2004 Fiscal Year Final Research Report Summary
Theory of coherent collective excitations in semiconductor superlattices excited by ultrashort optical pulses
| Project/Area Number |
14540297
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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 | Japan Advanced Institute of Science and Technology |
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Principal Investigator |
KATAYAMA Shin-ichi Japan Advanced Institute of Science and Technology, School of Materials Science, Professor, 材料科学研究科, 教授 (30018270)
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| Project Period (FY) |
2002 – 2004
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| Keywords | quantum wells / coherent oscillations / intra-miniband plasmon / intersubband plasmon / intersubband transition / THz radiation / GaAs p-i-n diodes / Raman laser |
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| Research Abstract |
We have explored coherent oscillations in semiconductor superlattices (multiple quantum wells : MQWs) excited by ultrashort pulse lasers, and have studied generation mechanism of electromagnetic waves (including a laser) in a terahertz (THz) regime associated with the collective excitations. Our results are summarized as follows :
(1)We have explored the coherent intra-miniband plasmon in a superlattice, which propagates along the growth axis. To compare our results with the observed THz radiation as well as reflective electro-optical sampling data, we have constructed a dielectric response theory based on density matrix. Using Kronig-Penney model, and changing ratio of well width to barrier width, we evaluated the plasmon dispersion relation. Our results indicate the discrete nature of plasma frequency as a function of electron number in multi-minibands, and correspond well to the observed appearance and disappearance of THz radiation from AlGaAs/GaAs superlattices.
(2)We simulated THz radiation by coherent LO phonons as well as ultrafast movements of non-equilibrium photoexcited carriers in GaAs p-i-n diodes under high electric field. So we revealed an importance of synchronization between LO phonon and overshoot of carriers for generation of coherent LO phonon oscillation, and have predicted a saturation behavior of THz radiation intensity under extremely strong electric fields above 150 kV/cm.
(3)We have constructed a theory of THz Raman laser excited optically in asymmetric coupled double quantum wells (ACDQWs). A stimulated Stokes Raman scattering due to collective inter-subband plasm on produces the proper laser gain in this structure. Further, it was revealed that the interaction of coherent intersubband plasmon with LO phonons plays the key role for a determination of the laser frequencies. Our results explain well the observed laser frequency in AlGaAs/GaAs ACDQWs.
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