The influence of thickness and deposition temperature on the conduction activation energy of CdSe0.2Te0.8 thin films

The electrical conductivity and stability in resistance of CdSe_0.2Te_0.8 thin films in different ambients and deposited at different substrate temperatures were investigated. A reduction in conduction activation energy with increase in film thickness and deposition temperature is accounted for by the fact that in CdSe _x Te_1–x inhomogeneous semiconductor thin films, the potential relief inhomogeneity may be reduced with increase in film thickness and substrate temperature, which results in the decrease of conduction activation energy of the films.     

Electrical transport properties of thallium-doped p-type Pb0.8Sn0.2Te thin films

Hall coefficient and d.c. conductivity studies were made on p-type Pb_0.8Sn_0.2Te thin films doped with different concentrations of thallium in the temperature range 77 to 500 K. The Hall coefficient and Hall mobility are found to decrease with an increase in the doping concentration of thallium. Hall coefficient data have been analysed in the light of a double valence-band model. Various band parameters such as valence band separation, population ratio, mobility ratio and effective mass ratio have been calculated. Hall mobility data have been analysed in the light of lattice- and defect-limited scattering mechanisms.     

Electrical conduction and electron emission of discontinuous thin films

The electrical conductivity of discontinuous thin metal films is assumed to be by a substrate-assisted tunnelling. Electrons travel from one island to another via impurity levels of the substrate surface. Electrons emitted into vacuum obey the Fowler-Nordheim equation for field emission. Field factors are calculated and related to the film structure. It is shown that electrons are emitted from small islands in the cathode region where the main voltage drop occurs.     

Structural investigation of Ge-Sb-Sn thin films using transmission electron microscopy

Atomistic structures of as-deposited and laser-induced-crystallized Ge-Sb-Sn layers have been examined using high-resolution electron microscopy (HREM) and nanobeam electron diffraction (NBED). Cross-sectional observations were performed on Ge-Sb-Sn thin films embedded in a multi-layered structure. Crystalline clusters were frequently observed in the HREM images of the as-deposited amorphous Ge-Sb-Sn thin film. Autocorrelation function analysis of the HREM image indicated a similarity between the structures of the crystalline clusters and that of rhombohedral Sb. Atomic pair-distribution functions obtained from the halo NBED intensity of the as-deposited amorphous Ge-Sb-Sn films also showed development of local structure whose atomic configuration is similar to that of the rhombohedral Sb. NBED revealed that the structure of the crystallized Ge-Sb-Sn thin film is also close to that of rhombohedral Sb. The atomistic structures of Ge-Sb-Sn thin films were compared with those of Ge-Sb-Te thin films and the rapid crystallization mechanism of these materials was discussed.     

Space charge limited conduction in CdSe thin films

The current (I)-voltage (V) characteristics of thermally evaporated CdSe thin films having thickness in the range 850–3000 Å and deposited within the substrate temperature of 303–573 K show nearly linear dependence at low voltage and afterwards a non-linear behaviour at higher voltage range. A detailed study ofI-V curves in dark and under illumination clearly reveals the mechanism as ohmic at low voltage and that of trap limited space charge limited conduction (SCLC) at higher voltage. The transition voltage (V_t) from ohmic to SCLC is found to be quite independent of ambient temperature as well as intensity of illumination. SCLC is explained on the basis of the exponential trap distribution in CdSe films. Trap depths estimated from the lnI vs 10³/T plots are found to be within 0.60-0.37 eV. Using the relevant SCLC theory, the carrier concentration, n₀, total trap concentration, N_t, and the ratio of free charge to trapped charge, θ, have been calculated and correlated with ambient temperature and intensity of illumination.     

Investigation of CdSe x Te1−x : Te composite thin films

Thin films of the composite CdSe _x Te_1–x : Te have been prepared by the thermal coevaporation technique of ingot double-source CdSe powder and Te at 300 K. The films were analyzed by energy dispersion analysis by X-rays (EDAX) and X-ray diffraction techniques and found to have a polycrystalline structure of CdSe _x Te_1–x of hexagonal phase and Te of hexagonal phase for CdSe _x Te_1–x : Te of x ranging from 0.65 to 0.76. There exists SiO₂ of tetragonal phase in as-deposited CdSe : Te films but it is not present in films annealed at a temperature of 413 K. The crystallite size for the composite films was determined and showed the same values for different x values. Optical properties of deposited films were calculated through their optical transmission and reflection spectra. It was observed that the composite films of CdSe _x Te_1–x : Te have two direct transition energies instead of one direct optical transition typical of CdSe films.     

X-ray and transmission electron microscopy structural characterization of multifunctional Perovskite thin films

Different multifunctional (PbTiO₃, Sm_0.6Nd_0.4NiO₃, NdMnO₃) thin films were grown by metalorganic chemical vapor deposition (MOCVD) technique on SrTiO₃ and LaAlO₃ substrates. Transmission electron microscopy (TEM) and X-ray diffraction measurements reveal that almost single crystalline thin films can be epitaxially grown on the top of substrates. The relationship between the crystallographic orientation of the films and those of the substrates were determined by reciprocal space mapping and TEM analyses. PbTi03 thin films appear to be under tensile or compressive strain according to the different mismatch of their cell parameter with those of the substrate. Relaxation mechanism as a function of the film thickness arises from coexistence of different type of domains and size and strain effect are analyzed. SmNiO₃ thin films present diffuse scattering strikes and are less well organized when compared to PbTi0₃ thin films. Different domains are observed as well as an additional parasitic phase close to NiO. Its regular distribution can be associated to reduced transport properties. Preliminary observations on NdMnO₃ thin films shows that an amorphous phase is obtained during MOCVD that can be transformed in a single crystalline film by annealing. The films are under tensile or compressive strain according to the different mismatch of their cell parameter with those of the substrate. Magnetic properties are investigated.     

Electrical conduction of erbium fluoride thin films

Thin-film capacitors of erbium fluoride were fabricated by electron beam gun deposition. The current-voltage characteristics of the erbium fluoride films were studied in the temperature range 323 to 396 K. For sufficiently high electric fields (>10⁴ V cm^–1), the leakage current increases exponentially with the square root of the applied field. Analysis of the data suggests an electrode-limited mechanism such as that suggested by Schottky. It is seen that the conduction mechanism is an activated process with the activation energy decreasing with increasing field.     

Electrical conduction through co-evaporated SiOx-SnO thin films

D.c. electrical properties of SiO _x -SnO (300 nm) thin films forming part of a metal-insulatormetal (MIM) structure are reported. The conduction process is related to the field-assisted thermal excitation of electrons from the trapping centres in the forbidden band gap to the conduction band (Poole-Frenkel effect). The energy gap between the trapping level and the bottom of the conduction band in 80% SiO _x -20% SnO in thin films (300 nm) is found to be equal to 0.50 eV. The level of conduction in the composite films is observed to increase with an increase in the content of SnO.     

Electrical conduction phenomena in thin tetracene films

Thin film aluminium oxide capacitors using anodic Al₂O₃ as the dielectric are described. The dependence of oxide thickness and dielectric loss on anodization voltage was studied. Variation of capacitance with temperature and frequency was also investigated. The capacitors were used in conjunction with tantalum resistors to fabricate an astable multivibrator circuit and the waveforms were recorded. The combination of aluminium oxide capacitors and tantalum resistors has some advantages over all-tantalum RC networks.     

Electrical conduction in Cr-SiO cermet thin films

In one model of electrical conduction in cermet thin films it is assumed that they form a system composed of small metal particles embedded in a solid dielectric. Hill and Coutts (Thin Solid Films, 42 (1977) 201) have found that the value of the power parameter n in the formula describing the temperature dependence of the electrical resistance of such a discontinuous metal film ranges from zero to 0.6. In this study these values for n were verified experimentally for Cr-SiO cermet thin films with various metal concentrations which were deposited by flash evaporation.     

Optical bandgap of Sb0.2Bi1.8Te3 thin films

Sb_0.2Bi_1.8Te₃ Thin Films were grown using the thermal evaporation technique on a (001) face of NaCl crystal as a substrate at room temperature. The optical absorption was measured in the wave number range 500 cm^–1 to 4000 cm^–1. From the optical absorption data the bandgap has been evaluated and studied as a function of the film thickness and deposition temperature. The data indicate absorption through direct interband transition with a bandgap around 0.21 eV. The detailed results are reported.     

Photoconductivity studies of CdSe1−x Te x thin films as a function of doping concentration

Thin films of CdSe_1−x Te _x were prepared by using electro deposition with varying doping concentrations of Te(x). Photoconductive studies as a function of applied field, time, wavelength, and intensity of incident light were carried out at room temperature between 1 and 3·5 eV. After establishing that the electrode contacts made using silver paint were ohmic, it was found that as the concentration of Te(x) increases in CdSe_1−x Te _x , the band gap of the material decreases according to the empirical relationE _g = (2 − 1·5x)eV.     

Electrical conduction in evaporated terbium fluoride thin films

The current-voltage characteristics of thin-film capacitors with evaporated terbium fluoride dielectric have been studied as a function of temperature (in the range 300 to 418 K). For sufficiently high electric fields (> 10⁴ V cm^–1, the leakage current is found to increase exponentially with the square root of the applied electric field. Analysis of the data suggests an electrode-limited mechanism such as that suggested by Schottky. It is seen that the conduction mechanism is an activated process with the activation energy decreasing with increasing field. Dielectric break-down and its dependence on film thickness have also been investigated. Break-down field strength follows the Forlani-Minnaja relation.     

Electrical conduction mechanisms in thin amorphous semiconductor films

An account is given of the different conduction mechanisms possible in thin amorphous semiconductor films. Special attention is paid to the low temperature regime where variable range hopping between states near the Fermi level is supposed to be most important. An attempt is made to assess the significance of fits of the conductivity versus temperature relation to the much-used T^{-$\text{1}\text{4}$} relation proposed by Mott.