Residual strain in Ge pyramids on Si(111) investigated by x-ray crystal truncation rod scattering

Epitaxial growth of germanium on boron-terminated Si(111) results in the formation of triangular pyramidal Ge islands which are partially relaxed. We show that the termination of the Si(111) surface with 1/3 ML of boron is essential for the formation of faceted islands. We have investigated the residual strain in the Ge islands using x-ray crystal truncation rod scattering, and developed an analytical expression for the scattered intensity from islands with a nonuniform lattice parameter. We compare the measured intensity to x-ray scattering profiles calculated on the basis of different strain models. It is found that the Ge lateral lattice parameter changes linearly from the bottom to the top of the islands.