Preparation And Properties Of ZnO Based Diluted Magnetic Semiconductor Materials

As a new kind of semiconductors, diluted magnetic semiconductors (DMSs) make use of the spin of electrons in addition to their charge and therefore have characteristic of both magnetism and semiconductor. Due to their performance of magnetism, magneto-optical properties, magnetoelectricity and so on, DMSs materials can be employed for a variety of applications, such as spinpolarized electronic devices and optoelectronics field. In recent years, ZnO, as a wide band gap semiconductor, has attracted considerable attention to the development of DMSs with perfect performance due to its good features, such as high exciton binding energy (60 meV), better temperature stability, high transmittance, high chemical stability, abundant raw materials readily available, and transition metal ions easy-doping.In this thesis, the transition elements doped ZnO-based diluted magnetic semiconductor thin films and nanomaterials were selected as the research objects and Co, Cr, and Ni doped ZnO-based DMSs were successfully prepared with magnetron sputtering and hydrothermal methods. The effects of various process parameters on the structures and properties of ZnO-based DMSs were studied and the origin of the magnetism was also investigated. It is expected to obtain ZnO-based DMSs thin films and nanomaterials with excellent performance, which will lay a basis for further practical application. Specific study as follows:(1) Zn1-xCoxO DMSs thin films deposited on Si(100) substrate were prepared with RF magnetron sputtering method. The effects of preparation parameters, such as working pressure, deposition temperature, gas ratio, and annealing temperature on the structure, morphology and properties of thin films were studied detailed. The results showed that the samples are hexagonal wurtzite structure, and have good c-axis orientation. Co cations are in the +2 oxidation state and that Co2+ is incorporated into the wurtzite lattice at Zn2+ sites. M-H curves indicate that the samples exhibit room temperature ferromagnetic behavior, which is the intrinsic quality of the samples. The presence of oxygen vacancies induced the appearance of ferromagnetism for the Zn1-xCoxO samples.(2) On the basis of the Zn1-xCoxO films, the structure and magnetic properties of Co-N co-doped ZnO DMSs thin film were further studied. The structure analysis shows that the sample remains hexagonal structure and doping of the N element has little effect on its structure. Magnetic analysis showed that Co-N co-doped into the films improved the saturation magnetization of the samples, which implies that N element is beneficial to increase magnetic properties.(3) Zn1-xCrxO nanomaterials were prepared with hydrothermal method and the effects of parameters including reaction time, reaction temperature, and Cr contents on structure, morphology and properties of the Zn1-xCrxO nanomaterials were investigated detailed. The results show that the parameters have has great effect on the crystallinity and morphologies of the samples. The optimality reaction conditions were proved as 140℃and 13h. With the increase of reaction time, the intensity of diffraction peak increases first and then decreased, and the morphology of the samples changed from rod-like to sheet. As the reaction temperature increased, the crystallinity increased. The rod structure of the samples will be destroyed seriously with increasing of Cr doping content. All the Zn1-xCrxO samples show obvious ferromagnetic at room temperature, which can be considered as the intrinsic quality of the Zn1-xCrxO samples. With increasing of Cr doping content, Ms increases first and then decreases. PL spectra indicate that suitable amount of Cr content is helpful for improving photoluminescent property of ZnO.(4) Zn1-xNixO nanomaterials were prepared by hydrothermal method and the effects of reaction time, CTAB concentration and Ni doping content on the structure and magnetism of the samples were studied. With increasing of reaction time, the crystallinity decreased and the morphology of the samples changed from rod-like to sheet. The content of CTAB has little effect on the structure and morphology of the samples. The samples show obvious ferromagnetic at room temperature, which can be considered as the intrinsic quality of the Zn1-xNixO samples. The magnetic properties are enhanced with increasing of Ni doping content and decreased with prolonging the reaction time.