The Study On Preparation, Characterization And Properties Of Doped ZnO And SnO₂ Nanostructure Materials

In recent years, significant interest and desire have emerged for the wide-band-gapsemiconductors due to the needs in the optoelectronic devices which can be operate atextreme conditions (e.g. high temperature, high power, high frequence and strongradiation). In particular, zinc oxide (ZnO) is an oxide semiconductor with awide-band-gap of～3.2 eV, and the binding energy of the exciton is about 60 meV. It isstable at room temperature and has stong anti-radiation ability. ZnO has extensiveapplications and can be used in gas sensors, light emitting diodes, solar cells, fieldemission devices and transparent electrodes. The synthesis process of ZnO is facile andthe precursor materials are rich in the earth and low cost. The doping is an effectivemethod to modify the properties of ZnO. Tin dioxide (SnO₂) is another wide-band-gapsemiconductor (～3.6 eV), and the binding energy of the exciton is about 130 meV. SnO₂can be also used in many fields as ZnO mentioned above. Recently, SnO₂ attracted manyattentions of the researchers. Against the background of application of functionalmaterials ZnO and SnO₂, this article reports our research on ZnO and SnO₂ nanostructurematerials. The contents are as follows.1. Zr-doped ZnO nano thin films were deposited by radio frequency (RF) magnetronsputtering. The influence of Zr element on the structure, morphology and opticalproperty of ZnO films were investigated. Zr element was doped into ZnO matrix withdifferent contents. The optical band gap has blue shift as increasing Zr content. Andthe morphology of ZnO has much improved. The properties of annealed films werealso studied. The transmittance of the annealed samples (undoped and doped with 1.04at. %) was lower than 70%, but that of samples doped with more Zr element werehigher than 80%.2. Thin films of ZnO with different La doping concentration (0, 1, 3, 5, 10 at. %) arefabricated by sol-gel method using spin-coating technique. The effect of La dopingconcentration on the properties of ZnO films is investigated. The films are hexagonal wurtzite structure and have highly preferred growth along c-axis direction. However, itshows poor crystallization with increasing La concentration and the grain sizes of thefilms decrease remarkably. The optical transmittance of all films is higher than 85% inthe visible region, and doped films become more transparent. The optical energy gapincreases from 3.26 eV to 3.31 eV because some La ions have been incorporated intothe ZnO lattice. The surface chemical state of the films is examined by X-rayphotoelectron spectroscopy (XPS), and it is indicated that the La element exists mainlyas La(OH)₃ on the film surface.3. Hydrothermal method was used to fabricate undoped and Al-doped ZnO nanostructureson the ITO substrates which pre-coated with ZnO seed layers. The undopedwell-aligned ZnO nanorods were synthesized. When introducing the Al dopant, ZnOshows various morphologies. The morphology of ZnO changes from aligned nanorods,tilted nanorods, nanotubes/nanorods to the nanosheets when the Al dopingconcentrations increases. The Al doping concentrations play an important role on themorphology and optical properties of ZnO nanostructures. The possible growthmechanism of the ZnO nanostructures was discussed.4. The Eu-doped SnO₂ nanocrystalline powders were fabricated by sol-gel calcinationprocess. The effect of the Eu doping concentrations on the structure andphotoluminescence (PL) properties of Eu-doped SnO₂ nanocrystalline powders wasinvestigated. The samples display the reddish-orange light and the red light whenexcited at indirect and direct excitation, respectively. Meanwhile, PL spectra indicatethat the quenching concentrations are different when the excitation wavelength alters.Based on the analysis of the PL spectra, it is believed that Eu³⁺ ions located at differentsites in SnO₂ host are selectively excited. Further, the porous Eu-doped SnO₂ filmswere prepared by spin-coating method. The morphology of the film was dependent onthe calcination temperatures. The structure, morphology and PL property wereinvestigated. The formation mechanism of the porous morphology was also proposed.