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Access type: UnknownSubject: search.filters.subject.Thermal evaporation

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    Structural, optical and photoconductive properties of thermally evaporated CdSxTe1-x thin films
    (2017-10-01)
    Gaewdang, Thitinai
    ;
    Wongcharoen, Ngamnit
    The formation of a CdS<inf>x</inf>Te<inf>1-x</inf> layer by the interdiffusion of S into the CdTe and of Te into CdS films occurs during the fabrication of CdS/CdTe thin film solar cells. The CdS<inf>x</inf>Te<inf>1-x</inf> layer is thought to be important because the real electrical junction is located in this interdiffused CdS<inf>x</inf>Te<inf>1-x</inf> region. Thus, it is important to have a full understanding of the physical properties of CdS<inf>x</inf>Te<inf>1-x</inf> alloy thin films. In this study, CdS<inf>x</inf>Te<inf>1-x</inf> thin films with composition 0 ≤ x ≤ 1 were prepared by thermal evaporation method on glass substrate using powder of pure CdS and CdTe compounds pressed in pellet form as the source in a vacuum of 5.5 10<sup>-5</sup> mbar. X-ray diffraction (XRD) revealed that the films exhibited a cubic zincblende structure with the preferred orientation of (111) plane when x < 0.2. However, when x ≥ 0.8, they had a hexagonal wurtzite structure with the preferred orientation of (002) plane. For the composition 0.2 ≤ x ≤ 0.6, the cubic and hexagonal phases coexisted in the system and the films became less preferentially oriented. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the morphological features of the samples. The transmission spectra of the films were studied using a double beam spectrophotometer in the wavelength range of 300-900 nm. Optical band gap value of the films was determined from the transmittance spectra. The variation of band gap (E<inf>g</inf>) with composition (x) of the films was in good agreement with the quadratic form, giving a bowing parameter of (b) =1.85 eV. From the transient photoconductivity measurements, persistent photoconductivity (PPC) behavior was observed. The decay current data fit better with multiple exponential functions, resulting in five slow decay times. The longest carrier lifetime of approximately 6,000 s was observed in the films with x = 0.8. Density of trap states corresponding to decay time was also evaluated from the decay current data.
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    Influence of annealing temperature on the properties of SnS thin films prepared by vacuum thermal evaporation
    (2017-01-01)
    Wongcharoen, Ngamnit
    ;
    Gaewdang, Thitinai
    SnS thin films were deposited by thermal evaporation in vacuum on glass slide substrate. The as-deposited films were thermally annealed in a controlled N<inf>2</inf> atmosphere with annealing temperature in the range 100-500°C for 30 min. XRD, AFM, UV-VIS transmittance, FTIR and Hall effect measurements were used for characterization the as-deposited and annealed films. Based on the XRD patterns, the as-deposited and annealed films were indentified as the orthrombic structure. The band gap was found to increase from 1.15 to 1.42 eV when the annealing temperature increased from 100 to 500°C. The lowest resistivity and highest carrier concentration values were observed to be 12.95 Ω. cm and 1.98×10<sup>16</sup>cm<sup>-3</sup>on the films annealed at 100 and 200°C, respectively.
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    Effect of annealing temperature on the optical parameters of CdS thin films prepared by thermal evaporation method
    (2013-10-04)
    Gaewdang, Thitinai
    ;
    Wongcharoen, Ngamnit
    ;
    Wongcharoen, Tiparatana
    CdS thin films were prepared by thermal evaporation onto glass substrate in vacuum better than 5.5x10<sup>-5</sup> mbar. The obtained films were subsequently annealed in a pure nitrogen atmosphere at temperature between 100 to 500°C for 30 min. The crystal structure and surface morphology of the as-deposited and annealed films were investigated by XRD and SEM, respectively. Optical band gap and Urbach tail values of the films, determined from spectral transmission data, were found to be slightly varied in the range 2.36-2.40 eV and 110-160 meV, respectively, due to annealing temperature. The refractive index of the films was also evaluated from the spectral transmission data. The dependence of the refractive index on the wavelength obeys the single oscillator model, from which the important parameters such as refractive index, extinction coefficient, oscillator energy (E<inf>0</inf>) and dispersion energy (E<inf>d</inf>) of the films with different annealing temperatures were determined. From the experimental results, the optical parameters of the films are obviously influenced by annealing temperature. © (2013)Trans Tech Publications,Switzerland.