1999 Fiscal Year Final Research Report Summary
Electron dynamics in semiconductor quantum structures investigated by time-resolved terahertz spectrosccopy
| Project/Area Number |
09450138
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
電子デバイス・機器工学
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| Research Institution | The University of Tokyo |
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Principal Investigator |
HIRAKAWA Kazuhiko Institute of Industrial Science, The University of Tokyo, Associate Professor, 生産技術研究所, 助教授 (10183097)
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| Co-Investigator(Kenkyū-buntansha) |
ARAKAWA Yasuhiko Research Center for Advanced Science and Technology, The University of Tokyo, Professor, 先端科学技術研究センター, 教授 (30134638)
SAKAKI Hiroyuki Institute of Industrial Science, The University of Tokyo, Professor, 生産技術研究所, 教授 (90013226)
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| Project Period (FY) |
1997 – 1999
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| Keywords | Terahertz radiation / femtosecond / tunneling effect / Plasma oscillation / Quantum beat / nanostructures / Ultrafast spectroscopy / Velocity overshoot |
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| Research Abstract |
Knowledge on the electron dynamics in semiconductor quantum structures is indispensable for realization of ultrahigh speed electron devices which operate in the terahertz (THz) frequency range. Since ultrafast electron motions accompany radiation of electromagnetic waves, information on the dynamical motion of electrons can be investigated by measuring the radiation in the time domain (time-resolved THZ spectroscopy). We have investigated the electron dynamics and coherence of motions by using this technique. The major results obtained in this projects are ;
(1) When two quantum wells are coupled quantum mechanically, electron moves back and forth coherently between the two quantum wells via tunneling effect ("quantum beat"). We have successfully detected the oscillatory THz radiation due to the quantum beats of electrons and determined the decay time of the coherent tunneling to be 6 ps at low temperatures.
(2) We have investigated the dynamics of two-dimensional free carrier plasma oscillations in selectively doped quantum wells. It is found that there are two distinctive excitation mechanisms of the 2D plasmons; coherent impulsive stimulated Raman process and incoherent sudden heating by photoexcited carriers.
(3) We have built up a THz detection system with 20 THz bandwidth and 50 fs time resolution by using a correlation measurement technique. By using this system, we have investigated the nonequilibrium electron transport in GaAs depletion regions. It is found that within 700 fs after the acceleration electrons are in a velocity overshoot mode and that photoexcited electrons coherently excite optical phonons.
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