Molecular beam epitaxy of Ge (111) thin films on epitaxial-Gd 2 O 3 /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 Gd 2 O 3 epilayer are rotated by 180° 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 Gd 2 O 3 epilayer. These results are promising for application of these GeOI structures as virtual substrates, or for realization of high-speed group-IV photonic components.
The
rapidly increasing interest in nanowires (NWs) of GaN and associated
III-Nitrides for (opto-)electronic applications demands immediate
address of the technological challenges associated with NW-based device
processing. Toward this end, we demonstrate in this work an approach
to suppress the thermal decomposition of GaN NWs, which also serves
to passivate the surface states. Both of these effects are known to
be significant challenges in the development of GaN-NW-based devices.
The approach entails AlN capping of the as-grown GaN NWs, in the same
molecular beam epitaxy growth step. We show that the epitaxial AlN
crest that grows on the top facet of the NW arrests thermal decomposition,
while the AlN shell on the sidewalls (together with the crest) protects
the NW surface from the generation of oxygen-induced surface states.
This simple approach can be used for the development of GaN-NW-based
devices.
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