We present a structural analysis of Ge islands on Si(100) substrates using grazing incidence small angle X-ray scattering (GISAXS). GISAXS is a nondestructive and powerful technique for structural characterization of islands fabricated on a substrate. From the GISAXS pattern it is possible to determine the size, the shape, the inter-island distance and the size distribution of islands. In this work, the samples were prepared with high-vacuum evaporation of a 10 nm thick Ge layer on Si(100) substrate heated at 200 degrees C. The samples were annealed at 500-700 degrees C for 1 h in vacuum, yielding to island formation. The implementation of such Ge islands into silicon solar cells is proposed. (c) 2005 Elsevier B.V. All rights reserved.