Hopping conduction in Cr-doped amorphous gallium arsenide films

Amorphous Cr-doped GaAs has been prepared by rf sputtering and the dc conductivity measured at fields up to 10⁷ V/m and temperatures down to 80 K. The results are explained in terms of field-assisted hopping. Effects of isothermal annealing at temperatures up to 200°C are studied. The studies are repeated and the results compared with undoped a-GaAs. Room temperature resistivities of a-GaAs: Cr, a-GaAs and polycrystalline GaAs are also compared. The recrystallization temperature for a-GaAs films is determined to be between 320°C and 340°C.     

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.     

Influence of substrate temperature on the properties of vacuum evaporated InSb films

Indium Antimonide (InSb) thin films were grown onto well cleaned glass substrates at different substrate temperatures (303, 373 and 473 K) by vacuum evaporation. The elemental composition of the deposited InSb film was found to be 52.9% (In) and 47.1% (Sb). X‐ray diffraction studies confirm the polycrystallinity of the films and the films show preferential orientation along the (111) plane. The particle size (D), dislocation density (δ) and strain (ε) were evaluated. The particle size increases with the increase of substrate temperature, which was found to be in the range from 22.36 to 32.59 nm. In Laser Raman study, the presence of longitudinal mode (LO) confirms that the deposited films were having the crystalline nature. Raman peak located at 191.26 cm^–1 shift towards the lower frequencies and narrows with increase in deposition temperature. This indicates that the crystallinity is improved in the films deposited at higher substrate temperatures. Hall measurements indicate that the films were p‐type, having carrier concentration ≅10¹⁶ cm^–3 and mobility (4–7.7) ×10³ cm²/Vs. It is observed that the carrier concentration (N) decreases and the Hall mobility (μ) increases with the increase of substrate temperature. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structures of vapour-deposited amorphous films of arsenic chalcogenides

The structures of vapour-deposited amorphous films of composition As_xSe_1?x′, with x between 0 and 1, have been investigated by X-ray diffraction. In all cases the structure of the freshly deposited film differs very considerably from that of the corresponding bulk glass. For the elemental amorphous films the structure is highly disordered and contains voids which for Se cannot be annealed out below the crystallization temperature of 70°C or, for As, below the temperature ($\text{?130°}\text{C}$) where the As film re-evaporated. Annealing of the arsenic selenide films at temperatures below T_g causes the structures to relax towards those of the bulk, with a distribution of activation energies around 25 kJ mol^?1. The composition of the vapour has been examined by mass spectroscopy and it is concluded that even if some molecular identity is retained on condensation there must be considerable cross-linking to give the observed structural behaviour.     

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).     

The Investigation of Recrystallization Processes of Ni Films

Electron diffraction and resistance methods are used to study the recrystallization process in nickel films. Recovery process, initial, and secondary recrystallization are observed in films in annealing. Unlike bulk deformed materials the distortions in films are produced in the process of their evaporation. The duration and sequence of stages of recrystallization are determined by the temperature of substrate in obtaining films and by the temperature of subsequent annealing. At temperatures of substrate above 150°C the reflexes due to recrystallized grains are observed just after evaporation of films. Temperature intervals of initial and secondary recrystallization of nickel films are calculated at temperatures of substrate equal to 130°C and 200°C. Correlation between the width of diffraction line, depending on the degree of lattice distortions, electrical resistance, measured at temperature of annealing and the number of recrystallized grains is noted. For reasons given it can be concluded that electron scattering in films takes place in lattice distortions in the crystallite and in their boundaries. The results obtained are of great interest in choosing optimum conditions for preparing films with given characteristics.     

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)     

Influence of the VPE parameters on the epitaxial film properties for the (Pb1−xSnx)1+yTe1−y system

Epitaxial films have been produced for 0 ? x ? 1 by steps of 0.1. The growth rate, crystalline quality, carrier concentration and composition have been measured as a function of source, substrate and Te₂ source temperature. The growth rate is adjustable between 0.1 and 36 μm h^-1 and the films have smooth and shiny surfaces. The crystalline quality, conduction type and carrier concentration is mainly determined by the Te₂ pressure. It is possible to choose the type and the carrier concentration in the stable region for a source composition x ? 0.2. The films are always p-type if x ? 0.3. The composition of the films is varied by the source and by the substrate temperature. It is possible to vary the film composition compared to the source composition in the range of ±20% by varying the substrate temperature.     

Influence of substrate temperature on the properties of electron beam evaporated ZnSe films

ZnSe films were deposited on glass substrates keeping the substrate temperatures, at room temperature (RT), 75, 150 and 250 °C. The films have exhibited cubic structure oriented along the (111) direction. Both the crystallinity and the grain size increased with increasing deposition temperature. A very high value of absorption co‐efficient (10⁴ cm^‐1) is observed. The band gap values decrease from a value of 2.94 eV to 2.69 eV with increasing substrate temperature. The average refractive index value is in the range of 2.39 – 2.41 for the films deposited at different substrate temperatures. The conductivity values increases continuously with temperature. Laser Raman spectra showed peaks at 140.8 cm^‐1, 246.7 cm^‐1and 204.5 cm^‐1which are attributable to 2TA LO phonon and TO phonon respectively. (© 2010 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.     

Comparison of tin‐doped indium oxide films fabricated by spray pyrolysis and magnetron sputtering

A comparison of the properties between Tin‐doped Indium Oxide (ITO) films fabricated by sputtering and spray pyrolysis is presented. This analysis shows that the ITO films fabricated by DC magnetron sputtering in pure argon gas requires of a subsequent annealing for the improvement of their structural, electrical and optical properties, when they are compared to films fabricated by single‐stage spray pyrolysis process that includes a new approach. The optimum annealing temperature for ITO films sputtered at room temperature lies in the 300‐350 °C range. Under such conditions, the ITO sputtered films are slightly more resistive than the resistivity (2 × 10^‐4 Ω‐cm) shown by films sprayed at 480 °C using a solution with a 5 % of tin to indium ratio, and almost four times the worst value of the combination of transparency and conductivity determined by the value of the figure of merit (FOM). The sprayed films have a high value of the FOM, 2.9×10^‐2 Ω^‐1, which is comparable with the best published results.     

Structural,Morphological and Electrical Studies on Barium Strontium Titanate Thin Films Prepared by Sol‐Gel Technique

The crystal structure, surface morphology, compositional homogeneity and electrical properties of barium strontium titanate (BST) thin films are investigated. The films were deposited on bare silicon and platinum coated silicon substrates by spin coating process. The precursor solution with Ba/Sr ratio 70/30 was prepared by sol‐gel synthesis using metal alkoxides. The crystalline nature and morphology of the films are found to be strongly influenced by the heating cycle adopted to form the Ba_0.7Sr_0.3TiO₃ layer. The elemental composition analysis on the surface and in‐depth confirms the stoichiometry of the films. The dielectric constant at 100 kHz and dissipation factor at room temperature is found to be 120 and 0.0236 for the films with 400nm thickness annealed at 700°C for 2 hrs. The leakage current density of the film is found to be 4x10^‐8 A/cm² from I‐V measurements.     

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.     

The effects of oxygen,hydrogen and fluorine on the conductivity of high purity evaporated amorphous silicon films

Electron bombardment evaporation was used to deposit amorphous silicon (α-Si) films in an evaporator with a base pressure of 2 × 10^?10 Torr. Rutherford backscattering analysis was used to establish the conditions necessary for deposition of pure films.The DC conductivity was measured as a function of temperature (? 150°C to + 140°C). Pure films, which were deposited between room temperature and 400°C, were found to have a room temperature conductivity (σ_RT) in the region of 10^?3μ^?1cm^?1 and a log $\text{σα}\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ dependence. The value of σ_RT could be reduced by annealing reaching a minimum of 2 × 10^?7μ^?1 cm^?1 for an anneal temperature (T_A) of 520°C, but activated conduction was not observed.The implantation of hydrogen or fluorine (or contamination with oxygen) had the effect of reducing σ_RT, with a minimum value of less than 10^?8μ^?1cm^?1 (T_A = 400°C) for fluorine implantation to a dose of ≈ 10¹⁶ cm² (≈ 0.4 at% concentration). These films had high temperature (50°C) activation energies typical of activated conduction in extended states on the edge of the mobility gap. Implantation of fluorine to a dose of 1.5 × 10¹⁷ resulted in a rise of σ_RT (T_A = 400°C) to nearly 10⁴μ^?1 cm^?1 and log $\text{σα}\text{T}{}^{\mathrm{<mtext>?1</mtext><mtext>4</mtext>}}$ behaviour.X-ray analysis revealed that some crystallization occurred in films annealed at 600°C. This is correlated with a rise in σ_RT of the pure films and the disappearance of the effects of the introduced impurities.     

Conditions for single-crystal formation during bridgman growth

The microstructure of IV–VI crystals grown by varying the shape of the conical bottom of a ampoule, the melt superheating ΔT⁺ with respect to the liquidus temperature of a blend, the axial temperature gradient in a furnace ΔT, and the pulling rate of a ampoule v were studied. It was found that the nucleation of a single-crystal seed is most likely under the following conditions: ΔT ≤ 20 K/cm, ΔT⁺ < 30 K, and v < 0.4 mm/h. The conical bottom of a ampoule should have walls of constant thickness. The principle of geometric selection of a single-crystal seed is not efficient. The obtained results are discussed with regard to data on the structure and behavior of IV–VI melts upon heating and cooling.     

Growth of YBa2Cu3O7 films with [110] tilt of CuO planes to surface on SrTiO3 crystals

YBa₂Cu₃O₇ films with the CuO plane tilted to the surface have been grown on SrTiO₃ crystalline substrates by pulsed laser deposition. This tilt was obtained by rotating the film lattice with respect to the substrate surface around its [110] axis oriented parallel to the surface. The zero tilt of the CuO plane was implemented at the orientation of the SrTiO₃ crystal surface parallel to the (100) plane. The rotation angles were varied in the range from 0° to 70°. It is found that, being tilted at any angle, the CuO planes of the film remain parallel to one or several crystallographic planes of the (100)-type substrate. In the range of tilt angles from 0° to 49°, the film has a single-crystal structure. Above 49° the film is transformed into a three-domain texture and its surface roughness sharply increases.     

Studies on zirconium nitride films deposited by reactive magnetron sputtering

This paper deals with the preparation of Zirconium Nitride films by DC reactive magnetron sputtering. Films were deposited on silicon substrates at room temperature. Nitrogen partial pressure was varied from 4 × 10⁻⁵ to 10 × 10⁻⁵ m bar and the effect on the structural, electrical, optical properties of the films was systematically studied. The films formed at a nitrogen pressure of 6 × 10⁻⁵ mbar showed low electrical resistivity of 1.726 × 10⁻³ Ω.cm. The deposited films were found to be crystalline with refractive index and extinction coefficient 1.95 and 0.4352 respectively. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of YBa2Cu3O7 films with [100] tilt of CuO planes to the surface on SrTiO3 crystals

YBa₂Cu₃O₇ films with CuO planes tilted to the surface have been grown on SrTiO₃ crystals by pulsed laser deposition. The tilt angle was varied in the range from 0° (CuO planes are parallel to the surface) to 70°. At this tilt, the crystalline lattice of the film was rotated by rotating the substrate crystalline lattice around its axis [100], which is oriented parallel to the surface. The zero tilt of CuO planes corresponds to the orientation of the SrTiO₃ surface parallel to the (100) plane. It is established that the CuO planes of the film remain parallel to one or several (100)-type planes of the substrate at an arbitrary tilt angle. In the range of tilt angles from 0° to 41°, the film has a single-crystal structure. At tilt angles above 41°, the film is transformed into a two-domain texture and its surface roughness sharply increases.     

Metastable states in high carbon C–(Fe,Ni, Co) films obtained by three-electrode ion-plasma sputtering

Abstract

The effect of ion-plasma deposition on the structure of high-carbon films (at. %) Fe–(20–84) % С, Co–(5–52) % С, Ni–(7–61) % С was investigated. The lattice periods and crystallite sizes of nonequilibrium phases in the as-deposited state and after heating are determined. The temperatures of the beginning and end of the decay of metastable phases during heating at a constant speed are established. The transition from an amorphous to an equilibrium crystalline state in Fe–C films passes through the stage of formation and subsequent decomposition of an intermediate, metastable hcp phase of variable composition. The electrical and hysteretic magnetic properties of the films were measured in the as-deposited state and after heat treatment. The compositions and conditions for producing films with low values of the temperature coefficient of electrical resistance and high coercive force are established. Thus, high-carbon films of Ni–61% C in the as-depoteted state and Fe–69% C films after heating to 900?K are characterized by small TCR values (± 10^?6 К^?1) over a wide temperature range.     

The Process of Formation of Epitaxial Cadmium and Zinc Oxide Films by Interaction of Single-Crystal AIIBVI Layers with Oxygen

The results of electron microscopic and electron diffraction investigation of the surface during annealing of single-crystal A^IIB^VI (CdS, CdSe, ZnSe, ZnS) films in the presence of oxygen are reported. It is shown that the behaviour of islands of cadmium oxide formed by chemical interaction between O₂ and the CdS, CdSe substrate in the process of growth resembles that of the nuclei in film condensation. CdO films become “continuous” more quickly, if the size of blocks of substrate-epitaxial A^IIB^VI film is larger. Epitaxial ZnO films formed on the surface of epitaxial ZnS and ZnSe layers are of a wurtzite structure or a cubic structure with the parameter a = 4.5 Å.