Study of strain and composition of the self-organized GE dots by grazing incident X-ray diffraction

Grazing incident X-ray diffraction at different grazing angles for self-organized Ge dots grown on Si(0 0 1) are carried out and lattice constant expansions of 1.2% parallel to the surface as compared with the Si lattice are found within the Ge dots. A 3.1% lattice expansion of the Ge dots along the growth direction is also found by ordinary X-ray (0 0 4) diffraction. According to the Poisson equation and the Vegard law, our results infer that the Ge dot should be a partially strain relaxed SiGe alloy with Ge content of about 55%.