Modulierte zweidimensionale Elektronengase und Spin-Bahn Wechselwirkung in InAs und GaAs Heterostrukturen (English shop)

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This thesis investigates the electronic transport properties of InAs/InGaAs and GaAs/AlGaAs heterostructures at low temperatures (0.1 K < T < 4.2 K) and in magnetic fields (B < 7 T). In the InAs/InGaAs structures, a two-dimensional electron gas is located in a pseudomorphically strained InAs channel. These heterostructures are grown by molecular beam epitaxy on GaAs substrates. Owing to the lattice mismatch between InAs and GaAs, these structures exhibit a characteristic cross-hatch pattern, which is marked by an undulation of the heterostructure surface. It is shown that the transport properties of the electron gases display clear signatures of an electrostatic modulation. The origin of this modulation is attributed to spatially fluctuating strain potentials that arise from the lattice-mismatched epitaxial crystal growth. In addition to this electrostatic modulation, measurements of the transport properties in tilted magnetic fields show that the electron gases are also subject to a spatial modulation associated with the undulation of the cross-hatch pattern. To investigate the mesoscopic transport properties of the electron gases in these InAs/InGaAs heterostructures, measurements on open quantum dots are carried out. From the conductance fluctuations of these systems, the phase coherence length of the electrons can be determined at T < 1 K. In very narrow electron channels of various widths, the influence of spin-orbit interaction on the magnetotransport is studied in the form of antilocalization. For a better understanding of the dependence of antilocalization on the width of the electron channels, measurements on a GaAs/AlGaAs heterostructure are performed. Here, a hitherto unexplained behaviour of the signatures of spin-orbit coupling in magnetotransport as a function of channel width is observed.