Structural investigations of the α₁₂Si–Ge superstructure

Abstract

This article reports the X-ray diffraction-based structural characterization of the α12multilayer structure SiGe2Si2Ge2SiGe12[d'Avezac, Luo, Chanier & Zunger (2012).Phys. Rev. Lett.108, 027401], which is predicted to form a direct bandgap material. In particular, structural parameters of the superlattice such as thickness and composition as well as interface properties, are obtained. Moreover, it is found that Ge subsequently segregates into layers. These findings are used as input parameters for band structure calculations. It is shown that the direct bandgap properties depend very sensitively on deviations from the nominal structure, and only almost perfect structures can actually yield a direct bandgap. Photoluminescence emission possibly stemming from the superlattice structure is observed.

Determination of the superlattice structure factor by X-ray diffraction using a temperature gradient

“…In this case, X-ray nondestructive control of SL parameters is of great importance. Studies of SL by various X-ray methods have been carried out by Afanas'ev et al (1998), Engstro ¨m et al (1999, Holy et al (2001), Roch et al (2001), Etzelstorfer et al (2015). Vardanyan et al (1985a,b) developed a dynamical theory of X-ray diffraction by the one-dimensional ideal SL of an arbitrary model, and they obtained formulas for structure factors for various SL models.…”