  Molecular beam epitaxy of Ge (111) thin films on epitaxial-Gd2O3/Si(111)
substrates is reported, along with a systematic investigation of the evolution
of Ge growth, and structural defects in the grown epilayer. While Ge growth
begins in the Volmer-Weber growth mode, the resultant islands coalesce within
the first 10 nm of growth, beyond which a smooth two-dimensional surface
evolves. Coalescence of the initially formed islands results in formation of
rotation and reflection microtwins, which constitute a volume fraction of less
than 1 %. It is also observed that while the stacking sequence of the (111)
planes in the Ge epilayer is similar to that of the Si substrate, the (111)
planes of the Gd2O3 epilayer are rotated by 180 degree about the [111]
direction. In metal-semiconductor-metal schottky photodiodes fabricated with
these all-epitaxial Ge-on-insulator (GeOI) samples, significant suppression of
dark current is observed due to the presence of the Gd2O3 epilayer. These
results are promising for application of these GeOI structures as virtual
substrates, or for realization of high-speed group-IV photonic components.
