| Project/Area Number |
14540304
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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 |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | OKAYAMA UNIVERSITY |
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Principal Investigator |
ARIMOTO Osamu OKAYAMA UNIVERSITY, Faculty of Science, Associate Professor, 理学部, 助教授 (70193092)
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| Co-Investigator(Kenkyū-buntansha) |
TANAKA Koichiro Kyoto University, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (90212034)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2003: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2002: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Keywords | Weakly electron-lattice coupling system / Exciton / Formation process / Relaxation process / Zinc diphosphide / Semiconductor / Phase relaxation / Exciton polariton |
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| Research Abstract |
In order to clarify the formation and subsequent relaxation processes of excitons, we have performed high- resolution modulation spectroscopy as well as ultrafast time-resolved spectroscopy for the exciton system in β-ZnP_2. The main results are summarized as follows.
1. Photoreflectance (PR) spectroscopy has been performed in order to investigate fine structure of the higher singlet exciton states. The PR spectrum shows clear structure at each exciton level with large modulation amplihtude. The mechanism by which the PR signal is produced is electroreflectance due to the periodic cancellation of the built- in surface electric field by photoexcited carriers. A high-resolution PR spectrum using a Ti: sapphire laser as a probe light reveals the higher members of singlet excitons up to n = 6.
2. Spectrally resolved degenerate four-wave mixing (FWM) spectroscopy has been done using a femtosecond laser. The FWM signal clearly exhibits a periodic ultrafast modulation as a function of the delay
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time between two excitation pulses. The modulation is assigned as the quantum beats due to the interference of two closely spaced transitions; the is free exciton and the bound exciton. Dephasing times T_2 of the is exciton polariton are measured at various energies between ET and EL, where ET and EL are transverse and longitudinal exciton energies, respectively. The T_2 is longer as the polariton energy is lower, suggesting that the phonon scatterings mainly govern the polariton dephasing.
3. Ultrafast reflectivity changes of exciton bands in (β-ZnP_2 have been investigated by pump-probe spectroscopy using a femtosecond laser. Spectrum of the pump-probe signal shows a significant negative reflectivity change in the energy range between E_T and E_L. Reflection relaxation time is 1.1 ps near E_L and 1.7 ps near E_T. These relaxation times are related to the acoustic phonon scattering of exciton polaritons. Transient reflectivity changes with a spectral shape of dispersion type are also observed at the energy where the excitonic molecule luminescence appears. Less
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