Spatial characteristics of GaAs, GaAs-like, and AlAs-like LO phonons in GaAs/AlxGa1−xAs superlattices: The strong x dependence

Using picosecond Raman scattering, hot phonon occupation numbers (N's) of GaAs, GaAs-like, and AlAs-like LO phonons have been studied over a wide range of structural parameters in more than 20 GaAs/AlxGa1-xAs superlattices. In addition, simultaneous measurements of these LO phonon modes in bulk GaAs and AlxGa1-xAs alloys are made for comparison. N's of both GaAs and GaAs-like mode of the superlattices, deduced by comparing Stokes and anti-Stokes intensities after appropriate corrections for small resonant Raman effects in each sample, are comparable to or larger than those of bulk GaAs or AlxGa1-xAs alloys for x less-than-or-equal-to 0.2. while they are much smaller for x>0.3. Our results suggest that both GaAs and GaAs-like LO phonons observed in Raman scattering are spatially extended for x less-than-or-equal-to 0.2, while they are confined within individual wells for x>0.3.