Optical And Magnetic Properties In ZnO Based Diluted Magnetic Semiconductors

There has been a great interest to develop new materials which exhibit semiconductor and ferromagnetic properties, known as diluted magnetic semiconductors (DMSs). Besides their"charge,"the ferromagnetic semiconductors possess an additional degree of freedom and functionality of"spin,"which can be integrated into the existing semiconductor devices, important for applications in spin electronics and magneto-optics. Diluted magnetic semicondutors consist of non-magnetic semiconducting materials doped with a few at.% of impurity magnetic cations of transition metal or rare earth. As for application, it is vital to prepare samples with higher Curie temperature and bigger saturation magnetization. Recently, Having ferromagnetism or not in the samples, the origin of ferromagnetism, and exchange mechanism in transition metal doped ZnO remain a very controversial topic. Therefore, it is necessary to study the property of the Ni doped ZnO powders prepared using sol-gel , Fe doped ZnO films and Ni doped ZnO films using magnetron sputtering. The results are as following:1. Zn1-xNixO ( x=0.1%, 0.4%, 0.7%, 1.0% ) powders were prepared using sol-gel technique, and investigated the structure, optical, and magnetic properties in samples. X-ray diffraction measurements have shown that all samples have wurtzite structure. X-ray photoelectron spectroscopy studies indicate the doped Ni ions are in divalent states in all samples. Optical absorption spectra shows that the band energy of Zn1-xNixO powders decrease with increasing of Ni concentration. The room temperature ferromagnetism are observed in all samples and the saturation magnetization increase, as the Ni concentration increases. Photoluminescence measurements of Zn1-xNixO illustrated a broad peak at a wavelength centered at about 467 nm has also been observed which indicates the presence of a greater fraction of defect in ZnO. The ferromagnetism being intrinsic is related to effective doped ions and defects.2. The room temperature ferromagnetism is observed in Ni doped ZnO films prepared using magnetron sputtering. The curie temperature is well above 340K, the saturation magnetization first increases and then decreases as the Ni concentration increases in films. The Ni ion is in a +2 charge state in films. No secondary phases or metal clusters are found in films, which confirm ferromagnetism is intrinsic. Correspondingly, Ferromagnetism is observed in Zn0.97Ni0.03O films grown under different atmospheric ratios of argon to oxygen. The results show that as the fraction of oxygen in the atmosphere increases, both the saturation magnetization and the blue emission induced from oxygen vacancies decrease, and the resistivity increase, which confirm that the ferromagnetism is correlated with the oxygen vacancy level.3. The studies of the structure, charge state, and surface morphology in Zn1-xFexO show that the Fe ions are in +2 charge state in Zn1-xFexO thin films with a wurtzite structure. No secondary phases or clusters are observed. Magnetization measurement shows all samples have the room temperature ferromagnetism, The curie temperature is well above 340K, the saturation magnetization first increases and then decreases as the Ni concentration increases in films. The sample have the obvious magnetic domain and magnetism anisotropy which indicate that ferromagnetism is intrinsic and related to the defects in all samples. The Zn0.88Fe0.12O thin film annealed in the air only has paramagnetism. Moreover the electronic resistivity increased by 2 orders comparing with the Zn0.88Fe0.12O thin film annealed in the vacuum. It induced that the ferromagnetism is related to oxygen vacancy.