High resolution X-ray diffraction studies of semiconductor superlattices

Abstract

Recent years have seen the development and application of high resolution X-ray diffraction techniques in order to non-destructively assess the structural and compositional quality of complex epitaxial semiconductor structures. The most widely used technique is double crystal diffraction, which is used to record the complex multipeaked rocking curves associated with current multilayer epitaxial structures. However, effects of material quality on this diffraction data can only be quantified and understood by the application of a versatile theoretical rocking curve simulation package which is capable of simulating the effects of small deviations from the ideal material structure. The use of both theory and experiment to identify and solve growth induced materials problems in semiconductor superlattice structures is demonstrated with a number of examples. In Si 1- x Ge x /Si superlattices grown by molecular beam epitaxy a detailed analysis of the asymmetric broadening of superlattice reflections enables this effect to be directly attributed to a slight drift of 1.25% in the Ge flux during the growth run. In In 1- x Ga x As/InP superlattices grown by MOCVD the exact nature of the growth system improvements necessary to sharpen the layer interfaces are identified and in MBE grown InSb/CdTe superlattices the presence and nature of thin, highly strained interfacial layers is assessed. The limitations of the double crystal system are outlined along with the advantages of moving towards a multiple crystal diffraction system.