X-ray characterization of self-organized periodic body-centered tetragonal lattices of SiGe dots

Modern nanotechnology offers new possibilities to create artificial materials such as three-dimensional (3D) ordered island crystals that might be of interest e.g., for optoelectronic applications. We demonstrate that a completely self-organized body-centered tetragonal lattice of SiGe dots can be achieved by reduced pressure chemical vapor deposition (RPCVD). Main subject of this paper is the application of different X-ray diffraction techniques to study the structural properties of a large ensemble of buried SiGe dots with the target to optimize deposition conditions. This includes specular ω-2Θ scans to reveal vertical periodicity and strain state, reciprocal space mapping to determine lateral arrangement and symmetry of dots, and in-plane diffraction to get better inside to the lateral strain distribution close to the surface for further growth simulations. SEM cross-section images of a SiGe/Si superlattice of imperfect lateral periodic structure of SiGe dots.