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 s uperlattices. In addition, simultaneous measurements of these LO phono n 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 com paring Stokes and anti-Stokes intensities after appropriate correction s for small resonant Raman effects in each sample, are comparable to o r 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 su ggest that both GaAs and GaAs-like LO phonons observed in Raman scatte ring are spatially extended for x less-than-or-equal-to 0.2, while the y are confined within individual wells for x>0.3.