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Titre du Document
Ballistic phonon production in photoexcited Ge, GaAs, and Si
Auteur(s)
MSALL M. E. ; WOLFE J. P.
Résumé
Phonon imaging and photoluminescence measurements are used to determine the frequency and spatial distribution of optically generated nonequilibrium phonons in Si, Ge, and GaAs at 1.7 K. At low excitation levels the thermalization of photoexcited carriers and the subsequent phonon down-conversion produce a broad frequency distribution of acoustic phonons that "quasidiffuse" in the crystal. These phonons produce a temporally broad heat pulse when detected at a distance from the excitation point. At moderate excitation levels (typically a 10-nS pulse with a power density of ∼20 W/mm2), the laser pulse produces a dense electron-hole plasma that can radically change the frequency distribution of nonequilibrium phonons. The plasma is a potentially rich source of low-frequency acoustic phonons, characterized by a temporally sharp heat pulse at a remote detector. The fraction of low-frequency phonons in the heat pulses is smallest in the direct-gap semiconductor GaAs, where rapid recombination depletes the populations of electrons and holes in just a few nanoseconds. More noticeable low frequency phonon components are seen in heat pulses in the indirect-gap semiconductors Ge and Si. At sufficiently high excitation densities (∼60 W/mm2) in Ge, there is a suppression of the low-frequency phonon signal, which may result from phonon absorption within a cloud of electron hole droplets. An interesting alternative hypothesis is that the acoustic phonons created in the plasm
Editeur
American Physical Society
Identifiant
ISSN : 1098-0121
Source
Physical review B. Condensed matter and materials physics A. 2002, vol. 65, n° 19, pp. 195205.1-195205.7
Langue
Anglais
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