Ion Implanted Preparation And Characteristics Of Indium Oxide-Based Diluted Magnetic Semiconductor Films

This thesis introduces the basic theories and the abroad application prospect of diluted magnetic semiconductors (DMSs). The structure and properties of In2O3 are introduced in this thesis as well as the applicatins of In2O3-based semiconductors due to outstanding optical and electric properties. The progress of transition metals (TMs) doping In2O3-based DMSs is subsequently reviewed. The main contents of this thesis are the studies of transition metal doped In2O3-based DMSs. And the dopant elements are chosen the ferromagnetic Fe ions and nonferromagnetic Cu ions in the preparation of In2O3-based samples. The Fe ions or Cu ions are implanted into the pure In2O3 films by Metal Vapor Vacuum Arc (MEVVA) ions source. Room temperature ferromagnetism (RTFM) appears after Fe or Cu ions implanted into pure In2O3 film samples.The effects of magnetic properties are examined by Superconductor Quantum Interference Device (SQUID) with different Fe ion implantation doses and annealing environments. The room temperature ferromagnetism is enhanced with the increasing ofFe ions implantation dose, no matter the implanted samples are annealed in vacuum or in O2. But the ferromagnetism is stronger when the samples are annealed in vacuum than those in O2 for the same Fe implantation dose. The additional oxygen vacancies (VOs) are detected in the samples annealed in vacuum by X-ray photoelectron spectroscopy (XPS). The additional VOs are beneficial for enhancement of ferromagnetism, especially for pure In2O3 films. The result shows that the saturation magnetization (Ms) of the pure In2O3 film annealed in vacuum is about 10 times larger than that annealed in O2, in which Ms is so weak that it can almost be neglected. The defects (the interface and surface defects), especially VOs, are responsible for the ferromagnetic properties. The Fe ions are substitutional dopants in In2O3 host matrix after Fe ions implanted. The bound magnetic polarons (BMPs) are formed by spin polarization of electrons neighbouring the Fe dopants under the intrinsic magnetic moment of Fe ions. The macroscopic ferromagnetism is originated from the ferromagnetic coupling interaction between the neighboring BMPs. The strong ferromagnetism coupling interaction occurs with the help of VO, which is like a bridge between the magnetic BMPs (Fe-Vo-Fe). Ihe antiferromagnetic couplings (Fe-O2-Fe) are destroyed by the additional introducing Vos, and are replaced by ferromagnetic couplings (Fe-Vo-Fe). This is the reason why the ferromagnetism of the samples annealed in vacuum is stronger than that annealed in O2.It is also studied the influence of the implanted ions’energy on the film’s magnetic properties. With the lower energy of the implanted ions, Fe ions are distributed in a shallower layer. And the concentration of implanted Fe ions is relatively higher in tower implantation energy than that in higher energy with the same implantation dose. So the room temperature ferromagnetism is enhanced by ferromagnetism coupling interaction between more magnetic BMPs. Moreover, the surface effect of the nano-scale films may bring more defects and may be responsible for the stronger room temperature ferromagnetism of the samples.The Cu ions are also implanted into pure In2O3 films as a comparison while the metal or oxide of copper is nonferromagnetic. Room temperature ferromagnetism appears after Cu ions are implanted into InO3 films. And the ferromagnetism is stronger for Cu implantation than Fe implantation with the same implantation dose and energy. However, the magnetic moment of Cu2+ is much less than Fe ions (Fe2+or Fe3+). The valence state of Cu ion is+2, and it acts like p-type doping and can produce hole carriers. The hole carriers are beneficial for expanding the range of ferromagnetism coupling interaction between BMPs, which formed by the hybridization of Cu 3d electrons and O 2p electrons. On the other hand, the projected range of Cu is shorter than Fe in In2O3 material with the same implantation energy. And the concentration of Cu is relatively higher than Fe in the dopant distribution areas with the same implantion dose and condtion. It’s reduced the distance between BMPs which are formed by spin polarization of electrons neighbouring the Cu dopants under the intrinsic magnetic moment of Cu ions. And more magnetic BMPs are involved in ferromagnetism coupling interaction. The aforementioned two facts are beneficial for enhancement of ferromagnetism when Cu ions are implanted into...