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Title: Semiconducting properties of oxide thin films prepared by pulsed laser deposition
Authors: Lam, Ching-yee
Keywords: Thin films
Pulsed laser deposition
Hong Kong Polytechnic University -- Dissertations
Issue Date: 2005
Publisher: The Hong Kong Polytechnic University
Abstract: All oxide p-n junctions have been successfully grown by pulsed laser deposition method. Three different p-n junctions, namely LaxSrxMnO₃/SrTiO₃/La1-ySryTiO₃, La₀.₇Sr0.₃MnO₃/Nb-1wt% doped SrTiO₃ and Li₀.₁₅Ni₀.₈₅O/La₀.₀₅Sr₀.₉₅TiO₃ have been fabricated. Structural characterization by x-ray diffraction reveals excellent heteroepitaxial relation in all these junctions. The diffusion potential of La1-xSrxMnO₃/SrTiO₃/La1-ySryTiO₃, La₀.₇Sr₀.₃MnO₃/Nb-lwt% doped SrTiO₃ and Li₀.₁₅Ni₀.₈₅O/La₀.₀₅Sr₀.₉₅TiO₃ junctions are 1eV, 0.2eV, and 0.3eV respectively. All of the fabricated p-n junctions yield typical I-V characteristics and display good rectifying property under room temperature. According to the high thermal stability property of oxides, all-oxide p-n junction could operate at temperature up to 500K. Throughout the research, it is observed that even a highly conducting and metallic-like oxide film could form good p-n junction. However the narrow depletion layer causes a large leakage current under the reverse biased condition. The insertion of insulating layer (SrTiO₃) helps in "broadening" the depletion layer and hence prevents the occurrence of large leakage current. Unfortunately the turn-on voltage increases as well. So a compromise between the reduction of leakage current and the increases of turn-on voltage should be made. It is consideration that ultimately determines the optimum insulating layer thickness. The high temperature operation (~500K) has been confirmed in all junctions. In general, the change in leakage current and turn-on voltage of all-oxide p-n junctions follow the same pattern as those seen in conventional semi-conductor counterparts. La₀.₇Sr₀.₃MnO₃ is a well known magnetoresistance material. It exhibits a large positively MR. We have studied influence of the magnetic field on the La₀.₇Sr0₃MnO₃/Nb-lwt% doped SrTiO₃ junction transport properties at room temperature. The La₀.₇Sr0.₀.₃MnO₃ film, which is grown at 100mTorr, has the phase transition at 290K. It has been shown that the junction works stably upon a 1T magnetic field application. No apparent spin dependent junction transport properties have been observed. Photo-response has been investigated for the all-transparent oxide Li₀.₁₅Ni₀.₈₅O/La₀.₀₅Sr₀.₉₅TiO₃ junction as well. This junction potentially can act as a UV photo-detector. The highest photo-response occurs at 340nm. The junction provides a photovoltage of 377mV under 1.28mW UV illumination.
Description: viii, 164 leaves : ill. ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577M AP 2005 Lam
Rights: All rights reserved.
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