Epitaxial growth of Ge on a thin SiO2 layer by ultrahigh vacuum chemical vapor deposition

In this work, the growth of germanium by ultrahigh vacuum chemical vapor deposition on a 0.6 nm thick SiO2 layer formed on Si(0 0 1) is investigated by in situ reflection high-energy electron diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Because Ge does not grow from germane on SiO2, nucleation sites were created by exposure of the surface to SiH4 at 650 °C prior to the Ge deposition, which is initiated at 600 °C. The first stage of Ge growth proceeds via the formation of dots that exhibit the same crystalline orientation as the Si substrate. They are assumed to grow from small apertures opened in the silica layer due to the reduction of SiO2 by Si. For further deposition time, {1 1 1}- and {1 1 3}-facetted Ge crystals are formed and the growth remains monocrystalline. The so-formed Ge crystals are found to be completely relaxed and contain some emerging defects, identified as stacking faults. No misfit or threading dislocations are observed. Consequently, the interface between Ge and the SiO2 layer remains perfectly sharp and free of defects. This relaxation without misfit dislocation is due to SiO2 layer which acts as a buffer layer that prevents the Si substrate from imposing its lattice parameter on the Ge crystal.