Electrical conduction and transmission electron microscopy studies of CdSe0.8Te0.2 thin films

Electrical resistance of CdSe_0.8Te_0.2 thin films were found to be dependent on various film parameters such as substrate temperature, film thickness, deposition rate and post-deposition heat treatment in different environments. A decrease in film resistivity was observed for thicker films and for those heat treated in vacuum. Films deposited at higher substrate temperatures and faster rates showed an increase in film resistivity. A spectrum of activation energies was observed in the films which fell within either of the activation energies observed in CdSe or CdTe films. Films heated in an oxygen environment showed an increase in film resistivity with a different activation energy. Transmission electron microscopy (TEM) of the films showed an improvement in crystallinity with increasing film thickness and substrate temperature, and a reduction in crystallinity with increasing deposition rate.     

Fabrication and characterization of n-CdSe0.7Te0.3/p-CdSe0.15Te0.85 solar cell

Hot wall deposited CdSe_xTe_1−x where 0 ≤ x ≤ 1 thin films for solar cell applications have been prepared from a compound synthesized by direct reaction of high purity Cd, Se and Te elements. Crystal structure and composition of the films were analyzed by X-ray diffraction, scanning electron microscope and EDAX. X-ray diffraction studies carried out on pseudo-binary system revealed that the films are polycrystalline in nature with CdSe_0.7Te_0.3 film exhibiting hexagonal structure and CdSe_0.15Te_0.85 film exhibiting cubic zinc blende structure. The type of conduction was determined by Hall studies. A novel solar cell with structure n-CdSe_0.7Te_0.3/p-CdSe_0.15Te_0.85 has been fabricated and the efficiency was found to be 3.13%.     

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.     

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.     

Photosensitivity and spectra of deep local states in sintered films of cadmium selenide and cadmium telluride alloys

The photoconductive and luminescence properties of non-intentionally doped and copper-doped CdSe_xTe_1−x (x=0−1) films were studied. The films were prepared by spraying an aqueous suspension of mixtures with varying composition onto ceramic substrate. Both the energy gaps determined using photoconductivity spectra and the maxima of the luminescence bands as functions of the film composition x were obtained. The correlation of the luminescence intensity and the photoconductivity with x was established. Using the decay curves of photocurrent excited under “light impact” conditions the electron capture cross-sections of the recombination centres in the films under investigation were estimated. The nature of the recombination centres in CdSe_xTe_1−x (x=0–1) films both copper free and copper doped are discussed.     

Electrical and optical properties of Indium sesquitelluride (In2Te3) thin films

Indium sesquitelluride (In₂Te₃) thin films were grown on glass substrates using a flash evaporation technique. The nature of contact phenomena of Ag, Sn, In, Zn, Al-(p) In₂Te₃ junctions had been investigated. Ag, Sn, In and Zn metals were found to provide ohmic contact for In₂Te₃ thin films. The variation of DC-electrical resistivity of In₂Te₃ thin films with temperature was studied at different substrate temperatures. The optical measurements revealed that the flash evaporated In₂Te₃ thin films possessing direct energy band-gap. The variation of optical energy gap with substrate temperature was investigated. Film thickness, substrate temperature, composition and crystallinity were found to determine the optimization of electrical and optical properties of In₂Te₃ thin film.     

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.     

Thickness and temperature effects on electrical resistivity of (Bi0.5Sb0.5)2Te3 thin films

Thin films of (Bi_0.5Sb_0.5)₂Te₃ of different thickness were deposited on glass substrate by the flash evaporation method in a vacuum of 1 × 10^− 5 Torr. X-ray diffraction and transmission electron microscope analysis indicates that these films are polycrystalline even in the as-deposited state and the post-deposition annealing leads to grain growth. Electrical resistivity studies were carried out on these films as a function of temperature (300– 450 K) and film thickness (450–2000 Å). Temperature dependence of electrical resistivity shows that (Bi_0.5Sb_0.5)₂Te₃ films are semiconducting. It is found that electrical conduction activation energy decreases with increase of film thickness and this observation is explained based on the Slater model. Thickness dependence of electrical resistivity is analyzed using the effective mean free path model of size effect with perfect diffuse scattering. This analysis leads to the evaluation of the important physical parameters i.e., mean free path and bulk resistivity of hypothetical bulk.     

Some optical properties of Se-Ge-As amorphous chalcogenide glasses

The effects of composition, film thickness, substrate temperature, and annealing of amorphous thin films of Se₇₅Ge_25−x As _x (5⩽x⩽20) on their optical properties have been investigated. X-ray diffraction revealed the formation of amorphous films. The absorbance and transmission of vacuum-evaporated thin films were used to determine the band gap and refractive index. Optical absorption measurements showed that the fundamental absorption edge is a function of glass composition and the optical absorption is due to indirect transition. The energy gap increases linearly with increasing arsenic content. The optical band gap,E _opt, was found to be almost thickness independent. The shapes of the absorption edge of annealed samples displayed roughly the same characteristic as those of the unannealed films, but were shifted towards shorter wavelengths; as a result,E _opt increased andE _e, the width of the band tails, decreases. The increase inE _opt is believed to be associated with void removal and microstructural re-arrangement during annealing. The influence of substrate temperature on the optical parameters is discussed.     

Electrical and crystallographic properties of nanocrystalline CdSe<Subscript>0.5</Subscript>S<Subscript>0.5</Subscript> composite thin films deposited by dip method

A dip method is employed for the deposition of CdSe_0.5S_0.5 composite thin film at room temperature. Cadmium sulphate, thiourea and sodium selenosulphate were used as the basic source material. Solid solution with cubic phase was observed from X-ray diffraction studies. The specific conductivity of the film was found to be in order of 10⁻⁷ (Ωcm)⁻¹. The temperature dependence of an electrical conductivity, thermoelectrical power, carrier density and carrier mobility for CdSe_0.5S_0.5 thin films have been examined. The low temperature conductivity is governed by a variable range of conduction while grain boundary limited conduction mechanism is predominant at higher temperature.     

Effect of In additive on the photosensitivity of glassy Se80Te20 alloy

Photo-electrical measurements are done on thin films of Se_80?x Te₂₀In _x (0 ≤ x ≤ 20) to see the effect of In on the photoconductive properties of binary Se₈₀Te₂₀ alloy. The photosensitivity (σ_ph/σ_d) and activation energy of photoconduction (ΔE _ph) are determined for this purpose. It has been found that σ_ph/σ_d and ΔE _ph are decreased with increasing concentration of the third element. The results are explained in terms of the increase in density of the defect states with the increase in concentration of the additive in thin films of Se_80?x Te₂₀In _x .     

Study of non-isothermal kinetics, electrical and optical properties of (GaSeTe) films

Ternary Ga_xSe_86−xTe₁₄ amorphous films (x=15 and 36) were prepared by thermal evaporation. The results of differential scanning calorimetry (DSC) at different heating rates are reported and discussed. The glass transition activation energy, E_t, and the crystallization activation energy, E_c, were evaluated by measuring the heating rate dependence of the glass transition, crystallization onset and peak crystallization temperatures. The average calculated values of E_t and E_c are 140.29 and 97.89 kJ/mol, respectively. The electrical conductivity of amorphous Ga_xSe_86−xTe₁₄ thin films with different thickness has been measured in the temperature range (263.2-333.3 K) and this allows the effect of introducing a metallic impurity to be observed. It was observed that conductivity increases with increasing activation energy and with a lowering of the pre-exponential factor, which suggests the results can be explained in terms of hopping conduction. The optical constants of these films were determined by transmission and reflection measurements at normal incidence in the spectral range of 500-800 nm. The refractive index has anomalous behavior in the spectral range 400-500 nm. The refractive index dispersion can be fitted to a single oscillator model.     

Structural, optical and photoelectrochemical properties of brush plated CdSe x Te1 − x thin films

CdSe _x Te_{1 – x} films have been deposited by the brush plating technique for the first time, on titanium and conducting glass substrates at room temperature. These films were annealed in argon atmosphere at 475°C for 15 min. Their structural, optical and photoelectrochemical (PEC) properties are presented and discussed. The power conversion efficiency has been found to be 9.0% at 60 mW cm^–2white light illumination. A peak quantum efficiency of 0.7 has been obtained for the films of composition CdSe_0.7Te_0.3. Donor concentration of 10¹⁷cm^–3and electron mobility of 60 cm²V^–1sec^–1were obtained.     

Structural and electrical studies of Cd<Subscript>1−x</Subscript>Zn<Subscript>x</Subscript> Te thin film by vacuum evaporation technique

Cd_1−xZn_xTe (where x = 0.02, 0.04, 0.06, 0.08) thin film have been deposited on glass substrate at room temperature by thermal evaporation technique in a vacuum at 2 × 10⁻⁵ torr. The structural analysis of the films has been investigated using X-ray diffraction technique. The scanning electron microscopy has been employed to know the morphology behaviour of the thin films. The temperature dependence of DC electrical conductivity has been studied. In low temperature range the thermal activation energy corresponding to the grain boundary—limited conduction are found to be in the range of 38–48 μeV, but in the high temperature range the activation energy varies between 86 and 1.01 meV. The built in voltage, the width of the depletion region and the operating conduction mechanism have been determined from dark current voltage (I–V) and capacitor-voltage (C–V) characteristics of Cd_1−xZn_xTe thin films.     

Preparation and investigation on glasses in the Te46As32Ge10Si12 and Te41As37Ge10Si12 systems

Thin films of Te_46–xAs_32+xGe₁₀Si₁₂ (x=0,5) of different thicknesses are deposited on glass substrate by vacuum evaporation. X-ray diffraction revealed the formation of amorphous films. The value of the optical band gap, E _g, is found to increase with the thickness of the films and with increasing As content. The films are heat treated at different elevated temperatures from 298 to 423 K. The values of E _g are found to decrease with increasing temperature of heat treatment. The band tail, E _e, obey Urbach's empirical relation.     

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.     

High speed and low power consumption of superlattice-like Ge/Sb<Subscript>70</Subscript>Se<Subscript>30</Subscript> thin films for phase change memory application

In comparison to Ge₂Sb₂Te₅ (GST) and pure Sb₇₀Se₃₀ (SbSe) thin films, superlattice-like (SLL) Ge/Sb₇₀Se₃₀ (Ge/SbSe) has a higher crystallization temperature, larger crystallization activation energy, better data retention and lower power consumption. SLL Ge/SbSe thin films with different thickness of Ge and SbSe layers were prepared by magnetron sputtering system. The amorphous-to-crystalline transitions of SLL Ge/SbSe thin films were investigated through in situ film resistance measurement. The crystallization activation energy of SLL Ge/SbSe thin films was calculated from a Kissinger plot. The data retention time was estimated through isothermal time-dependent resistance measurement by Arrhenius equation. The phase structure of the thin films annealed at different temperatures was investigated by using X-ray diffraction. Phase change memory cells based on the SLL [Ge(8 nm)/SbSe(5 nm)]₄ thin films were fabricated to test and evaluate the switching speed and operation consumption.     

A study of photosensitive sintered films of CdSexTe1−x solid solutions

Photosensitive polycrystalline sintered films of CdSe_xTe_1−x solid solutions were prepared and their phase compositions, homogeneity and photoelectric and relaxation properties were studied. It was found that polycrystalline CdSe_xTe_1−x films show better response rates than other wide gap A^IIB^VI compounds, and their photosensitivity peaks are shifted into the near-IR region and can be varied between 0.72 and 0.92 μm.     

Heat sensitive property of sputtered titanium oxide thin films for uncooled IR detector application

Titanium oxide (TiO_x) thin films were deposited on thermally grown Si₃N₄-film-coated Si substrates by dc reactive magnetron sputtering. The crystallographic structure, microscopic morphology, electrical resistivity, temperature coefficient of resistance (TCR) and activation energy of the films were proven as functions of the oxygen partial pressure (pO₂) and substrate temperature (T _s ). The mixed valence TiO_x thin films deposited with temperature from 30 to 250 °C in different pO₂ present various electrical properties even though all the samples are amorphous. The TCR and activation energy of the films vary with different pO₂ and T _s . It has been demonstrated that the sputtered TiO_x films are promising heat sensitive materials for uncooled Infrared detector application.     

Electronic conduction in bulk Se1−x Te x glasses at high pressures and at low temperatures

The electrical resistivity of bulk Se_1−x Te _x glasses is reported as a function of pressure (up to 8 GPa) and temperature (down to 77K). The activation energy for electronic conduction has been calculated at different pressures. The samples with 0⩽x⩽0·06 show a single activation energy throughout the temperature range of investigations. On the other hand samples with 0·08⩽x⩽0·3 show two activation energies in the different regions of temperature. The observed behaviour has been explained on the basis of band picture of amorphous semiconductors.