• Sunny Mathew

      Articles written in Bulletin of Materials Science

    • Photoconductive and ellipsometric studies of spray pyrolysed CdS thin films

      A G Valyomana Sunny Mathew K P Vijayakumar C Purushothaman

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      The influence of annealing temperature on photoconductivity of spray pyrolysed CdS films has been investigated. The annealing of films at 373K resulted in maximum photoconductivity. The photoconductivity at all wavelengths was found to decrease with increase of annealing temperature and became a minimum at 473K. For films annealed at or above 523K, the photoconductivity for wavelengths ⩾560 nm decreased considerably. The results are discussed with the help of ellipsometric data, visible and IR spectra of these samples. Also the variation in photoconductivity of these samples were studied during heating to analyse the effect of trapping.

    • Optical constants of CdS thin films prepared by spray pyrolysis

      Sunny Mathew K P Vijayakumar

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      CdS thin films were prepared by spray pyrolysis techniques. Variable angle spectroscopic ellipsometry was used for optical constant calculations. Multiple angle measurements were taken in the most sensitive angle of incidence region. The sensitive regions of angle of incidence were obtained theoretically using 3-dimensional graph ofδψ andδΔ. Real partn and imaginary partk of the complex refractive index of the samples were calculated in the wavelength range 470–650 nm, taking into account surface roughness. Bruggeman’s effective medium approximation is used for analysis of the surface rough layer of the thin films.

    • Ellipsometric studies of microscopic surface roughness of CdS thin films

      Sunny Mathew K P Vijayakumar

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      Analysis of changes in surface roughness of CdS thin films with preparation temperature was carried out using variable angle spectroscopic ellipsometry (VASE). The films studied were prepared by spray pyrolysis technique, in the substrate temperature range 200–360°C. The VASE measurements were carried out in the visible region below the band gap (Eg=2·4eV) of CdS so as to reduce absorption by the film. The thickness of the films was in the range 500–600 nm. Bruggeman’s effective medium theory was used for analysis of the surface roughness of the film. The roughness of the film had a high value (∼ 65 nm) for films prepared at low temperature (200°C) and decreased with increase in substrate temperature. This reached minimum value (∼ 27 nm) in the temperature range 280–300°C. Thereafter roughness increased slowly with temperature. The growth rate of the films was calculated for different temperature ranges. It was found that the deposition rate decreases with the increase in substrate temperature and have an optimum value at 300°C. Above this temperature deposition rate decreased sharply. The scanning electron micrograph (SEM) of the film also showed that the film prepared at 280–300°C had very smooth surface texture.

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