Preparation and characterization of radio-frequency-sputtered Ba2Si2TiO8 thin films

Radio-frequency-sputtered barium titanium silicate (BST, Ba₂Si₂TiO₈) thin films were grown on crystalline Si (100) substrates and were characterized using wavelength-dispersive spectrometry (WDS), X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), and diagonal techniques for dielectric properties. The chemical compositions of the films increasingly deviated from stoichiometry with film thickness. At the initial stage of deposition the grain configuration is dependent on the Si substrate texture. XRD analysis indicates that the BST films deposited at an optimum substrate temperature of 845 °C were strongly c-axis oriented, and that the film orientation is manipulated by substrate temperature and supersaturation. The corresponding film-growth rate in the direction normal to the film surface at 845 °C was 1.95 nm min^–1 at the initial stage, and decreased with sputtering time. The as-deposited films have a room-temperature bulk resistivity of 1.8 ×10⁷ m in the direction of thickness and an isotropic surface resistivity of 1.5×10³ m. The high-frequency relative dielectric constant, 0.05 at frequencies higher than 9 MHz, is lower than that of many typical piezoelectric materials. The high-frequency impedance character is typical of piezoelectric materials, giving a minimum impedance frequency of 9.0 MHz and a serial resonant frequency at about 9.5 MHz.     

Pyrosol deposition of fluorine-doped tin dioxide thin films

Fluorine-doped tin dioxide (SnO₂F) films were deposited from a tin tetrachloride solution in methanol utilizing a pyrosol deposition process. It is shown from thermodynamic calculations that the atmosphere during deposition is oxygen-rich and also suggested that chlorine and hydrogen chloride, which are produced during the deposition reaction, influence crystal growth. Detailed electrical, optical and structural properties of the material with respect to varying film thickness and substrate temperature are presented and discussed. Resistivity of the films deposited at 450 °C decreased from 6×10^–4 to 2×10^–4 cm, while the mobility increased from 14 to 45 cm²V^–1s^–1, respectively, when the film thickness was varied from 100 to 1650 nm. The carrier concentration was relatively unchanged for film thicknesses higher than 200 nm. Optimized SnO₂F films (600 nm) having a resistivity of 6×10^–4 cm, a carrier mobility of 20 cm²V^–1s^–1, a carrier concentration of 8×10²⁰ cm^–3 and a transmittance in excess of 80% are quite suitable as electrodes for amorphous silicon solar cells.     

Properties of transparent conducting ZnO : Al oxide thin films and their application for molecular organic light-emitting diodes

ZnO : Al (ZAO) films were deposited on glass substrates by a reactive mid-frequency sputtering system. The microstructural, electrical, and optical properties of ZAO films were investigated. It was observed that the polycrystalline film was (0 0 2n) textured with columnar structure. The minimum resistivity was 1.39×10^–4 cm with a carrier concentration of 1.58×10²¹ cm^–3 and a Hall mobility of 28.2 cm² V^–1 s^–1, correspondingly with the c-axis nearly equal to the value of ZnO powder and the minimum mechanical stress therein. The average transmittance of 80.8% in the visible range and infrared reflectance of over 86% in the 1600–4400 cm^–1 interval were obtained. The ZAO films were used as the transparent anodes to fabricate light-emitting diodes, and a luminance efficiency of 2.09 cd A^–1 was measured at a current density of 5.38 A m^–2.     

Electrical and structural characterization of DLC films deposited by magnetron sputtering

In this work diamond-like carbon (DLC) films were deposited by d.c. magnetron sputtering using a graphite target and argon as the discharge gas. Hydrogen gas was introduced in the discharge chamber to produce hydrogenated DLC films. By increasing the hydrogen flow from zero to 22% of the total flow, the following modifications of the film properties were observed: a decrease in the r.m.s. roughness (from 0.45 to 0.21 nm); an increase in the electrical resistivity (from 5×10⁶cm to 2.55×10⁸cm , while the relative dielectric constant remained almost constant at about 3.3. Increasing the substrate temperature, we observed a logarithmic decrease of the electrical resistivity of the films, caused by a self-annealing process of the DLC film during the deposition. This decrease was faster for the hydrogenated films, due to the additional effect of the dehydrogenation. The Raman spectra analyses of these films are in agreement with these observations.     

Preparation of Au-paste by liquid-phase reaction

Preparation of Au-paste by sol-gel-like reactions from the liquid phase was investigated. The Au-paste thus obtained was a well dispersed colloidal gold. The films sintered from the paste were good metallic conductors. These films showed good resistivity despite the presence of included metal oxides such as titania or zirconia in the matrix. The resistivity of the films thus obtained is about 3.0×10^–7m, which is not so different from that of pure gold (2.35 ×10^–8m).     

Synthesis and properties of CeN thin films deposited by arc ion plating

Cerium nitride films were deposited by ion plating in an electron-beam sustained Ce arc discharge in a nitrogen atmosphere. The crystal structure was strongly affected by the arc discharge current and the substrate temperature. The lattice spacing of CeN film is 0.5020 nm with a density of 7.82 g cm^–3. This film showed a paramagnetic property at 10 K in a magnetic field of 20 kOe. The Knoop hardness for CeN film is over 1600. The electrical resistivity was 4.6 × 10^–4 cm with p-type conductivity. The carrier concentration of the CeN film increased after exposure to the air, which suggested that the valence of Ce in CeN is probably 4+.     

Frequency and temperature dependencies of a.c. conductivity of polyvinyl alcohol (PVA)-CoCl2 composites

The a.c. conductivity for polyvinyl alcohol (PVA)-CoCl₂ composites prepared by a casting method has been measured at different frequencies (0.1–10 kHz) in the temperature range 300–450 K. At constant temperature, the frequency dependence of a.c. conductivity, (), was found to fit the established equation () = A ^s quite well. On the other hand, the temperature dependence of a.c. conductivity suggested an electronic hopping conduction mechanism in a thermally assisted electric field. Various theoretical mechanisms have been discussed to clarify the conduction processes in these samples. The correlated barrier hopping (CBH) mechanism, proposed by Elliott, was found to be the most appropriate one.     

Characterization and photovoltaic device application of dip-coated and rapid thermal annealed CdS films

The structure, composition, electronic and optical properties of dip-coated CdS in the as-deposited condition and following rapid thermal annealing have been investigated. It has been shown that oxygen incorporated in the CdS film can be leached out following rapid thermal annealing. Strongly oriented CdS films with resistivity = 0.16 cm and free electron concentration = 2.65 × 10¹⁷ cm^–3 have been grown. Thin film heterojunction devices fabricated by non-aqueous electrodeposition of CdTe on a glass-ITO-CdS cathode have been shown to exhibit good rectification behaviour and photovoltaic activity.     

Thickness dependence of electrical properties in thin films of undoped indium oxide prepared by ion-beam sputtering

Preparation and electrical characterization of undoped indium oxide films were examined as a function of thickness and annealing. Thin films ranging from 1.1 to 113 nm thickness were deposited on glass substrates by ion-beam sputtering. Low-angle X-ray diffraction analysis in multi-layered films showed the possibility that physically continuous and almost flat films were formed even in the thinnest 1.1 nm films. Room temperature resistivity of as-deposited films decreased sharply by more than five orders of magnitude as the thickness increased from 1.1 to 5.2 nm. The 2.4 nm thick films, in its as-deposited state, showed a gradual resistivity modulation with the change of atmosphere between air and argon gas at room temperature. Annealing at 300° C for 5 h in air increased the resistivity drastically; the room temperature resistivity of 24.3 nm thick films changed from 2.2×10^–3 cm (as-deposited) to higher than 10⁵ cm (annealed).     

Ionic conductivity of synthetic analcime,sodalite and offretite

The ionic conductivity of pressed pellets of dehydrated synthetic analcime, sodalite and offretite was determined by a.c. measurements within the range 10 Hz to 10 MHz. The ionic conductivity values of those zeolites exchanged with various monovalent cations were determined by the complex impedance plane method. The conduction activation energies range between 63 and 101 kJ mol^–1. Sodium analcime shows the best ionic conductivity, namely 1.8×10^–4–1 cm^–1 at 400° C. A comparison with the conductivity of other ion-conducting solids was made.     

Preparation of p-type GaAs layers for ohmic contact

The open-tube diffusion of zinc is used for the preparation of p-type layers in gallium arsenide. The process provides the capability of forming reproducible deep diffusions (0.4–2 m) over short diffusion times and in the temperature range 600–650 C. TiPdAu contacts are prepared on these layers. Using cw laser annealing we have obtained specific contact resistance 6.5 × 10^–7cm².     

Microstructural study of Au-Pd-Zn ohmic contacts to p-type InGaAsP-InP

A detailed microstructural study has been done on Au-Pd-Zn ohmic contacts to p-type InGaAsP epitaxially grown on InP. The doping level in the InGaAsP was 1.0 × 10¹⁹ to 1.5 × 10¹⁹ cm^–3 near the surface with the Zn concentration graded to a value of 7 × 10¹⁸ cm^–3 at the InGaAsP-InP interface. Metal layers (10 nm Pd,3 nmZn, 25 nm Pd and 50 nm Au) were deposited sequentially by electron beam evaporation. Contact resistances less than 10^–4 cm² were achieved for all annealing temperatures studied (380–440 C) and a minimum contact resistance of 2 × 10^–6 cm² was obtained for an anneal at 400 C for 20 s. Comparisons were made to similar metallizations on p-type InP. Lower contact resistances were achieved for the quaternary material compared with the binary material, however, contact stability and uniformity were worse.     

Properties of indium oxide/tin oxide multilayered films prepared by ion-beam sputtering

The preparation and characterization of indium oxide (InO _x )/tin oxide (SnO _y ) multilayered films deposited by ion-beam sputtering are described and compared with indium tin oxide (ITO) films. The structure and the optoelectrical properties of the films are studied in relation to the layered structures and the post-deposition annealing. Low-angle X-ray diffraction analysis showed that most films retained the regular layered structures even after annealing at 500° C for 16 h. As an example, we obtained a resistivity of 6×10^–4 cm and a transparency of about 85% in the visible range at a thickness of 110 nm in a multilayered film of InO _x (2.0 nm)/SnO _y (0.2 nm)×50 pairs when annealed at 300° C for 0.5 h in air. Hall coefficient measurements showed that this film had a mobility of 17 cm² V^–1 sec^–1 and a carrier concentration (electron density) of 5×10²⁰ cm^–3.     

Growth and Properties of V-Doped CdxHg1 – xTe Crystals

Cd _x Hg_{1 – x} TeV (x= 0.9–0.95) crystals were prepared by two versions of Bridgman growth, and their optical homogeneity and transport properties were studied. The electrical resistivity of the crystals was 10⁴to 10⁸ m. From the temperature dependences of the Hall coefficient, the activation energy of the vanadium level in Cd _x Hg_{1 – x} TeV was determined to be 0.73–0.82 eV.     

Simultaneous Double-Sided Deposition of Large Size HTSC Thin Films

An apparatus for simultaneous deposition of large size double-sided YBCO thin films by sputtering from single inverted cyclindrical target was constructed. Double-sided YBCO thin films on LaAlO₃ (100) substrate up to 30 mm in diameter were prepared to test the performance of the apparatus. The microwave surface resistance, R _s (77 K, 10 GHz, 0 T), of the YBCO thin films on both sides of the wafer ranged from 500 to 800 . Values of R _s (75 K, 145 GHz, 0 T) below 60 m were reached over the area of 20 mm × 15 mm on the wafer. The majority of the wafer area given in percent has R _s (75 K, 145 GHz, 0 T) values in the range of 21.5– 45.5 m. Lateral homogeneity of R _s values in the whole wafer was good enough to well meet the microwave application.     

Thin and superthin photoconductive CdSe films deposited at room substrate temperature

Low conductive and photosensitive CdSe films were deposited on substrates at room temperature. X-ray diffraction spectra showed a microcrystalline cubic structure for film thicknesses greater than 20 nm and an amorphous structure for film thicknesses below 10 nm. An optical band gap, E _g ⁰ , of 1.6 eV was determined using the Tauc-dependence usually employed for amorphous semiconductors. The dark conductivity, , of 10^{–9 –1} cm^–1 was measured in the as-deposited state, but an increase of five orders of magnitude was observed after heating the layer above 450 K. High photosensitivity was observed under illumination with white light as well as with monochromatic light over a wide spectral region (400–750 nm). A conclusion is reached concerning the existence of compensated donor and acceptor defects in the as-deposited state.     

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.     

The optical properties and a.c. conductivity of magnesium phosphate glasses

Magnesium phosphate [X MgO-(100–X) P₂O₅] glasses in the composition range [X=20, 25, 30, 40, 45, 50 mol %] have been made. The optical properties and a.c. conductivities were measured and their amorphous nature confirmed by X-ray diffraction technique. The variation of relative density with x was anomalous. In the ultraviolet/visible regions it was found that the fundamental absorption edge is a function of glass compositions and lower absorption coefficients, () follow the so-called Urbach edge. At lower absorption levels (1<<10⁴cm^–1), the width of the tail of localized states in the band gap, E _g, did not vary significantly with glass composition and lay in the range (0.26–0.343) eV. In the high absorption region (()>10⁴ cm^–1), the behaviour of () suggests that there are two different transition energies for electrons in k-space, namely direct allowed transitions and non-direct transitions. In the infrared region at wavelengths =2.5–30 m, the transmission spectrum has four absorption bands. Using the Kramers-Kronig theory, the optical constants (refractive index n and extinction coefficient k) have been determined from the transmission spectrum. The a.c. conductivity, (), real and imaginary dielectric constants, ₁, ₂, and loss factor, tan , have been determined at room temperature in the frequency region, = 2×10⁴–10⁶ Hz. It has previously been established theoretically that () ^s and s was found to be in the range 0.64–0.73, depending on glass composition.     

Amorphous indium tungsten oxide films prepared by DC magnetron sputtering

Indium-tungsten-oxide (IWO) films were prepared by dc magnetron sputtering at ambient substrate temperature (T_s). Characteristics of the films were compared with those of In₂O₃–SnO₂ (ITO) thin films prepared under the same condition. The sputter-deposited IWO films have entirely amorphous structure with an average transmittance of over 85% in the visible range and exhibit a minimum resistivity of 3.2 × 10^–4cm at W content [W/(In + W)] of 0.57 at.%. An in-situ heating X-ray diffraction measurement have shown that the crystallization temperature of IWO films is higher than those of ITO films (150–160C) and increases with increasing W content. This enabled a smooth amorphous surface of IWO films as compared with a rough surface of partially crystallized ITO films as revealed by an atomic force microscopy. IWO films are useful for transparent electrode of organic light emitting diode and polymer LCDs because of the low resistivity, high transparency and smooth surface obtainable by the conventional dc magnetron sputtering at room temperature.     

Kinetics of dissolution of silicon in CrO3-HF-H2O solutions

Silicon wafers [p-type, B-doped, 10 cm, dislocation density <500cm^–2, orientation (111)] have been dissolved in CrO₃-HF-H₂O solutions (Sirtl etch) with molar concentration ratios [Cr⁶⁺]/[HF] between 0.03 and 0.72 at temperatures between 10 and 60° C. The dissolution kinetics suggests that silicon suboxides SiO _x (0.67<×<1) are formed, and/or that the rate of diffusion of chromium is three times that of hydrofluoric acid.