Browsing by Author "Bancheva-Koleva P."

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    EXPLORING THE STRUCTURAL AND ELECTRONIC CHARACTERISTICS OF AMORPHOUS Ge – Te - In MATERIAL THROUGH AB INITIO METHODS
    (2024-01-01) Zaidan A.; Ivanova V.; Petkov P.; Bancheva-Koleva P.
    This study employs density functional theory (DFT) and molecular dynamics to meticulously investigate the structural and electronic properties of ternary chalcogenide compounds, specifically (GeTe4)1-x Inx, and (GeTe5)1-x Inx across a range of compositions ( x = 0, 5, 10, 15, 20 at %). Utilizing the local density approximation within the framework of first-principles calculations, we comprehensively analyze the pair correlation function, static structural factor, electronic density of states, and electronic band gap energy. Our results reveal a notable decrease in the energy band gap of Germanium-Tellurium with the incorporation of Indium atoms. The structural changes observed in the Ge-Te matrix with Indium doping, as evidenced by the changes in the pair correlation function and static structure factor, are consistent with and supportive of the observed decrease in the band gap energy. This phenomenon is primarily attributed to the significant contribution of Indium atoms to the conduction band edge, offering new insights into the material’s electronic behaviour.
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    Molybdenum-Doped ZnO Thin Films Obtained by Spray Pyrolysis
    (2024-05-01) Bancheva-Koleva P.; Zhelev V.; Petkov P.; Petkova T.
    A batch of ZnO thin films, pure and doped with molybdenum (up to 2 mol %), were prepared using the spray pyrolysis technique on glass and silicon substrates. The effect of molybdenum concentration on the morphology, structure and optical properties of the films was investigated. X-ray diffraction (XRD) results show a wurtzite polycrystalline crystal structure. The average crystallite size increases from 30 to 80 nm with increasing molybdenum content. Scanning electron microscopy (SEM) images demonstrate a smooth and homogeneous surface with densely spaced nanocrystalline grains. The number of nuclei increases, growing over the entire surface of the substrate with uniform grains, when the molybdenum concentration is increased to 2 mol %. The estimated root mean square (RMS) roughness values for the undoped and doped with 1 mol % and 2 mol % of ZnO thin films, defined by atomic force microscopy (AFM), are 6.12, 23.54 and 23.83 nm, respectively. The increase in Mo concentration contributes to the increase in film transmittance.