Properties of Si1−xGex three-dimensional islands

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Abstract
Thin, coherently strained films of SiGe were deposited on Si(001) to form faceted, dislocation-free, three-dimensional (3D) islands via the Stranski–Krastanov (SK) growth mode. Deposition was interrupted to determine the saturation island number density as a function of alloy composition, substrate temperature during growth, and growth rate. To control the shape of buried islands during encapsulation with Si, the 3D islands were embedded and overgrown at various temperatures. The temperature dependence of the island number density yields an approximate activation energy of 0.7 eV for diffusion of Ge dimers on a Ge covered Si(001) surface. The dependence of the 3D-island number density on growth rate cannot be understood without modifying the classical model of nucleation and growth to account for the wetting layer present in SK systems. To explain the island number density as a function of alloy composition, a simple linear elastic model is developed in which the island number density is proportional to the inverse square of the Ge mole fraction in the alloy plus a constant. Finally, cross-sectional transmission electron microscopy reveals that the island shape changes dramatically during encapsulation, but the morphology can be kinetically preserved.