Quantitative analysis of strain relaxation and mosaicity in short period Si mGe n superlattices using reciprocal space mapping by X-ray diffraction

Abstract

Double crystal and triple axis X-ray diffractometry was used to characterize in detail the structural properties of several short period Si 9Ge 6 and Si 6Ge 4 superlattices grown by molecular beam epitaxy on thick step-graded SiGe alloy buffers resulting in reduced dislocation densities. Precise strain data were extracted from 2-dimensional reciprocal space maps around (004) and (224) reciprocal lattice points. Due to the much higher instrumental resolution of triple axis diffractometry Bragg reflection peaks from buffers and superlattices, which often overlap in such almost free-standing superlattices, have been clearly separated experimentally, and minute changes in strain status and mean Ge content are determined. From the distribution of diffusely scattered intensity around reciprocal lattice points the correlation function of the deformation field due to structural defects has been calculated using a model based on the kinematical theory of X-ray diffraction and on a formalism well known from statistical optics.