|Semiconducting properties of oxide thin films prepared by pulsed laser deposition
Pulsed laser deposition
Hong Kong Polytechnic University -- Dissertations
|Department of Applied Physics
|viii, 164 leaves : ill. ; 30 cm
|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 La0.7Sr0.3MnO3/Nb-lwt% doped SrTiO3 junction transport properties at room temperature. The La0.7Sr0.3MnO3 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.
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