Strain characterization of Ge1−xSix and heavily B-doped Ge layers on Ge(001) by two-dimensional reciprocal space mapping

Abstract

Two-dimensional (2D) reciprocal space mapping of high-resolution X-ray diffraction has been used to characterize the strain in structures with Ge1−xSix and heavily B-doped Ge layers grown by molecular beam epitaxy on Ge (001). Tetragonal lattice distortion yielding strain along and perpendicular to the surface has been determined for Si fractions from 10 to 40% and B concentrations in the range from 6 × 1019 to 8 × 1020cm−3. A sensitive estimate of the critical thickness for Ge1−xSix layers grown on Ge has been obtained by analyzing 2D-reciprocal space maps around the (113) reflection. The lattice contraction coefficient due to B doping in Ge was β = 4.3 × 10−24cm3 per B atom. For CB ≥ 2.2 × 1020cm−3, B precipitation in the form of epitaxial interfacial layers on (001) and (113) planes in the Ge was observed by cross-sectional transmission electron microscopy. Electrical characterization of the samples showed that doping concentrations ≤ 2 × 1020cm−3 could be fully activated.