Electrical,structural and gas sensing properties of zinc phthalocyanine thin films

The dark conductivity of zinc phthalocyanine (ZnPc) has been studied as a function of material purity, crystal phase transformation and temperature with particular regard to gas sensitivity in air, O₂, N₂, argon, NH₃ and NH₃-air mixtures. α-ZnPc was found to grow in the form of randomly oriented micro- crystallites but the β form showed oriented needle-like and whisker growth. The electrical properties were found to be dependent on material purity. Entrainer- sublimed ZnPc showed higher conductivity than impure material and displayed reproducible linear characteristics with less drift and hysteresis.The conductivity of both α- and β-ZnPc is found to be critically dependent on the presence of O₂. The sensitivity to other gases differs for the α and β forms but in both cases NH₃ causes a large dark conductivity decrease, possibly owing to catalytic behaviour, effectively removing oxygen acceptors.Conductivity-temperature data indicate a transition from extrinsic to non-extrinsic conduction for most cases.The conductivity of β-ZnPc is found to be greater than that of α-ZnPc, in contrast with other phthalocyanines.The relative sensitivities to the various gases suggests that ZnPc may be a viable material for selective gas sensing devices.     

Thermophysical properties of thin metal films

A method is proposed for determining thermophysical properties of thin metallic films, using solutions of converse thermal conductivity problems.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 1, pp. 130–135, January, 1990.     

Transport properties of thin metal films

The electrical conductivity, thermal conductivity and thermoelectric power of a metal film subjected to the simultaneous action of an electric field and a temperature gradient were calculated. Analytical equations for the electrical and thermal current densities in thin metal films were obtained.     

Thermophysical properties of thin metal films

The article discusses methods and results of comprehensive investigations of the thermal conductivity, thermal diffusivity, heat capacity, and structure of films of metals 10–10² nm in thickness.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 4, pp. 606–613, April, 1980.     

Electrical properties of polycrystalline GaInAs thin films

Polycrystalline Ga_xIn_1 − xAs films with x ranging from 0 to 1 were deposited on glass substrates by molecular-beam deposition at 240 or 350 °C. Room temperature Hall-effect measurements showed that the Ga_xIn_1 − xAs films deposited at either temperature exhibit high electron concentrations in the range of 10¹⁸ cm^− 3 for x ≤ 0.21 while the electron concentration decreases with increasing Ga content for x ≥ 0.29 to be < 10¹⁵ cm^− 3 at x = 0.64. Even at the low deposition temperature of 240 °C, the electron mobility remains > 400 cm²/(V s) at x ~ 0.2 and then decreases with Ga content to be ~ 40 cm²/(V s) at x = 0.64. Temperature-varying Hall-effect measurements in the range of 100-390 K revealed that both the electron concentration and mobility of the samples with x ≤ 0.21 are almost independent of the measurement temperature, while those of the samples with x ≥ 0.30 decrease with decreasing measurement temperature. The concentrations and ionization energies of donor levels were deduced from the temperature dependence of the electron concentration with the non-parabolicity of the conduction band taken into account. The temperature dependences of electron mobility in the samples with x ≥ 0.30 are well explained in terms of thermionic electron emission across the grain-boundary barriers assuming fluctuation in potential barrier height, while the almost temperature-independent high electron mobilities in the samples with x ≤ 0.21 are attributed to the absence of potential barrier at the grain boundaries.     

Electrical properties of ZrO2 thin films

Electrical properties of sputtered ZrO₂ thin films have been studied using impedance spectroscopy, isothermal transient ionic current and current–voltage measurements. ZrO₂ have different dielectric properties when fresh, i.e. newly deposited, or aged. A fresh sample can arbitrarily show two different behaviors consisting of a d.c. conductivity with a relaxation peak superimposed on it. The d.c. conductivity shows either of two different values. The aged sample has a lower d.c. conductivity and the relaxation peak is found at much lower frequencies. Fresh samples of ZrO₂ also show switching behavior which aged samples never do. Analyses of current–voltage characteristics indicate hopping as the main conduction process.     

Electrical properties of thin oxidized aluminium films

Thin aluminium films of thickness 40 to 200 nm were deposited on to glass substrates at 573 K in a high vacuum. The deposition was carried out layer by layer and the interfaces between these layers were exposed to oxygen. The electrical resistivity was studied as a function of the film thickness, annealing time, annealing temperature and oxygen pressure. The temperature coefficient of resistivity and the activation energy for the conduction electrons were studied as a function of the film thickness and oxygen pressure. Fuchs-Sondheimer theory for electrical conduction was applied to the experimental results. The mean free path of the conduction electrons was calculated as a function of temperature and agreed well with the theoretical relation.     

Electrical properties of electrodeposited CdTe thin films

The electrical properties of electrodeposited CdTe thin films have been studied. The temperature-dependent electrical conductivity data obtained have been used to determine the conductivity type and semiconductor parameters (E _g, B, and α) of the films.     

Electrical properties of electron-gun-evaporated InAs thin films

Measurements of the resistivity and the Hall coefficient versus the temperature (77–300 K) and the magnetic field (0–11 kG) were performed on InAs thin films (100–1500 Å thick) obtained by vacuum evaporation from an electron gun and condensation onto glass substrates at room temperature. Analysis of the electrical results reveals the typical behaviour of disordered structures. The conductivity versus temperature curves exhibit an anomalous sharp variation which appears to separate two temperature ranges characterized by different conductivity slopes. Observation of the samples in a transmission electron microscope reveals the polycrystalline structure of the films. Electron spectroscopy for chemical analysis shows the sample to be non-stoichiometric with an excess of indium in the inner layers and the presence of indium and arsenic oxides at the surface of the films. Numerical analysis, performed with a multiparametric best-fit procedure, shows that the conductivity conforms to the percolation conductivity model but with an exponential temperature dependence, in accordance in the high temperature region with the more recent hypotheses regarding disordered structures.     

Preparation and properties of zinc phosphide thin films

Zinc phosphide (Zn₃P₂) was prepared by the carbon reduction process. Thin films of Zn₃P₂ were evaporated onto glass substrates at various substrate temperatures. Films evaporated onto substrates at and above 220 °C were polycrystalline in nature. Films of different thicknesses were grown and their electrical conductivity was measured in the temperature range 100–300 K. Four characteristic energy gaps of 1.3, 1.66, 1.75 and 1.82 eV were obtained from the analysis of the optical absorption spectrum.     

Electrical properties of electron-beam-evaporated indium oxide thin films

Crystalline (b.c.c.) indium oxide (In₂O₃) powder was evaporated using an electron beam and the structure of the deposited films was found to be amorphous. Studies of the a.c. conductance of films of various thicknesses were carried out in the audio frequency range (200 Hz to 30 kHz) at various temperatures. The current-voltage characteristics of the films were also studied. The dielectric breakdown field strength was determined for several film thicknesses and at various temperatures. The activation energies for the a.c. and d.c. conduction processes were estimated and the results are discussed.     

Electrical properties of vanadium tungsten oxide thin films

The vanadium tungsten oxide thin films deposited on Pt/Ti/SiO₂/Si substrates by RF sputtering exhibited good TCR and dielectric properties. The dependence of crystallization and electrical properties are related to the grain size of V_1.85W_0.15O₅ thin films with different annealing temperatures. It was found that the dielectric properties and TCR properties of V_1.85W_0.15O₅ thin films were strongly dependent upon the annealing temperature. The dielectric constants of the V_1.85W_0.15O₅ thin films annealed at 400 °C were 44, with a dielectric loss of 0.83%. The TCR values of the V_1.85W_0.15O₅ thin films annealed at 400 °C were about −3.45%/K.     

Electrical and optical properties of TiN thin films

TiN thin films have been grown by reactive magnetron sputtering. It has been shown that an Ohmic contact to TiN thin-film can be made from indium. The TiN thin films have been shown to be n-type semiconductors with a carrier concentration of 2.88 × 10²² cm^?3 and resistivity of ρ = 0.4 Ω cm at room temperature. The activation energy for conduction in the TiN films at temperatures in the range 295 K < T < 420 K is 0.15 eV. The optical properties of the TiN thin films have been investigated. The material of the TiN thin films has been shown to be a direct gap semiconductor with a band gap E _g = 3.4 eV.     

Electrical properties of thermally evaporated tellurium thin films

Results of dielectric and conduction properties of vacuum evaporated tellurium (Te) thin film capacitors (Al-Te-Al) have been reported in the frequency range 1–100 kHz at various temperatures (303–423 K). Loss factor (tanδ) which shows a maximum with frequency increases with rise of temperature and tanδ _max shift towards high frequency region. The large values of capacitance and dielectric constant (ɛ′) in the low frequency region indicate the possibility of an interfacial polarization mechanism.I-V characteristics show ohmic, space charge limited (SCLC) and thermionic emission conduction mechanisms to operate at low, intermediate and high voltages respectively. Various transport parameters have been calculated. It has been observed that the Schottky type of conduction is predominant in the high field region and the Schottky barrier height has been determined. The Hall coefficient, Hall mobility and carrier concentration are also discussed.     

Electrical properties of thin V-A1 alloy films

The electrical properties of V-Al alloy films of various thicknesses and compositions were studied. The V-Al films were evaporated using an electron gun in vacuum (pressure p ≈ 10^-5 Pa) onto quartz substrates at room temperature. The film resistivity vs. temperature was measured in situ in a vacuum of 10^-8-10^-6 Pa at temperatures ranging from 300 to 850 K. A saturation effect was observed in the resistivity. The above findings were analysed in terms of the shunt resistance model.