X-Ray Standing Wave and High Resolution Diffraction Study of Si/Ge Superlattices

Abstract

ABSTRACTIn modern technology more and more attention is given to epitaxial superlattices. III/V, and more recently Si/Ge superlattices are widely studied because of their applications in integrated optoelectronics. Since the physical properties are strongly dependent on structural characteristics, it is evident that accurate characterization methods are required in order to improve their quality and obtain optimal behavior. X-ray high resolution diffraction is extensively and successfully used to this purpose. In general diffracted intensity is measured close to strong substrate reflections where satellite peaks from superlattice take place. If the crystalline quality, mainly concerning thickness layer uniformity and interface abruptness is good, several orders of diffraction from the superlattice are visible, and fitting based on kinematical or dynamical diffraction can provide information about many structural parameters of the superlattice. However from diffracted intensity the information about the phase of the structure factor is lost. It is well known that the X-ray Standing Wave (XSW) technique can provide direct information about the phase [1]. In this paper we present measurements and calculations relative to the extension of the XSW method to the study of MBE-grown Si/Ge superlattices. The novelty consists in using the superlattice satellite peaks close to a strong reflection from the substrate to form the standing wave field which in turn excites the atoms whose fluorescence is measured. These satellite peaks correspond to high-order diffraction for the superlattice periodicity.