Browsing by Author "Zhelev V."

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    Indium-Doped ZnO Thin Films Obtained Using Spray Pyrolysis for Position-Sensitive Photodetection
    (2025-08-01) Bancheva-Koleva P.; Zhelev V.; Petkov P.; Petkova T.
    The main goal of this study was to investigate the properties of ZnO thin films, including pure films and those doped with indium (up to 8 mol%) that was deposited using a spray pyrolysis technique on glass and silicon substrates in order to prepare the position-sensitive structure, Si-SiO2-ZnO:In. To this aim, the present work is focused on investigating the effect of indium concentration on the morphology, structure, and optical properties of the films. X-ray diffraction (XRD) analysis reveals a wurtzite polycrystalline structure. Scanning electron microscopy (SEM) images display a smooth and uniform surface characterized by closely packed nanocrystalline clusters. As the indium concentration rises to 8 mol%, the number of nuclei grows, resulting in uniformly distributed grains across the entire substrate surface. The estimated root mean square (RMS) roughness values for the thin films undoped and doped with 3 mol%, 5 mol%, and 8 mol% of ZnO measured using AFM are 6.13, 9.64, and 13.76 nm, respectively. The increase in indium concentration leads to a slight decrease in film transmittance. The measured LPV photosensitivity of about 44 mV/mm confirms the potential use of these thin films in practical applications.
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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.