Symmetrically strained SiGe/Ge multilayers were grown epitaxially on Si(001) by low-energy plasma-enhanced  chemical  vapour deposition  LEPECVD. Using exceptionally high growth rates around 5 nm/s and low substrate temperatures of the order of 500^o C, structures containing up to 1000 SiGe/Ge double layers with a thickness of 50 nm each could be realized [1]. HRXRD methods are used to evaluate lattice strain and relaxation, lattice tilt, layer thickness, composition and dislocation densities. Single scan simulations on symmetric (004) and asymmetric (115) reflections are performed in order to obtain precise information about the Multi Quantum Wells (MQW) system. The crystalline perfection can be determined with highest precision using the reflections from the Si substrate as internal reference.

The figure 1 shows an example of a Reciprocal Space Map (RSM) in the vicinity of the Si(004) reflection, where the two main maxima correspond to diffraction from the SiGe and Ge layers, respectively, and where the superlattice reflections are clearly resolved. In addition, diffused scattering occurring around the SiGe layer diffraction peak shows the presence of defects in the MWQ. A reasonable fit of the corresponding rocking curve is only possible for such a structure if the defects are taken into account.

Fig. 1 RSM of (004) in a MQW

1. H. von Känel, M. Bollani, M. Bonfanti, D. Chrastina, D. Colombo, A. Dommann, M. Guzzi, G. Isella, A. Miranda, E. Müller, A. Neels, J. Osmond, B. Rössner, R. Sordan, F. Traversi, Epitaxial Si-Ge Heterostructures and Nanostructures for Optical and Electrical Applications, Proceedings of the 2nd Conference on Nanostructures (NS2008), 2008, Iran.

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