CONFINED-TO-PROPAGATING TRANSITION OF LO PHONONS IN GAAS/ALXGA1-XAS SUPERLATTICES OBSERVED BY PICOSECOND RAMAN-SCATTERING

Abstract

We report the first observation of a confined-to-propagating transition of LO phonons in GaAs/AlxGa1-xAs superlattices (SL's). Our samples are two series of SL's with constant GaAs layer widths (L(z)) and x, while the AlxGa1-xAs layer widths (L(b)'s) varied. Using picosecond Raman scattering, we have observed a sudden increase in the generation rate of the Raman-active hot phonons as L(b) decreased over a narrow range for both series of samples. We demonstrate that this abrupt increase is due to the sharp transition from the so-called confined to the propagating LO phonons. From our results we have determined the GaAs LO phonon penetration depth into the AlxGa1-xAs layers.