ZnO Doped Co-Based Diluted Magnetic Semiconductors By Pulsed Laser Deposition

In this paper, the diluted magnetic semiconductor (DMS), referred to as semiconductor alloys in which some atoms of II-VI, IV-VI and III-V semiconductors are randomly substituted for by magnetic atoms, are promising novel materials for spintronics since they have charge and spin degrees of freedom in a single substance. Dilute magnetic semiconductors focus on possible spin-transport property, which has many potentially interesting device applications, such as spin-valvetransistors, spin light-emitting diodes, non-volatile memory, logic devices, optical isolators and ultrafast optical switches.In this thesis we introduced the development and recently results about the DMS. Based ZnO, and prepared the Co-doped ZnO targets and films using the solid state reaction and pulsed laser deposition (PLD). The optics, electronics, magnetics and the structural properties of material have measured. The experiment relation of the material properties and the methods and technology of preparation are investigated. The main research contents are as follows:(1) ZnO thin films were deposited on sapphire (0001) substrates by a high-purity ZnO target and a pulsed Nd:YAG laser with a wavelength of 355nm. The structural, optical and electrical properties of ZnO thin films were grown and investigated in various substrate temperatures. The morphological property of the films was analyzed by atomic force microscopy (AFM). The optical and electrical properties of the films were tested by Raman scattering and ultraviolet photoluminescence (PL) emission and Fourier transformed infrared spectrum (FTIR), Hall-effect measurements, respectively. The experimental result of the substrate temperature is an important parameter to influence the film morphology and films grown, the high quality crystallinity has an excellent UV emission at 500℃.(2) Zn0.9Co0.1O bulks were compounded by the solid state reaction at various fritting temperatures. Zn0.9Co0.1O bulks were synthesized in order to investigate the structural and optical properties of the bulks. The structural properties of a nubby powder was measured by X-ray diffraction(XRD) analyzer. The valence electron and doping concentration of bulk was measured by X-ray photoelectron spectroscopy(XPS) analyzer. Some basic properties of the bulk powder materials were tested in order to contribute to the comprehension of the development of magnetism in the semiconductors. The corresponding magnetic properties were evaluated by field-cooling and zero-field-cooling magnetization measurements. The optical properties of the target were tested by Raman scattering and FTIR and ultraviolet photoluminescence (PL) emission measurements, respectively. The results deduced that Co ions are well inserted in the ZnO structure and are surround by four oxygen. It means that a series of Co will substitute Zn and the sample retain original structure in wurtzite lattice with a temperature of 1200℃, then lead to chemical bond formation of Co-O, at the same time, the band gap of ZnO crystal lattice will be narrowed from the Raman spectrum has presented.(3) Co-doped ZnO films of Diluted magnetic semiconductor prepared in various temperature by PLD. Co:ZnO films were synthesized with different substrate temperatures in order to investigate the structural optical electric and magnetic properties of the films. The film structural properties were measured by AFM and X-ray diffraction(XRD) analyzer, respectively, a series of Co will substitute Zn and the sample retain original structure in wurtzite lattice with a temperature of 500℃and more even than no-doped ZnO films. Although mostly the Co:ZnO films possess a common feature that Co2+ replaces Zn2+ by XPS, the content of Co increased with temperature higher, and the film appears Co cluster phenomenon with 800℃. The optical properties of the samples were tested by UV-visible absorption measurements that the results deduced from the band gap of ZnO crystal lattice will be broadened in the UV-visible absorption has presented. Because the electrics and magnetics properties of Co:ZnO films is strongly dependent on the substrates, carrier concentration and p-n types is being change obviously. In the meantime, the effect of magnetic properties with doping concentration is a down to openings parabolas.