Mechanisms determining three-dimensional SiGe island density on Si(001)

Thin, coherently strained, films of SiGe were deposited on Si(001) in the S transki-Krastanow (SK) growth mode to form small, faceted, dislocation-free -three-dimensional (3D) islands. The number density of these islands was de termined as functions of SiGe alloy composition, growth rate, and substrate temperature during growth. From these experiments, the classical model of 3D island nucleation and growth yields an approximate activation energy for diffusion of Ge dimers on a Ge covered Si(001) surface of 0.70 eV. The dep endence of the 3D-island number density on growth rate cannot be understood without modifying the classical model to account for the wetting layer pre sent in SK systems. Heteroepitaxial strain is not included in the classical model of island nucleation and growth. A simple linear elastic model that fits the data is developed that predicts the island number density is propo rtional to the inverse square of the Ge mole fraction in the alloy plus a c onstant.