Sa. K. Narayandass

Characterization of transparent conducting CdO films deposited by spray pyrolysis

Transparent conducting cadmium oxide (CdO) films have been deposited by spray pyrolysis. The film thicknesses have been determined using Rutherford backscattering spectrometry. X-ray diffraction measurements show that the films are polycrystalline with a preferential orientation along the (111) diffraction plane and the lattice parameter has been calculated. The dislocation density and strain have also been evaluated. The films possess a transmittance of about 75% in the visible and near-infrared region. The refractive index is found to vary between 1.68 and 2.84 in the wavelength range 500-1500 nm. The values of indirect and direct bandgaps obtained are 1.98 and 2.32 eV respectively. Hall effect measurements have been carried out in the temperature range 304-349 K. Resistivity, carrier concentration and mobility of the films at room temperature have been evaluated as 6.6*10-5 Omega m, 1.4*1025 m-3 and 0.68*10-2 m2 V-1 s-1 respectively. Thermoelectric power values from thermoelectric power measurements carried out in the temperature range 304-376 K have been found to be about 19.7-89 mu V K-1. Laser damage studies performed at a wavelength of 1.06 mu m indicate that the films possess a damage threshold density of about 2.37*104 J m-2.

Magnetron sputtered transparent conducting CdO thin films

Thin films of cadmium oxide have been produced by dc reactive magnetron sputtering in nitrogen and oxygen atmosphere. The structural, optical, and electrical characterization of these films are investigated. Structural analysis indicates that the films are polycrystalline and cubic. Composition analysis by Rutherford backscattering spectrometry has been made and it is found that the films contain excess cadmium and deficient oxygen. It is observed from the optical properties that the films possess a transmittance of about 85% in the visible and near infrared regions of the spectrum and direct bandgap values in the range 2.50 to 2.68 eV for films of thicknesses 146 to 177 nm. Electrical measurements point out that the films have resistivity, carrier concentration, and mobility in the range 2.65 to 6.64 × 10-6 Ωm, 1.60 to 2.35 × 1026 m-3, and 57.65 to 100.48 × 10−4 m2 v−1 s−1 respectively.

Growth, structure, dielectric and AC conduction properties of solution grown PVA films

Abstract Polyvinyl alcohol (PVA) films were deposited on pre-cleaned glass substrates using an isothermal immersion technique. Sandwich structures of the type Al-PVA-Al were formed to study the dielectric and conduction properties of PVA films. Aluminium electrodes were deposited by vacuum evaporation method. Thicknesses ( d ) of the dielectric films were measured by an electronic linear thickness measuring instrument (Tesatronic TTD20 model) and a gravimetric method and cross checked by a capacitance method. The dependence of the thickness of the PVA films on the immersion time, concentration and temperature of the solution had been studied. From the X-ray diffraction studies the structure of the deposited film was found to be amorphous. The dielectric properties were studied in the frequency range 1–30 kHz at various temperatures in the range 303–423 K. The capacitance, though dependent on frequency and temperature, was found to be almost invariant at room temperature for all frequencies. The dielectric constant e ′ of the films was found to be increasing with increase in thickness of the film. The loss factor e ″ was found to be increasing with increase in temperature up to the glass transition temperature ( T g ) and decreasing above that ( T g ). From AC conduction studies it was confirmed that the mechanism responsible for conduction is mostly due to ionic hopping. The films showed very high transmittance in the visible to near IR region.

Pulsed laser deposited vanadium oxide thin films for uncooled infrared detectors

Vanadium oxide thin films were deposited by pulsed laser deposition (PLD) technique using V 2O5 as target. A new deposition parameter has been extracted to deposit vanadium oxide thin films at room temperature for uncooled microbolometers. Temperature coefficient of resistance (TCR) is one of the vital bolometric parameters, which influences the performance of the uncooled microbolometer infrared detectors was determined. The TCR values of vanadium oxide films deposited by PLD at room temperature are coinciding with the reported TCR values of successful vanadium oxide thin films deposited at elevated temperatures by other techniques for bolometric applications. We further investigated the influence of laser fluence on the electrical property of the vanadium oxide films.

Structural characterization of cadmium oxide thin films deposited by spray pyrolysis

Abstract A series of CdO thin films have been prepared by spray pyrolytic technique at different substrate temperatures. X-ray diffraction scans confirmed the polycrystalline structure of the films. The films exhibit preferential orientation along the (111) plane. To describe the preferential orientation, the texture coefficient has been calculated and the standard deviation factor has also been evaluated to explain the growth mechanism. Various structural parameters such as lattice parameter, crystallite size, strain, dislocation density and stacking fault probability have been calculated. From the optical measurements, the void concentration has been determined and the results are discussed.

Structural characterization of hot wall deposited cadmium selenide thin films

Cadmium selenide (CdSe) films were prepared by the hot wall deposition technique with different quartz tube lengths under a vacuum of 6.6 mPa onto well cleaned glass substrates to optimize the tube length. The XRD analysis revealed that the films were polycrystalline in nature for smaller tube lengths and for smaller thicknesses, but with increasing thickness and increasing tube lengths a preferred orientation was observed on all substrates. The x-ray diffractograms of the films coated on 0.07 m length tube exhibit preferential orientation along the (103) direction for smaller thicknesses, which changes to the (002) direction as the thickness increases, but the films coated with other tube lengths show preferential orientation along the (002) plane parallel to the substrate at larger thicknesses. The lattice constants and the structural parameters viz., crystallite size (D), dislocation density and strain , were calculated for all the films and it was found that as the tube length increases the grain size and strain decreases up to 0.13 m tube length and increases for 0.15 m tube length. The effects of the substrate were studied by coating the film on steatite, mica and ITO substrates using an optimized tube length (0.15 m). Films coated on glass, mica and ITO have a very smooth surface finish, reflecting like a mirror, and those on steatite have a matt finish. Depending on the adhesiveness and grain size the substrates were chosen for further applications. Studies on the effect of substrate temperature were carried out on the films obtained using 0.15 m quartz tube length. From Rutherford backscattering spectrometry analysis, it was found that as the tube length increases the Cd/Se ratio approaches unity.

Argon and nitrogen implantation effects on the structural and optical properties of vacuum evaporated cadmium sulphide thin films

We have implanted vacuum evaporated cadmium sulphide (CdS) thin films with Ar+ and N+ at different doses. We have analysed the properties of the ion-implanted CdS thin films using x-ray diffraction, optical transmittance spectra and Raman scattering, and we observed the formation of Cd metallic clusters in the ion-implanted films. The bandgap of the Ar+-doped films decreased from 2.385 eV for the undoped film to 2.28 for maximum doping. For the N+-doped film the bandgap decreased from 2.385 to 2.301 eV, whereas the absorption coefficient values increased with the increase of the implantation dose. The effect of indium doping in CdS films is also given for comparison. In these films, we observed that the In atoms were doped interstitially into the CdS rather than substitutionally. Here, also, the bandgap values decreased from 2.39 to 2.30 eV with the increase in In doping concentration. On implantation of both types of ions, the Raman peak position appeared at 299 cm−1, and the full width at half maximum changed with the ion dose. The results are discussed on the basis of ion implantation induced lattice damage, which implies that ion implantation can be applied to tailor-make the properties of this important semiconductor.

Dielectric and electric modulus properties of vacuum evaporated Cd0.8Zn0.2Te thin films

Abstract Cd 0.8 Zn 0.2 Te thin films were prepared by vacuum evaporation technique. The variation of dielectric constant and dielectric loss tangent were found to depend on temperature and frequency. Impedance and electric modulus formalisms were employed in order to gain an insight into the microstructural details of films. A comprehensive study on the relaxation mechanism revealed that the presence of grain and grain boundaries across the film thickness were the basic relaxation phenomenon. The activation energies calculated from the loss tangent and spectroscopic modulus mechanism were found to vary between 1.24 and 0.91 eV for the film of thicknesses 230–800 nm. The frequency analysis of modulus properties showed a distribution of relaxation times. Conductivity plots against frequency at higher frequency suggested the response obeying the universal power law. The role of bulk and grain boundary in the overall conduction process has been discussed with realistic justification. The defect density varies between 2 and 5×10 15 eV −1 m −2 for the films of thicknesses studied.

DC reactive magnetron sputtered CdO thin films

Abstract Cadmium oxide thin films were prepared by DC reactive magnetron sputtering using a Cd target in nitrogen and oxygen atmosphere. The films were characterized using X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), Auger electron spectroscopy (AES), optical transmittivity, Hall effect, and thermoelectric power (TEP). The films are cubic and polycrystalline. RBS measurements indicate that the films are nonstoichiometric with excess cadmium interstitials and deficient oxygen and the results are consistent with the AES studies. Optical measurements on these films show transmittance higher than 85% in the visible and near infrared region of the spectrum and a high direct bandgap value of 2.60 eV. An electrical resistivity as low as 4.33 × 10−6 Ω m is obtained due to the high values of the carrier concentration and mobility.

Correlations between the optical and electrical properties of CdO thin films deposited by spray pyrolysis

Abstract Transparent conducting cadmium oxide (CdO) coatings have been widely used in the fabrication of optoelectronic devices [1]. These deposits have been prepared by various techniques such as sputtering [1, 2], spray pyrolysis [2, 3], activated reactive evaporation [4] and cathodic deposition [5]. This paper is devoted to obtaining a correlation between the optical and electrical properties of undoped cadmium oxide films prepared by the spray pyrolysis technique using cadmium nitrate as the starting material.