Spatial and dynamical properties of optical phonons in AlxGa1-xAs and GaAs/AlxGa1-xAs superlattices: Beyond the mean field approach

Spatial and dynamical properties of optical phonons in AlxGa1-xAs alloys and CaAs/AlxGa1-xAs quantum wells are studied. An isotopically disordered harmonic crystal model is developed to study spatial properties of optical phonons in AlxGa1-xAs alloys. In the GaAs/AlxGa1-xAs system, transmission of the GaAs optical phonons through an AlxGa1-xAs barrier is studied using three-dimensional lattice dynamical model. fully accounting for the random arrangement of Ga and Al atoms in the alloy barrier. In the AlxGa1-xAs alloy, a localized-to-extended transition is found as a function of x. In GaAs/AlxGa1-xAs quantum wells, the transmission coefficient of the GaAs LO phonons through the alloy barrier remains significant below x < 0.3. These results are in good qualitative agreement with the experimentally deduced coherence length of LO phonons from nonequilibrium hot phonon populations.