Strain relaxation of thin Ge layers grown by carbon-mediated epitaxy at 50 degrees C on Si(001) was investigated for a multi-step growth procedure. Additionally, the impact of the post-growth annealing temperature on the strain relaxation obtained for a single carbon-mediated growth step was analyzed. The degree of relaxation was monitored in situ by reflection high energy electron diffraction and ex situ by high-resolution x-ray diffraction and transmission electron microscopy. For multi-step growth, relaxation occurs mainly during the first cycle (growth and annealing). Full relaxation is already achieved after 3-4 cycles. The relaxation process during a single growth cycle can be divided into three sections: annealing up to 200 degrees C is sufficient to trigger most of the strain relaxation. After annealing up to 450 degrees C, the film lattice parameter already equals the Ge bulk value, though the layer shows a rough surface. Only an annealing step up to 650 degrees C results in a smooth surface and interface. Smooth and fully relaxed Ge films of only 26 nm thicknesses were obtained by carbon-mediated growth. (c) 2013 Elsevier B.V. All rights reserved.