A set of samples with superlattice (SL) or multilayer structures in which the period was composed of 6 ML of Ge and a Si spacer were grown in order to study the localization of the electrons. The structural and optical properties were investigated. The growth of Ge islands was observed just for the SL The concentration of defects was drastically increased through proton irradiation with different fluences. A high radiation hardness was obtained for the Ge islands embedded in the SL. (c) 2008 Elsevier B.V. All rights reserved.