Charge transport in semiconductor nanostructures investigated by time-resolved multi-terahertz spectroscopy

Terahertz conductivity spectra contain information on charge transport mechanisms and charge confinement on nanometer distances. In this thesis, we make a substantial progress in understanding of terahertz conductivity in several regimes. First, we theoretically investigate linear terahertz conductivity of confined electron gas: while the spectra of degenerate electron gas exhibit geometrical resonances, the response in non-degenerate case smears into a single broad resonance due to the wide distribution of charge velocities. Then, we theoretically and experimentally analyze various TiO2 nanotube layers: their linear charge transport properties strongly depend on the fabrication process, which influences the internal structure of the nanotube walls. In the main part of the thesis, we develop a framework for evaluation of the nonlinear terahertz response of semiconductor nanostructures based on microscopic Monte-Carlo calculations. The nonlinear regime is highly non-perturbative even in moderate fields as illustrated by efficient high harmonics generation. We investigate measurable nonlinear signals for various semiconductor nanostructures; metallic nanoslits filled with nanoelements are the most promising for the experimental observation of terahertz nonlinearities. These nonlinearities per unit charge are..