Schmalzbauer, M: Heterostructure design of Si/SiGe

2D-confined carrier systems have given access to the exploration of manifold quantum effects in fundamental research and also led to numerous device concepts for commercial electronic applications. Additionally, the possibility to control the 2D carrier density via gate voltages through the electric field-effect offers a great advantage of external manipulation of the system. With the optimization of lithography on a nanometre scale, gated 2D systems in semiconductor heterostructures are currently intensively studied as platforms for few to single-carrier devices. In this context, a precise control of the heterostructure layout including the doping, as well as an understanding of charge reconfiguration effects within the device, are important challenges. This thesis, addresses the heterostructure optimization and focuses on a precise field-effect control of Schottky top-gated modulation doped Si/SiGe heterostructures. For the optimization of the heterostructure design, several parameters which affect the strain, the band offset and the doping degree in Si/SiGe two-dimensional electron systems are precisely studied. In parallel, the field-effect influence on Si/SiGe heterostructures is used to identify the origin of disorder and possible sources of charge noise. In this connection, finally a modified charge transfer model including a polarizability of neutral phosphorous atoms inside the doping layer is developed.