2007 Fiscal Year Final Research Report Summary
Study on photogenerated carriers and their relation with novel photoinduced properties of transition-metal oxides
| Project/Area Number |
17540298
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics I
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| Research Institution | Wakayama University |
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Principal Investigator |
ITOH Chihiro Wakayama University, Faculty of Systems Engineering, Professor (60211744)
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| Co-Investigator(Kenkyū-buntansha) |
KIDA Hirotsugu Wakayama University, Faculty of Systems Engineering, Associate Professor (30186275)
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| Project Period (FY) |
2005 – 2007
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| Keywords | photogenerated carriers / numn mrobe-interferometry / steady state photoconductivity / Strontium Titanate / anatase / lead tangstate |
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| Research Abstract |
We have studied properties of photogenerated carriers in transition-metal oxides such as strontium titanate (SrTiO_3), anatase type crystal of titanium dioxide (a-TiO_2), and lead tungstate (PbWO_4) by means of fs-time-resolved interferometry and photoconductivity measurements. We obtained following results:
(1) Pump-probe interferometric study revealed that the photogenerated carriers in SrTiO_3 are free at 4 K. The lifetime of the carriers was much longer than 80 ps, which is the time separation between the probe pulse pair for detecting phase shift induced by the pump pulse. The extraordinary long lifetime is compatible with large drift mobility obtained by the time-of-flight transient photoconductivity measurement.
(2) We found that the photocurrent of PbWO_4 was resolved into two components with considering its temperature dependence. The excitation spectrum of the component related to the intrinsic carriers showed a peak at 4.15 eV and a rise around 4.7 eV. These structures are presumably ascribed to the excitonic and the direct band-to-band transitions. However, the excitation spectrum of the carriers thermally released from trapped states shows a peak at 4.12 eV. The excitation spectrum of the latter component is identical to that of the G (II) luminescence.
(3) Photocurrent measurement with using a sample sandwiched by transparent blocking electrodes revealed that the excitation spectrum of the photoinduced charge showed a peak at3.9 eV, as well as the 4.1 eV peak found by the ordinary photoconductivity measurement.
(4) Photoinduced AC conductivity measurements revealed that photocurrent of a-TiO_2 was composed from frequency-independent (DC) and frequency-dependent (AC) components. The AC component showed power low dependence on the field frequency. While the DC component is arising from free carries, the AC component is conceivably due to polarons. The DC component was excited efficiently above 3.4 eV, which is much larger than the band-gap energy of a-TiO_2.
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Research Products
(13 results)
