Single crystalline Germanium (Ge) has gained a lot of attention for
applications as new material in microelectronics, photovoltaics and for
photodetectors. The integration on the mature and predominating Silicon (Si)
technology platform is a challenging technical task, which offers many basic
scientific questions to be answered. This thesis is concerned with the
integration of a functional Ge layer on the Si platform via an engineered
oxide heterostructure, namely cubic PrO2. The oxide is incorporated to
compensate for the 4% lattice constant mismatch of Ge and Si, with its lattice
constant between the two semiconductors. An in situ reflection high energy
electron diffraction (RHEED) monitoring of the layer deposition by molecular
beam epitaxy (MBE) indicates that the initial growth mode of Ge on PrO2
follows a Volmer-Weber growth mode due to interface reactions, surface and
strain energies. By properly tuning the growth parameters of MBE a growth
recipe is developed, leading to the growth of atomically smooth single
crystalline Ge (111) layers on the Pr2O3 (111) / Si (111) support system. The
oxide is subject to a chemical reduction process during the Ge deposition,
resulting in a Pr2O3 stoichiometry. The closed layers are not achieved by a
change to van der Merwe growth, but by the adjustment of the growth kinetics,
resulting in a smoothing out of the Volmer-Weber growth. The development of
the recipe for the Ge layer growth is monitored with RHEED, ex situ x-ray
reflectivity (XRR) and x-ray diffraction (XRD) measurements as well as
scanning electron microscopy (SEM). These methods confirm the closed and
smooth Ge surface and the sharp interface with the underlying Pr2O3. The
closed layer stacks are investigated by synchrotron radiation x-ray
diffraction under bulk sensitive and surface sensitive measurement conditions.
This first study unveils a single crystalline type A / B / A stacking
configuration of the Ge (111) / Pr2O3 (111) / Si (111) heterostack system.
Driven by the results from the structural investigation a second study reveals
the main defect mechanismsat work by XRD pole-figure measurements and
reciprocal space maps (RSMs), supported by real space cross section
transmission electron microscopy (TEM) images along a stacking sensitive
direction. The defects limiting the long range order in the Ge layer are
identified as stacking twins, microtwins and stacking faults (Fig. 2). The
investigation of the thickness dependent behaviour discloses a threading
behaviour of microtwins and stacking faults while stacking twins are confined
to the interface. First results of high temperature UHV annealing experiments
show the reduction of diffuse scattering by strain fields in defective Ge is
possible, indicating a reduction of stacking faults, while microtwins as well
as stacking twins are not nfluenced by the annealings. Future defect
engineering approaches are required to improve the long range order of the
epi-Ge layer for technological applications
