Transport Properties Of Perovskite Structure Manganese Oxide Films And Heterojunctions And Its Photoinduced Effect Study

Doped manganese oxides with a perovskite structure have been a focus of intensive studies due to their rich physics properties and potential applications in spintronic devices. In this dissertation, the La2/3Sr1/3MnO3-δ(LSMO) films and many kinds of manganite-based heterojunctions are chosen to study their electric-magnetic transport and photoinduced effect systematically. The main contents and research results are concluded as follows:1. Many mangaite films have been fabricated by using dc-magnetron sputtering. High-quality c-axis-oriented La2/3Sr1/3MnO3-δ(LSMO) films have been grown directly on Si (001) wafers by dc-magnetron sputtering without prechemical treatment of the substrate surface.2. The photoconductivity of manganite films has been studied carefully. Both transient and persistent photoconductivity (abbreviated to TPC and PPC, respectively) are observed in oxygen-deficient (LSMO) thin films at low temperatures. The influence of bias current on resisitivity and photoconductivity in oxygen-deficient La2/3Sr1/3MnO3-δthin films has also been investigated. Moreover, it is found that a small magnetic field can erase most of PPC effect sharply.3. The electric transport character in heterojunctions composed of a La0.7Ce0.3MnO3 film and Nb-doped SrTiO3 substrate (LCEM/STON) is investigated. It is found that there exists a variation of reverse transport mechanism from ionization to tunneling at T=175 K. Moreover, a crossover from negative to positive magnetoresistance (MR) is observed in the LCEM/STON. The temperature and bias current dependences of MR sign in the junction are investigated carefully. We attribute the appearance of the positive MR at higher temperatures to the tunneling transport mechanism.4. The manganites/SiO2/Si p-i-n heterojunction with good rectifying property is fabricated. The transport mechanism in different conditions has been investigated. It is found that there is quite different between transport properties above and under Curie temperature of the heterojunction. Moreover, huge photoconductivity was found in this kind of manganite based heteojunctions.5. Photovoltaic effects in heterojunctions composed of manganite film and Nb-doped SrTiO3 substrate were investigated. The strong temperature-dependent photovoltaic effects have been observed and the effect of magnetic field on photovoltaic effect (PVE) has been investigated in the heterojunction.