The electrical properties of polycrystalline ZnIn2Te4 thin films

Thin films of ZnIn₂Te₄ are grown onto glass substrates by the flash evaporation technique. Electrical properties such as electrical resistivity and activation energy were studied with different substrate temperatures ranging from 300 to 623 K. It is observed that the film grown at a substrate temperature of 523 K is a single phase polycrystalline stoichiometric film with minimum electrical resistivity. The effect of the film thickness on the electrical properties of ZnIn₂Te₄ thin films grown at a substrate temperature of 523 K has been studied. The experimental data can be satisfactorily explained on the basis of the Fuchs-Sondheimer theory.     

Growth and optical properties of ZnIn2Se4 films

Thin films of ZnIn₂Se₄ were deposited on quartz substrates at 297 K by the conventional thermal evaporation technique. The as-deposited films were amorphous. On annealing at 623 K under vacuum for 3 h, the films crystallized with a preferred (1 1 2) orientation corresponding to the chalcopyrite-type structure. Films deposited on a quartz substrate heated to 573 K were also crystalline. The optical constants were computed from the measured transmittance and reflectance at normal incidence of light in the wavelength range 400 to 2000 nm. The analysis of the data gave a direct gap of 2.2 and 2.06 eV for the amorphous and crystallized films, respectively. The dispersion curve exhibited a peak above the absorption edge. An indirect gap of 1.8 eV for the crystallized films and a direct forbidden gap of 1.75 eV for the amorphous films were also deduced. A direct allowed transition with a gap of 2.065 eV and an indirect transition with a gap of 1.69 eV were deduced for the crystalline films deposited on the heated substrate.     

Memory switching of ZnGa2Te4 thin films

Electrical and switching property of amorphous defect chalcopyrite ZnGa₂Te₄ thin films prepared by thermal evaporation technique has been studied. The elemental chemical compositions of the prepared bulk as well as the as-deposited film were determined by means of energy dispersive X-ray spectrometry. X-ray diffraction pattern revealed that the powder compound is polycrystalline and the as-deposited and the annealed films at t _a ≤ 548 K have the amorphous phase, while that the annealed at t ≥ 573 K are polycrystalline with a single phase of a defect chalcopyrite structure similar to that of the synthesized material. The great advantage of this material is the capability to appear in two different phases, the amorphous and the crystalline phases, with rather different electrical properties. Both dynamic and static I–V characteristics and the switching phenomenon at 601 nm are investigated. The threshold switching mechanism was explained by a thermal model of switching, i.e., joule heating with an electrically conducting channel. ZnGa₂Te₄ is good candidate in phase change memory device.     

Growth and electrical transport properties of In2Te3 thin films

Hall coefficient and d.c. conductivity studies in the temperature range 100–625 K were made on polycrystalline In₂Te₃ films grown on glass and mica substrates. When the films were cycled above about 525 K the conductivity was found to be irreversible; this is explained in terms of structural changes at high temperature. It was found that the Hall mobilities of the films are independent of temperature, showing the predominance of neutral impurity scattering over again boundary scattering.     

Optical properties of Bi2Te2Se thin films

Some optical parameters of Bi₂Te₂Se thin films, determined from the measured absorbance and transmittance at normal incidence in the visible spectral range, were studied as functions of film thickness and annealing temperature. These parameters were found to be sensitive to both film thickness and microstructure change caused by annealing in a film. The effect of thickness and temperature of annealing on the optical gap was interpreted in terms of elimination of defects and change of disordering in the amorphous matrix.     

Growth and characterization of CuInSe2 thin films

Films of CulnSe₂ have been grown using a technique similar to close-spaced vapour transport. The effect of substrate temperature and the distance of the substrate from the source have been optimised to grow well-oriented chalcopyrite phase of CuInSe₂. D.c. conductivity and Hall coefficient studies have been made in the temperature range 77–300 K. The films grown at a substrate temperature of 350 °C have an electron mobility of 3.4×10³ cm²V^–1 s^–1 at 77 K.     

Growth and properties of CuInS2 thin films

Single phase copper indium disulphide (CuInS₂) thin films of thickness between 60 nm and 650 nm with the chalcopyrite structure are obtained on NaCl and glass substrates by flash evaporation. The films were found to ben-type semiconducting. The influence of the substrate temperature on the crystallinity, conductivity, activation energy and optical band gap was studied. An improvement in the film properties could be achieved up to a substrate temperature of 523 K at a molybdenum source temperature of 1873 K.     

Thermoelectric properties of Sb2Te3 thin films by electron beam evaporation

This study applies the thermoelectric grains of Sb2Te3 on conductive glass to evaporate Sb2Te3 thin films by the electron beam evaporation method. Through experimental tests with different evaporation process parameters and film annealing conditions, thin films with better Seebeck coefficient, resistivity (p) and power fact (PF) can be obtained. Experimental results show that when thin films are annealed, their defects can be decreased accordingly, and carrier mobility can be enhanced to further elevate the conductivity of thin films. When the substrate temperature is set at 200 degrees C to fabricate Sb2Te3 thin films by the evaporation process and by annealing at 220 degrees C for 60 minutes, the Seebeck coefficient of Sb2Te3 thin films increase from 87.6 microV/K to 177.7 microV/K; resistivity falls from 6.21 m ohms-cm to 2.53 m ohms-cm and PF can achieve the maximum value of 1.24 10(-3) W/K2 m. Finally, this study attempts to add indium (In) to Sb2Te3 thin films. Indium has been successfully fabricated In3SbTe, thin films. This study also analyzes the effects of In on the thermoelectric properties of In3SbTe2 thin films.     

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.     

FP-LAPW investigation of structural,electronic, linear and nonlinear optical properties of ZnIn2Te4 defect-chalcopyrite

A theoretical study of structural, electronic, linear and nonlinear optical properties of ZnIn₂Te₄ defect-chalcopyrite is presented using the full-potential linearized augmented plane-wave (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA). Moreover, the Engel and Vosko GGA formalism (EV-GGA) is also used to improve the band gap results. The lattice parameters (a, c) and the atomic positions (x, y and z) are optimized and found in good agreements with the available experimental data. Our calculations performed for band structure and density of state show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Γ resulting in a direct energy gap of about 0.89 eV for GGA and 1.20 eV for EV-GGA. The linear optical properties namely, the real and imaginary parts of the dielectric function and the reflectivity spectrum are calculated. This compound possesses a considerable negative birefringence. Based on the density functional theory the nonlinear optical properties are calculated and their spectra are analyzed.     

Growth of AgGaSe2 thin films

Bulk AgGaSe₂ was prepared by melting the pure constituents in stoichiometric proportions. Thin films of this material were grown by a flash evaporation technique. The bulk material and the films were characterised by X-ray and electron microscope techniques. The effects of substrate temperature on the structural properties, compositional analysis and electrical resistivity of films have been studied. It was found that polycrystalline stoichiometric films of AgGaSe₂ can be grown in the substrate temperature range of 423–523 K and the films deposited at 523 K have a minimum electrical resistivity. The implications are discussed.     

Growth of AgInSe2 thin films

Bulk AgInSe₂ was prepared by melting the constituent elements in stoichiometric pro proportions. Thin films were then grown from the bulk by a flash evaporation technique. X-ray diffraction studies were carried out on both the bulk material and the thin films. The data obtained were compared with data reported in the literature. The effect of the substrate temperature on the orientation of the films was also studied by electron diffraction. It was found that polycrystalline films of AgInSe₂ can be grown in the temperature range 150–250 °C.     

Growth of selenium thin films

Quantitative measurements of the formation and growth of selenium films on sapphire, glass, aluminium and nickel substrates have been made for various substrate temperatures (T) and evaporation times (t) using a scanning electron microscope (SEM). The film formation and growth process was thought to be a mechanism of the adsorption of impinging selenium atoms on the stable clusters, and the growth of these clusters as evaporation continues. The difference in the values of the activation energies for the growth of selenium on different substrates was explained by considering them as apparent energies which contain the adsorption, desorption, surface diffusion and binding energy terms. The experimental results also indicated an increase in there-evaporation of adatoms from the substrates at higher temperatures.     

Nanostructure and thermal power of highly-textured and single-crystal-like Bi2Te3 thin films

Bi2Te3-based alloys are known to have outstanding thermoelectric properties.Although structure-property relations have been studied,still,detailed analysis of t...     

Thermoelectric properties of the flash-evaporated n-type Bi2Te2.4Se0.6 thin films

The electronic transport properties of the flash-evaporated n-type Bi₂Te_2.4Se_0.6 thin films have been investigated. The thickness dependence of Seebeck coefficient and electrical resistivity has been analyzed by the effective mean free path model. It was found that both the Seebeck coefficient and the electrical resistivity have a linear relation with the reciprocal of film thickness. The data analyzed by the effective mean free path model have been combined to evaluate important material parameters such as mean free path, its energy dependence, and Fermi energy. Annealing effects on the electronic transport properties have been also examined in conjunction with the antistructure defects. It was found that the annealing treatment is necessary for Bi₂Te_2.4Se_0.6 thin films to reduce the antistructure defects and to improve their thermoelectric properties.