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Influence of doping profiles on coherent acoustic phonon detection and generation in semiconductors

Einfluss von Dotierprofilen auf die Detektion und Generation von kohärenten akustischen Phononen
: Hudert, F.; Bartels, A.; Dekorsky, T.; Köhler, K.


Journal of applied physics 104 (2008), No.12, Art. 123509, 5 pp.
ISSN: 0021-8979
ISSN: 1089-7550
Journal Article
Fraunhofer IAF ()
III-V semiconductor; III-V Halbleiter; time resolved spectroscopy; zeitaufgelöste Spektroskopie; optical spectroscopy; optische Spektroskopie

The doping profile in different n-doped GaAs homoepitaxial structures grown by molecular beam epitaxy is investigated in the time domain by employing a laser based picosecond ultrasound technique in a contactless and noninvasive way. Experiments based on asynchronous optical sampling employ two femtosecond lasers, which allow us to detect changes in the optical reflectivity over a 1 ns time delay with a signal-to-noise ratio of 10(exp 7) and 100 fs time resolution in <1 min of acquisition time. We show that the doping profile with doping densities of the order of 10(exp 18) cm-3 can be detected with picosecond ultrasound, although there is no difference in the acoustic properties of the doped and undoped region. The detection mechanism is based on a different sensitivity function for a coherent strain pulse in the doped and undoped regions. These results are corroborated by experiments at room temperature and 10 K.