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2008
Journal Article
Titel
Influence of doping profiles on coherent acoustic phonon detection and generation in semiconductors
Alternative
Einfluss von Dotierprofilen auf die Detektion und Generation von kohärenten akustischen Phononen
Abstract
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.
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