We
demonstrate a novel growth technique, metal-catalyzed, lateral
epitaxial growth, to grow Ge films laterally on Si with reduced threading
dislocation densities (TDD). In contrast to traditional planar film
growth on Si, this technique starts with a small crystal nucleation
at a specific position on Si followed by Ge lateral film growth. In
plan-view and cross-sectional transmission electron microscopy micrographs,
high-density threading dislocations were found to be present in the
initial growth areas, while the lateral overgrowth areas demonstrated
substantially reduced TDD or even defect-free areas. Furthermore,
the X-ray diffraction results showed that the films were fully relaxed
and mostly pure Ge. Full relaxation and low TDD Ge films are two surprising
results given that the growth occurred at a low temperature (375 °C),
which cannot be understood with the current misfit dislocation nucleation
and glide model of film relaxation. For these reasons, we suggest
the presence of a new relaxation mechanism one in which the strain
induced by the lattice mismatch can be relaxed by extending preexisting
misfit dislocations and that lateral growth can “build in”
dislocations as it grows.