Investigation Oil Hydrothermal Synthesis, Doping And Properties Of ZnO

ZnO is a new Ⅱ-Ⅵ compound semiconductor with a wide band gap and a large excitonbinding energy and is widely used in the field such as lighting emitting diode （LED）,piezoelectric components, diluted magnetic semiconductors （DMS）, due to their piezoelectric,optoelectric and mageticelectro properties. Transition metal-doped ZnO semiconductors havenovel gas, pressure and magnetic sensibility, which provide an opportunity for fabricatingnew sensors and DMS components. DMS materials have Giant magnetoresistance （GMR）effect, Faraday rotation, enhanced magneto-optical effect, etc., and are the most promisingcandidates for their potential applications in the field of magnetic induction components,spinning transistor, ultradense nonvolatile semiconductor memory. All the same, there are stilldemands for intensive studies on P-type doped ZnO, ferromagnetics at room temperature,stable luminescence of monochromatic light etc.In this paper, ZnO nano array is fabricated by hydrothermal process, and the effect ofprocess parameters and the concentration of dopants on structure, morphology, luminousspectra and magnetic properties is investigated. Nitrate zinc, hexamethylene tetramine （HMT）,acetate colbium, nitrate nickel, acetate zinc, ethylene glycol, and ethanolamine are chosen asraw materials. Phase composition, crystallization and preferred orientation of array films areanalyzed by XRD. Microstructure and crystal morphology of array films are characterized bySEM. Microstructure change of ZnO array films with Ni²⁺and Co²⁺concentration is analyzedby Raman spectra. Internal defects and luminous properties are analyzed byphotoluminescence （PL） spectra. Ferromagnetic properties at room temperature are measuredby magnetic hysteresis loops. The main contents in this paper are as following.（1） Investigation on hydrothermal process of ZnO nano array films. The effect of agingtime on buffer layer, then on structure and morphology of subsequent hydrothermal ZnOarray films, is investigated. Grain refinement and uniformity of buffer layer increase withaging time, which results in decreased diameter, increased orientation, even and densedistribution of ZnO nano rods. ZnO nanorod array films with good crystallization andpreferred orientation, regular shape and orthohexagonal tip are obtained via suitablelyincreasing hydrothermal temperature, hydrothermal time and the concentration of [Zn²⁺].（2） Investigation of Ni²⁺doping on ZnO array films. The effect of doping content of Ni²⁺and hydrothermal condition on morphology, structure and PL spectra, magnetic properties ofZnO array films is studied. Microstructure change of ZnO array films is analyzed by Raman spectra, and possible mechanism is discussed. A small quantity of Ni²⁺ions can enter ZnOcrystal and substitute partial Zn²⁺ions, which will improve the growth of ZnO nanorods, butwon’t change their growth mechanism. Partial Ni²⁺ions may form some organic substancewith HMT and CH3COO-. In the solution and such organic substance will attach on thesurface of ZnO tips, which will hinder the polar growth of ZnO nanorods and destroyhexagonal structure. Improved crystallization and saturation magnetism, decreased crystaldefects are achieved by suitable amount of Ni²⁺doping.（3） Investigation of Co²⁺doping on ZnO array films. The effect of doping content of Co²⁺on morphology, structure and PL spectra, magnetic properties of ZnO array films is studied,and possible mechanism is discussed. Although Co²⁺doping has similar effect on ZnO filmsas Ni doping, it is difficult for Co²⁺ions entering ZnO crystal and substituting Zn ions, andmost Co²⁺ions exist in the solution. The morphology of ZnO epitaxy films could be adjustedvia changing the concentration of Co²⁺ions. Hydrothermal ZnO films evove from orientednanorods arrays to close-packed grains with irregular polygonal structure. The epitaxialgrowth of ZnO films almost stops when the concentration of Co²⁺x>0.025M due toincreasing internal stress. Saturation magnetization and coercive strength decrease with Codoping content.