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Al-IB family -doped ZnO thin films and first-principles calculations

Author: FangLaiPeng
Tutor: TanHongLin
School: Kunming University of Science and Technology
Course: Materials Science
Keywords: ZnO thin films sol-gel first principles and pseudopotentials method dopant
CLC: TB383.2
Type: Master's thesis
Year: 2010
Downloads: 69
Quote: 0
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Abstract


Zinc oxide is one kind of direct band gap semiconductor materials (Eg=3.37eV at RT)with a high exciton binding energy of about 60 meV. It has high transmittance for the visible light and high absorption for ultraviolet. Therefore, it was considered to be a new photo-electric material in shortwave length as GaN. It Can be used to fabricate display,window materials for solar cells, surface acoustic wave devices, luminescence diode and voltage varistors. Recently, ZnO thin film attracts much attention in semiconductor materials research field.In this paper, the various growth techniques of ZnO films and the progresses in the internal and overseas researchs of ZnO were reviewed.In this paper, the ZnO thin films were prepared on glass substrate (microscope slides) by Sol-Gel process from ethanol and solution prepared by Zinc acetate as premonitormonoe then Diethanolamine as stabilizer and glacial acet homogenous as activator. The transparent and conductive, polycrystalline ZnO thin film was formed finally by dipping coating and spin coating conducted for film-plate on substrate, drying, pre-heat-treatment, anealing.A method using first principles and pseudopotentials based on density functional theory was applied to calculate the geometric structure and the band structure of ZnO doped with Ag. The calculations were carried out with a powerful package called Material Studio. And 32-atom supercells (2×2×2) were used to perform the total energy calculation. Some complexes of Ag bring deep acceptor level to the band structure of ZnO and the intrinsic defect of Zn will equalize the deep acceptor level. These will cause ideal P-type semiconductor difficultly to be prepared.But adopting Cu is very easy to be P-type semiconductor.X-ray diffraction (XRD), scanning electron microscope (SEM)were used to characterize the crystallization behavior, orientation and surface morphology of the ZnO thin films. It is revealed that the thin films with strongly preferred to the substrate surface which surface was homogenous,dense and crackfree was the crystalline phase of hexagonal wurtzite. The thin film was composed of plentiful meshy crystal. The average transmittance of thin film in visible region was above 80%. The optical band gap was widened with the increase of Ag/Zn molar ratio. The optimization parameter that is 17 layers,4% atm (Ag),180℃(pre-heating temperature),520℃(annealing temperature) was fished out by large numbers of experiment.

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