Epitaxial Ge layer growth of low threading dislocation density (TDD) and low surface roughness on Si (1 0 0) surface is investigated using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Thin seed Ge layer is deposited at 300 degrees C at first to form two-dimensional Ge surface followed by thick Ge growth at 550 degrees C. Root mean square of roughness (RMS) of similar to 0.45 nm is achieved. As-deposited Ge layers show high TDD of e.g. similar to 4 x 10(8) cm(-2) for a 4.7 mu m thick Ge layer thickness. The TDD is decreasing with increasing Ge thickness. By applying a postannealing process at 800 degrees C, the TDD is decreased by one order of magnitude. By introducing several cycle of annealing during the Ge growth interrupting the Ge deposition, TDD as low as similar to 7 x 10(5) cm(-2) is achieved for 4.7 mu m Ge thick layer. Surface roughness of the Ge sample with the cyclic annealing process is in the same level as without annealing process (RMS of similar to 0.44 nm). The Ge layers are tensile strained as a result of a higher thermal expansion coefficient of Ge compared to Si in the cooling process down to room temperature. Enhanced Si diffusion was observed for annealed Ge samples. Direct band-to-band luminescence of the Ge layer grown on Si is demonstrated. (C) 2011 Elsevier Ltd. All rights reserved.