| As micro electronic and integrated circuit technique developing rapidly, micro-electronics, which utilizes electrons as charge carriers and studies transport properties of devices, has been encountering a series of difficulties such as quantum effects and sharp increase in energy consumption per unit area of devices. In order to overcome these difficulties, a new subject Spintronics appeared in the1980s. Spintronics studies how to make use of the charge and spin of electrons simultaneously to solve the problems that micro-electronics suffers. The ideal material for spintronic devices should combine the energy band gap of semiconductors and spin sub-band splitting of ferromagnetic materials. Fortunately, diluted magnetic semiconductors (DMSs) prepared by doping common semiconductors with transition metal are discovered to satisfy the requirement of this new electronic device very well.In the past several decades, DMSs have attracted considerable interests due to their novel physical properties and potential applications in spin-based devices. Many material systems of DMSs, such as ZnO, TiO2, SnO2,In2O3, GaAs and GeMn, have been widely studied. Among various kinds of oxide DMSs, transition metal-doped In2O3has attracted great attention because of its excellent optical and electric properties, and its room-temperature ferromagnetism has been observed in Fe-, Co-, Ni-, and Cr-doped In2O3. Among these elements, Fe doping is particularly interesting and has attracted lots of attention because of the high solubility (as high as20%) of Fe ions into In2O3lattice and the high magnetic moment of the Fe3+ion, which makes Fe-doped In2O3a fascinating DMS. Many research works have been conducted on Fe-doped In2O3films, and high-temperature ferromagnetism was reported by several groups. Spin-polarized carriers were also revealed in this material by anomalous Hall effect (AHE). These results indicate that Fe-doped In2O3may be a promising ferromagnetic semiconductor for future spintronic devices. Therefore, this thesis chose Fe-doped In2O3films as the system of ferromagnetic semiconductor. Since Fe-doped In2O3films are very sensitive to growth methods and conditions, Fe-doped In2O3films prepared under different conditions always show very different physical properties. It is very important to study how the properties of Fe-doped In2O3films vary as preparation conditions. Meanwhile, improving structure, morphology, and other properties of Fe-doped In2o3films for application is necessary. Considering the two factors, in the thesis Fe-doped In2O3epitaxial films were deposited on YSZ substrates by PLD, to study the effect of three factors on properties of Fe-doped In2O3films:(1) Growth temperature of films;(2) Thickness of films;(3) Sn concentration in Sn and Fe-codoped In2O3films.Through systematical measurement and analysis, the following conclusions can be drawn.(1) As the Growth temperature increasing from450to800℃, the oxide secondary phases of Fe disappear gradually, and the intrinsic ferromagnetism of Fe-doped In2O3films is enhanced. Simultaneously, the crystal quality of films is improved, while the continuous surface of films has a trend to break up into separated islands and the conductivity of films decreases.(2) As the film thickness increasing from100to600nm, the structure and morphology of Fe-doped In2O3films are improved, but the properties in optics and electrics decline slightly. Dramatically, the easy axis of magnetization of films transforms from parallel to perpendicular to the film plane.(3) In Sn and Fe-codoped In2O3films, as Sn concentration increasing, the surface morphology, crystal structure, optical and transport properties of films are improved remarkably. No obvious change of the ferromagnetism of films by Sn doping is observed, which can be explained by a modified bounded magnetic polaron model. |
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