Thin, coherently strained films of SiGe were deposited on Si(001) to form f
aceted, dislocation-free, three-dimensional (3D) islands via the Stranski-K
rastanov (SK) growth mode. Deposition was interrupted to determine the satu
ration 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 over
grown at various temperatures. The temperature dependence of the island num
ber 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-isl
and number density on growth rate cannot be understood without modifying th
e 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 t
he island number density is proportional to the inverse square of the Ge mo
le fraction in the alloy plus a constant. Finally, cross-sectional transmis
sion electron microscopy reveals that the island shape changes dramatically
during encapsulation, but the morphology can be kinetically preserved. (C)
1999 American Vacuum Society. [S0734-2101(99)09204-0].