The molecular beam epitaxial growth of InAsSb on GaAs-coated patterned Si substrates is reported. The epilayers are grown embedded in wells so a coplanar Si-InAsSb surface can be obtained. The InAsSb epilayer morphology is compared for different substrate conditions (Si-well, Si-mesa, GaAs) using Nomarski contrast microscopy. High-voltage electron microscopy shows that the threading defect density of the InAsSb layers is high but decreases with thickness. In the reduced area electron diffraction pattern of the GaAs-InAsSb interface, additional diffraction spots are visible due to microtwins in the InAsSb. High-resolution electron microscopy reveals a regular array of misfit dislocations relieving the 14.2% lattice mismatch in the early stage of growth. Stripping Hall measurements for InAs0.05Sb0.95 show a constant mobility as a function of depth for the top 2-mu-m of the film and the 300 and 77 K mobility values are comparable.