Study On Rectifying Current-voltage Characters And Transport Properties Of La_0.8Sr_0.2MnO₃Thin Films Hetero P-n Junctions

The studies of perovskite manganese oxides have attractedmuch renewed attention in strongly correlated electron system since the discovery of colossal magnetoresistance (CMR) effect in the mid-1990s. Because CMR effects are great valuable in industrial demand, such as the magnetric memory, magnetic random access memeries, magnetic sensors and the spin-polarized dependent of all oxide devices; however, these demands mainly depend on theproperties of the thin-films. As a fundamental physics research, the manganite system exhibits many intriguing physical behaviors; e.g. paramagnetic-ferromagnetic transition together with insulator-metal transition, charge-orbital ordering, phase separation, Jahn-Teller distortion and the coupling between them; especially, the investigation in the manganite films not only have important significance for the spintronic application, but also stimulate the great progress in the growth of epitaxial thin films for all oxide or oxide-metal device.In this thesis, the influence of the lattice-misfit strain and oxygen contents on the thickness effects of CMR manganite thin films was carefully investigated.Specially, the in-situ deposition oxygen pressure affects on the structural, rectifying current-voltage characters and transport properties of the ultra-thin films, and effects of the angle-distortion induced strain on the transport behavior of epitaxial thin films is also studied in details.The whole thesis consists of four chapters.In Chapter1:The current research status of manganese oxide film, physical properties and semiconductor theory are given. First we reviewed the perovskite structure basic properties of manganese oxide and the main features, including crystal structure,electronic structure, exchange action, phase diagram, rectifying current-voltage characters and Hall effect.In Chapter2:The preparation of manganese oxide and bulk preparation methods, pulse laser deposition methods and characteristics are briefly introduced. We systematically introduced doping manganese oxide (LSMO) heterojunctions (thin films) preparation of parameters,the structure and characterization of rectifying current-voltage characters. And the measurement instruments and basic principle are introduced in brief.In Chapter3:Heteroepitaxial junction composed of La0.8Sr0.2MnO3(LSMO) and the(100)0.7wt%Nb:SrTiO3(NSTO)has been fabricated by pulsed-laser deposition. The effect of the in-situ deposition oxygen pressures and the shelve time after annealing in vacuum on the structure and the rectifying current-voltage behavior of the LSMO/NSTO(100) heteroj unctions was carefully studied. The experimental results indicate that, LSMO films on NSTO(100) substrate have a good single crystal structure and flat surface, and shows good rectifying current-voltage characters. All of these indicate the LSMO/NSTO film heteroj unctions canbe applied to microelectronics devices.In Chapter4:The La0.8Sr0.2MnO3(LSMO) epitaxial films on LSATand STO have been fabricated by the pulsed-laser deposition. The influence of the substrate strain, oxygen contents and the thickness on structure and transport properties of manganite oxide thin film was carefully investigated. The experimental results show that, metal-insulator transition temperaturesTp increasewith the decrease of the film thickness, and overall resistance rate increases.