Low pressure chemical vapor deposition (LPCVD) of germanium crystallites on silicon surfaces from a digermane precursor has been studied in situ and in real time by spectroscopic ellipsometry (SE) in the range 1.2-4.7 eV and ex situ by scanning force microscopy (SFM). As substrates, hydrogen-terminated silicon surfaces were employed. A two-layer model consisting of a pure germanium layer and a layer of germanium islands, was used to simulate the ellipsometric data. To treat the wetting and island layer a Bruggemann effective medium approximation (EMA) of germanium and voids was used. The time evolution of the wetting layer and the island layer, could be described independently by the model, resulting in separate growth rates for each layer. The onset and end of nucleation could be determined with high-time resolution. To our knowledge, this is the first report on the evaluation of real-time ellipsometric data to model Stranski-Kyastanow (SK) growth of germanium on a silicon surface. Measurements of the topography by SFM showed a smooth surface between germanium islands at the end of the deposition process. The amount of Ge contained in the islands is in good agreement with a theoretical growth model. (C) 2002 Elsevier Science B.V. All rights reserved.