Quantum electronic transport in low-dimensional semiconductors

Abstract: Electronic transport is studied at low temperatures in two-dimensional electron gases (2DEGs) and in mesoscopic semiconductor microstructures. The method of microwave-detection of the Shubnikov-de Haas effect for the contact-free characterisation of transport properties of 2DEGs is explored using both magnetic-field modulation and light-induced carrier modulation. The methods are compared to magneto-photoluminescence (PL), cyclotron resonance (CR), optically detected CR, and to standard electrical measurements. The effect of plasma dry etching of the surface of high-mobility 2DEG samples on the properties of the 2DEG is studied. The PL- and the transport properties of the 2DEG and the concentration of a paramagnetic surface defect created by the etching are found not to be correlated to each other. The classical and the quantum mechanical dynamics of electrons in mesoscopic, open, triangular electron billiards is studied. The temperature-averaged magnetoresistance can, using simulations, be explained by specific, classical electron trajectories, the relative importance of which is shown to depend on their Lyapunov stability. Quantum mechanical calculations reproduce observed conductance fluctuations which can be related to a specific electron orbit. Visualizations of the classical and the quantum mechanical electron density distribution inside the billiard are compared at various magnetic fields The resistance of quasi-ballistic wires and of ballistic electron cavities is studied in the non-linear transport regime. The energy dependence of the phase-breaking rate of non-equilibrium electrons in these structures is determined from the line shape of the suppression of weak localization due to voltage induced electron-electron interaction. The two terminal resistance of electron billiards without symmetry axis perpendicular to the current direction is found to be not symmetric upon current reversal in zero magnetic field. This effect appears to be related to ballistic weak localization inside the billiard.