Inverted Ge islands in {111} faceted Si pits—a novel approach towards SiGe islands with higher aspect ratio

Details Inverted Ge islands in {111} faceted Si pits—a novel approach towards SiGe islands with higher aspect ratio Inverted Ge islands in {111} faceted Si pits—a novel approach towards SiGe islands with higher aspect ratio

Jun 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010njph...12f3002g&link_type=abstract

New Journal of Physics, Volume 12, Issue 6, pp. 063002 (2010).

Physics

10

Scientific paper

A detailed study of the so far unexplored Ge island nucleation on Si (001) substrates patterned with {111} faceted pyramidal pits is reported. The pits are defined by an anisotropic wet-chemical etch through a SiNx hard mask. Due to the self-limiting of the wet etch, an extremely uniform pit pattern is achieved. On these substrates, Ge layers were grown by solid source molecular beam epitaxy at various growth temperatures TGe. For TGe=550 °C, Ge fills the pits in the form of inverted {111} pyramids with a rounded apex and a (001)-oriented top surface. These islands have aspect ratios much larger than upright pyramids and domes that are usually obtained on substrates with cylindrical pits fabricated by lithographic techniques and reactive ion etching. Based on the experimentally determined shape, three-dimensional (3D) energy level calculations in an envelop function approach have been performed for the inverted pyramids. They show that, due to the orientation of the pyramid square base along lang110rang directions, the overlap between the hole ground states and electron states confined to the Si conduction band valleys perpendicular to the growth direction is much larger than for upright SiGe domes and {105} pyramids. For elevated growth temperatures around 700 °C, already a Ge coverage of five monolayers induces a strong Si transfer into the {111} pits, effectively converting them towards {1 1 10} faceted ones.

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