Effect Of Doping With Co And/or Sn On Crystal Structures And Properties Of ZnO Thin Films

ZnO is a type ofⅡ-Ⅵcompound semiconductor material with a direct wide band gap (Eg³.37 ev at room temperature) and a high excition binding energy of 60 meV. Its stable crystal structure is hexagonal wurtzite structure. ZnO possesses excellent heat conduction, electric conduction, chemical stability and ultraviolet absorption properties and can be used in many applications, such as surface acoustic wave devices, UV detectors, gas sensors, infra-red reflectors and solar cells and so on. Moreover, it has excellent optoelectronic properties, so ZnO is one of the most promising materials for optoelectronic devices in blue and ultraviolet region. With the rapid development of optoelectronic technology, the demand of the purple and blue short-wavelength light-emitting materials has become more and more imperative. Due to its energy gap of about 3.37eV at RT and high excition binding energy, ZnO can not only achieve blue and UV light emitting in theory, but also has remarkable low threshold value even above room temperature. So the investigations on the optical propertities and luminescence mechanism of ZnO become particularly important.In this thesis, the Co and/or Sn doped ZnO thin films were deposited on the glass substrate by means of sol-gel method. The influence of Co and/or Sn doping on surface morphologies and mircrostructures of ZnO films has been investigated by metallurgical microscope and X-ray diffraction (XRD). The XRD results indicate that all the ZnO samples show preferential orientation along (002) direction, and the Sn-doped ZnO thin film shows the best c-axis orientation and largest grain size. XPS results reveal that Co and Sn elements exist as Co²⁺ and Sn⁴⁺, testifying that Co and Sn ions have entered the ZnO crystal lattices successfully. The vibrating sample magnetometer (VSM) measures the ferromagnetic properties of Zn0.95Co0.05O thin films at room temperature. Strong blue double emission and weak green emission were observed in PL spectrum of all the samples. In addition, the ultraviolet peak appeared in the undoped and Co-doped ZnO thin films. Our results reveal that the Co and/or Sn doping can tune the band gap, meanwhile, such doping can also affect oxygen dislocation, zinc vacancy and zinc interstitial defect concentration. Finally, the possible luminescence mechanism of Co and/or Sn doped ZnO films were discussed.