Transport phenomena in quantum wells and wires in presence of disorder and interactions

Abstract: Present-day electronics employ circuits of smaller and smaller dimensions, and today the length scales are so small that the laws of physics which rule micro-cosmos, quantum mechanics, become directly important. This thesis reports on theoretical work on electron transport in different nanostructures. We have studied semiconductor quantum wells, layered materials where each layer can be only a few atomic layers thick, and transport in thin atomic wires. The layered materials have been studied semi-classically by means the so-called Bolzmann equation and Monte-Carlo techniques. The works on layered materials focused on effects of resonant scattering mechanisms on the electron transport and the feasibility to use semiconductor super- lattices for generating terahertz (THz)radiation. The quantum wires were modeled by 1D Hubbard chains connected to semi-infinite leads and were treated fully quantum-mechanically via the time-dependent density- functional theory (TDDFT). Our TDDFT treatment appears to be able to capture complex features due to competition between correlation and disorder. The merits of the coherent-potential approximation are also analyzed for contacted chains. In total, four papers are included in the thesis. In paper I, Monte Carlo simulations of transport in various two- dimensional semiconductor hetero-structures, in particular in cases where accurately calculated scattering probabilities are needed. In paper II, we present result for electron transport in į-doped Si/SiGe quantum wells at different temperatures and field strengths. In paper III, we develop a Monte-Carlo technique to handle electron transport between quantum-well layers when an electric field is applied along the growth direction. We use this method to study scattering- assisted transport under strong fields in the Wannier-Stark regime. In paper IV, finally, the static and dynamical behavior of 1D Hubbard chains are investigated. The focus is on how the interplay of interactions and disorder affects the localization of fermions in Hubbard chains contacted to semi-infinite leads.