Short-period SinGem strained-layer superlattices grown from gas sources by synchrotron-radiation-excited chemical-beam epitaxy

Abstract

Short-period SinGem strained-layer superlattices were successfully grown on Si (100) substrate from gas sources by synchrotron-radiation-excited chemical-beam epitaxy at 250 °C. Atomically sharp interfaces between the Si and Ge layers and two-dimensional morphology were obtained. With thinner Ge layers, the misfit strain is relieved by atomic-scale roughness at the interfaces; as the Ge layers become thicker, misfit dislocations become the main relief mechanism. The thickness of Si and Ge layers as derived from spectroscopic ellipsometry agreed nicely with images of the lattices. The dielectric constants of the growing Si and Ge top layers were much lower than those of Si and Ge bulk crystals, which is consistent with the mechanism of photoepitaxy, that is, the formation of a hydrogenated network as the precursor state followed by photolytic crystallization.