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

Abstract

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.