Raman scattering and optical spectroscopy of nonperiodic gallium arsenide/aluminum arsenide superlattices.

摘要

This thesis presents results of Raman scattering and optical measurements in nonperiodic GaAs/AlAs superlattices based on Fibonacci, random, and Thue-Morse sequence. In addition, numerical models of these systems are used to discuss the experimental results.;The Raman spectra in the acoustic phonon region show differing behavior depending on whether the incident light is in resonance with particular electronic states or not. The off-resonance spectra can be explained using a simple photoelastic model, while the resonant spectra resemble weighted phonon density of states. The latter is explained by a model based on the phenomenon of acoustic phonon surface avoidance and the existence of surface electronic excitations.;Optical measurements, reflectivity and transmission, were also performed. The absorption coefficient is compared to a joint density of states calculation based on an effective mass model. Peaks in the absorption coefficient are assigned to excitons.