Preparation And Magnetic, Transport Properties Of Fe-doped Indium Oxide

Microelectronics, which is a branch of electronics, mainly studies and utilizes the transport properties of electron as a charge carrier in solid materials in order to realize the signal processing. In conventional microelectronic, electron was simply seen as a carrier of charges. However, the spin of electron barely caught attentions. As the degree of integration increases, the device size enters into nanoscale, in which the energy consumption per unit area rises rapidly and results in serious heat injury problems. Furthermore, the quantum confinement effect will play a leading role, which makes the theory of energy band useless. In order to solve those problems, researchers begin to pay attention to spin which is also an intrinsic property of electron. They expect to realize the utilization of both the charge and the spin and develop a new generation of electronic device. This new kind of device has more advantages such as faster arithmetic speed, smaller size, lower energy consumption, information preservation under power-off and potential applications in quantum computation than the former one. This new research area named spintronics, is an important direction for future information technology development. To realize the goals of spintronics, the most important mission is to develop a new material which possesses both the band-gap of semiconductor and spin sub-band splitting of magnetic material simultaneously. Ferromagnetic semiconductor is just a kind of this new material. In the late 80s, Fert and Grunberg discovered the Giant Magneto-Resistance, which lead to a revolution in magnetic storage and record, making a great development of massive application of computers in the 1990s. From then on, spintronics has become the hotspot of science community. Spintronics, as a new branch, studies, utilizes and controls the electron transport of spin polarization.The preparation method of typical ferromagnetic semiconductor is doping transition element into the current semiconductor system. It is expected that the transition element may enter the crystal lattice by substituting cations'positions, and through the ferromagnetic coupling between transition metal ions, ferromagnetism may appear in semiconductor on the basis of the original band-gap. In 1990s, Ohno et. al. successfully doped Mn element into GaAs. This material can not be used because of the low Curie temperature which is only 170K. In the year of 2000, based on the traditional Zenner model, T. Dietl et. al. calculated and predicted a Curie temperature of higher than 300K in Mn doped wide band-gap semiconductors such as GaN and ZnO. After this report, many researches have been done. The most studied systems are ZnO and TiO2. However, results reported are different or even contradictory among different teams. Until now, the question that whether transitional element doped oxide systems has intrinsic ferromagnetism is still inconclusive. Meanwhile, many groups have reported the existence of ferromagnetism, and some have even revealed unique properties such as anomalous Hall effect. And the solubility of iron in In2O3 is as high as 20%. In addition, with a view to the excellent opto-electric and gas sensitive properties of In2O3, we choose Fe-doped In2O3 as the study system of this thesis, make samples with high quality and discuss their magnetism and transportation.The samples were prepared by PLD (pulse laser deposition) on (100) (110) (111) YSZ substrates. RHEED was used to monitor the surface of samples during the growth. AFM and XRD are also used to characterize the structure of samples after growth. The results showed the samples were expitary growth on substrates. Magnetism of samples was measured using the SQUID system. Analysation of the MH curves shows that samples have room temperature ferromagnetism which changes with temperature. Little or none anisotropy is found, which is opposed to the reported results. Transportation qualities were measured using Van der Pauw method in the condition provided by SQUID. Figures of concentration vs T, mobility vs T and resistance vs T were drawn according to the measurement. Room temperature Abnormal Hall Effect demonstrated the intrinsic ferromagnetism of samples. Discussion about the transportation qualities showed there might be more than one kind of carriers in the samples.In conclusions:epitaxy Fe doped In2O3 thin films have been produced by PLD system on (100) (110) (111) YSZ substrates. RHEED, XRD, AFM measurements show the samples are epitaxy. Room temperature ferromagnetism is realized, which is demonstrated by the room temperature Abnormal Hall Effect. The transportation of samples is also discussed, which shows more than one kind of carrier might exit in the samples.