by chemical vapour deposition

Aluminium nitride films were grown on silicon substrates using the chemical vapour deposition (CVD) method. The properties of the films were studied by scanning electron microscopy (SEM), atomic force microscope (AFM) measurements, X-ray diffraction and Raman scattering. The resulting films were strongly textured and had a preferential orientation with the c-axis normal to the surface, the Raman spectra showed two peaks at 607 and 653 cm^–1 and two large bands at 750 and 900 cm^–1 of smaller intensity. Both the macro- and micro-Raman spectra showed the same peaks.