Probing optical-phonon propagation in GaAs/Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As quantum-well samples via their nonequilibrium population
- Department of Physics, University of California, Berkeley, California 94720 (United States)
- Department of Physics, Seoul National University, Seoul 151-742 (Korea)
- Korea Institute of Science and Technology, Cheongryang, Seoul 136-791 (Korea)
- Spectroscopy Laboratory, Korea Research Institute of Standard and Science, Taejon, 305-606 (Korea)
- Department of Physics, California State University, San Jose, California 95192 (United States)
- Department of Physics and Center for Laser Research, Oklahoma State University, Stillwater, Oklahoma 74078 (United States)
We develop a theoretical model to analyze a nonequilibrium optical- (LO-) phonon population by Raman scattering in GaAs/Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As quantum wells. With the assumption of bulklike hot-electron relaxation, the effect of LO-phonon confinement on a nonequilibrium optical-phonon population (NOP) is isolated. Our analysis shows that the decrease in spatial extent or coherence length of LO phonons is reflected by a decrease in NOP. This is because the contributions from large {ital q} wave vectors with small occupation numbers dominate as the spatial extent decreases. Our method is applied to explain picosecond Raman-scattering experiments on GaAs/Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As. The increasing NOP with decreasing {ital x} is interpreted as the result of an increase in the coherence length of LO phonons, since for smaller {ital x}, the Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As barrier is no longer effective in localizing GaAs LO phonons within the well. Using this model, we also deduce coherence length of LO phonons as a function of {ital x}. Our results show that for values of {ital x} between 0.2 and 0.4, the GaAs LO phonon in GaAs/Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As quantum wells changes from a bulklike propagating mode to one localized within the wells. {copyright} {ital 1996 The American Physical Society.}
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 389305
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 54, Issue 15; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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