<title>Observation of bulk-like LO phonons in GaAs/Al<formula><inf><roman>x</roman></inf></formula>Ga<formula><inf><roman>1-x</roman></inf></formula>As superlattices and quantum wells</title>

Abstract

Picosecond pulses are used to measure the hot phonon generation rate ((partial)Nq/(partial)t) of Raman active GaAs LO phonons in several GaAs/AlxGa1-xAs superlattices (SL's) and quantum wells (QW's). Drastic increase in (partial)Nq/(partial)t is observed as the barrier width (Lb) decreased below a critical value for SL's with x >= 0.4. This is interpreted as due to a phonon transition from confinement to propagation. In contrast, for x <EQ 0.2 we do not observe this LO phonon transition. In this case the LO phonons only show a bulklike character regardless of the Lb's considered. We have also observed the existence of a critical x equals x0 below which the LO phonons are no longer confined. Estimate of the LO phonon penetration depth into the barriers are also obtained for the different x values.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.