Molecular beam epitaxy and defect structure of Ge (111)/epi-Gd2O3 (111)/Si (111) heterostructures.

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 the 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° 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 applications of these GeOI structures as virtual substrates or for realization of high-speed group-IV photonic components. [ABSTRACT FROM AUTHOR]