Phase spectroscopy in semiconductor structures

Summary form only given. We present applications of phase/amplitude spectroscopy in GaAs-based semiconductor structures, using Fourier Transform Spectral Interferometry. This technique allows one to measure both phase and amplitude of an optical pulse transmitted by the sample and therefore provides simultaneous absorption and refractive index measurement. We have used this approach to study how the optical response is affected by quantum confinement, temperature and external perturbations (e.g., magnetic field, optical excitation). We show here two studies of particular interest. First, the study of the dielectric function of a GaAs/AlGaAs multiple quantum well structure (MQWS) near the bandgap and at different temperatures. We show that it is possible to describe the complex dielectric function across the exciton resonances by analytical formulae assuming that the MQWS has a fractional dimension that translates the fact that real QWs are structures intermediate between the 3D unconfined bulk and ideal 2D systems. Second, the study of magnetically induced Fano-resonances (FR) in bulk GaAs under various excitation densities. They originate from a quantum interference between degenerate 1D continua and magnetoexcitons of different Landau levels coupled via Coulomb interaction. Using new analytical expressions describing this interference, we determine for the first time the collisional broadening of the continuum states.