HOT-PHONON GENERATION IN GAAS/ALXGA1-XAS SUPERLATTICES - OBSERVATIONS AND IMPLICATIONS ON THE COHERENCE LENGTH OF LO PHONONS

Abstract

Using picosecond Raman scattering, hot-phonon occupation numbers (N) of GaAs and GaAs-like LO phonons have been studied over a wide range of structural parameters in more than 30 GaAs/AlxGa1−x As superlattices. In addition, simultaneous measurements of these LO phonon modes in bulk GaAs and AlxGa1−x As alloys are made for comparison. N values of both GaAs and GaAs-like modes of the superlattices are comparable to or larger than those of bulk GaAs or AlxGa1−x As alloys for x<0.2. On the other hand, N values of GaAs or GaAs-like LO phonons are much smaller for x>0.35, unless the barrier widths are very thin (<15 Å). The implications of our results on spatial properties of LO phonons are discussed and compared with relevant theoretical and experimental studies.