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This paper reports the charge transport mechanism at low temperatures in (110) oriented polycrystalline tin oxide (SnO 2 ) films of less than 100 nm thickness prepared by reactive sputtering in the substrate temperature (T S ) range of 350–450 °C. Undoped tin oxide films with high electrical conductivity of 11 Ω –1 cm –1 have been achieved at 350 °C. The Hall mobility increases from 6.7 to 13.9 cm 2 /V·s and carrier concentration decreases from 11 × 10 18 to 0.9 × 10 18 cm –3 as T S is increased. In the 300–100 K temperature range we found two types of conduction mechanisms: thermally activated conduction till 160 K and nearest-neighbour-hopping conduction below 160 K. At temperatures below 90 K, the Mott variable-range-hopping (VRH) conduction governs the charge transport. In all the three regimes the activation energies of conduction increase with an increase in T S , being 15–50, 0.2–9, and 2–6 meV respectively, consistent with a decrease in oxygen vacancies at higher T S . The analysis of the data in Mott VRH conduction regime suggests a systematic localization of the oxygen vacancy states with an increase in growth temperature. Even at 70 nm thickness the films behave as three dimensional with regard to the Mott VRH conduction process.

Thin films of Cu–Co have been electrochemically deposited onto Cu-coated alumina substrates in a single sulfate bath. Electrochemical process parameters are expected to influence the chemical composition and microstructure and hence, physical properties of the films. We have attempted to study and understand the effect of various electrochemical process parameters like bath composition, bath temperature, deposition current density and pH of the electrolyte, along with annealing temperature and time on the magnitude of GMR in Cu–Co films. The maximization of GMR is understood in terms of an optimum distribution of the size and the separation of the magnetic particles via the thermally-induced phase segregation.

Epitaxial thin films of YBa 2 Cu 3 O 7– δ (YBCO) have successfully been grown by reactive RF-magnetron sputtering technique at a low pressure (0.95 mTorr) with T C ( R =0)=85.3 K and J C mag (4.2 K)≈2×10 7 A/cm 2 . The incorporation of oxygen in the as-grown films has been controlled by using different ambient—oxygen, air and argon—during in situ cooling. The superconducting behavior of the resulting films was studied using resistance–temperature and low field a.c.-susceptibility measurements and correlated with their structure. All the films exhibited metallic conduction in the normal state. The oxygen- and air-cooled films were superconducting, and exhibited usual orthorhombic structure, but the argon-cooled films were non-superconducting and possessed tetragonal structure. This implied that the structure of the film during deposition is tetragonal, and transforms to either of the oxygen rich orthorhombic-I or -II phases depending upon the oxygen/air ambient. The ‘ δ ’ values of 0.14, 0.32 and 0.70 and higher ‘ c ’-parameters of 1.1785, 1.180 and 1.183 nm have been obtained for oxygen-, air- and argon-cooled films, respectively.

In-situ superconducting c-axis oriented YBa2Cu307_s (YBCO) thin films have been grown at T sub = 775 °C on SrTiO3(100) and MgO(lOO) by r.f.-magnetro n sputtering at an oxygen partial pressure, which not only lies below the stability line but is more than an order of magnitude lower than its empirically suggested limit. The effect of variation in partial pressure of oxygen (POl) on the film characteristics is analyzed by employing a.c.-magnetic susceptibility, resistance-temperature variation, Rutherford backscattering, atomic force microscopy (AFM), scanning electron microscopy and X-ray diffraction techniques. The oxygen deficiency, 5, is calculated employing a number of techniques. The higher c-axis lattice parameters of the films are supportive of antisite disorder in the cations. The AFM investigations have established that Stranski-Krastanov-type growth mechanism is operative in the present case. The variation in critical current density (J™g(T)) with temperature is reported for the first time in the low pressure sputtered films exhibiting a J craas(43 K) of «4.6X 106 A cm" 2.

Thin films of amorphous (a-) Ge20Se80 − xBix (x = 4,10) and a-As2Se3 − xBix (x = 0.2, 0.5) have been prepared by thermal evaporation and characterized for their electrical and optical properties. The addition of bismuth, in excess of 4 at.%, to p-type a-Ge20Se80 and a-As2Se3 films results in large (several orders of magnitude) changes in the electrical conductivity and conversion of the conductivity from p to n type. A correlation of the electrical and optical data of the modified films suggests that the addition of bismuth causes a Fermi level shift and the electrical transport is predominantly due to hopping of electrons after being excited into localized states the conduction band edge.

Amorphous silicon-germanium (a-Si 1− x Ge x ) thin films have been prepared co-sputtering a composite target of high purity crystalline silicon (c-Si) and c-Ge using ion beam sputtering technique. The desired composition has been obtained by suitably adjusting the exposed areas of c-Si and c-Ge. The electrical, optical and structural properties of these films have been investigated as functions of composition (for a-Si 1- x Ge x ) and ion beam energy-voltage and substrate temperature (for a-Si 50 Ge 50 ). The amorphous silicon-germanium films deposited with increased x or decreased beam voltage and/or substrate temperature, in general, exhibit an increase in their electrical conductivity. The conduction mechanism associated with these films is dominated by hopping between the localized states. The a-Si 50 Ge 50 films deposited at a beam energy of 1000 V and substrate temperature of 300°C have a band gap and an electrical conductivity of 1.1 eV and 3 × 10 −5 (Ωcm) -1 respectively.

Infrared and spectroscopic ellipsometric studies have been done on thin films of hydrogenated amorphous silicon (a-Si:H), germanium (a-Ge:H) and silicongermanium alloy of a typical composition (a-Si28Ge72:H) prepared by reactive ion beam sputtering (RIBS). Films deposited at increasing H2:Ar flow ratio generally show enhanced dihydride and polyhydride bonding and a decreased value of e2max. A correlation of the two results reveals that the increase in hydrogen content affects the growth process considerably and makes the films density deficient and inhomogeneous by increasing the volume fraction of voids, network strains and vacancies. The a-Si28Ge72:H films deposited at increasing H2:Ar flow ratio show a preferential attachment of hydrogen to silicon rather than to germanium. It has been found that RIBS-prepared films are more density deficient as compared to films deposited by glow discharge, owing mainly to the presence of dihydride species.

Electrical and infrared (IR) properties of hydrogenated amorphous germanium (a-Ge:H) films prepared by reactive ion beam sputtering of a high-purity crystalline germanium target under varying deposition conditions have been studied. Minimum conductivity (10-4ω-1cm-1) a-Ge:H films have been obtained for H2:Ar flow ratio of 16:1 at a substrate temperature of 250°C. The films show an activated-type conduction (with an activation energy of 0.36 eV) and a hydrogen concentration of about 11 at.%. The IR spectra reveal absorption bands corresponding to both monohydride (Ge-H) and dihydride (GeH2) groups. The monohydride absorption band is, however, completely absent in films deposited at 350°C for the same H2:Ar flow ratio. X-ray diffraction analysis shows that these films are microcrystalline and show an enhanced electrical conductivity (4.0×10-3ω-1cm-1) with decreased activation energy (0.29 eV).

Screen-printed thick films of the ceramic oxide superconductor material YBa 2 Cu 3 O 7 − x have been prepared on alumina substrates. A buffer layer of glass between the substrate and the oxide film has been used to promote adhesion as well as to decrease the reaction between the substrate and the film and thus to prevent “poisoning” of the superconducting thick film. Structural and electrical properties of the thick films have been studied. The sintered films show an orthorhombic structure with columnar growth with an oriented c axis. The films exhibit onset of superconductivity at 82 K with a 2 K transition width and a critical current density of 100 A cm −1 at 77 K.