Continuous formation and faceting of SiGe islands on Si(100)

Abstract

The multiscale mechanisms leading to the formation of faceted quantum dot (QD) islands during Si1−xGex/Si(100) heteroepitaxy were studied by scanning tunneling microscopy. The entire evolution from an initial morphological instability of the strained alloy to final {105} faceted pyramidal QD islands is continuous. Shallow mounds, generated by the alloy instability, are bounded by alternating (100) terraces and single-layer steps. Growth of the mounds in height without lateral expansion drives a continuous increase in mound slope and step density up to a critical angle of about 6°. Kinetic constraints then force the nucleation of small {105} protofacets, which expand and ultimately coalesce to form the {105} facets bounding pyramidal QD islands.