In0.01Ga0.99As thin films free of anti-phase domains were grown on 7 degrees offcut Si (001) substrates using Ge as buffer layers. The Ge layers were grown by ultrahigh vacuum chemical vapor deposition using low/high temperature' two-step strategy, while the In0.01Ga0.99As layers were grown by metal-organic chemical vapor deposition. The etch-pit counting, cross-section and plane-view transmission electron microscopy, room temperature photoluminescence measurements are performed to study the dependence of In0.01Ga0.99As quality on the thickness of Ge buffer. The threading dislocation density of Ge layer was found to be inversely proportional to the square root of its thickness. The threading dislocation density of In0.01Ga0.99As on 300 nm thick Ge/offcut Si was about 4 x 10(8) cm(-2). Higher quality In0.01Ga0.99As can be obtained on thicker Ge/offcut Si virtual substrate. We found that the threading dislocations acted as non-radiative recombination centers and deteriorated the luminescence of In0.01Ga0.99As remarkably. Secondary ion mass spectrometry measurement indicated as low as 10(16) cm(-3) Ge unintended doping in In0.01Ga0.99As. (C) 2012 Elsevier B.V. All rights reserved.