In this article, we demonstrate the influence of substrate temperature during migration-enhanced epitaxy (MEE) process of GaAs epitaxy on a vicinal surface of Ge (100), 6 degrees offcut towards the (111) plane. It was found that the offcut surface is not the sufficient condition for suppressing the formation of antiphase domains at the GaAs/Ge interface. Rather, it has to be complemented by low substrate temperature during the MEE process. GaAs grown at 250 degrees C, the lowest temperature among all the samples, exhibits the smoothest surface and best structural and optical qualities, as characterized by atomic force microscopy, cross-sectional transmission electron microscopy, and low-temperature photoluminescence, respectively. At this substrate temperature, As dimers are adsorbed onto the substrate surface more readily with negligible reevaporation, ensuring complete coverage on the Ge surface with double-atomic steps. Complete coverage by As proved to be crucial in preventing the occurrence of inversion boundaries, or at the very least ensure fewer As vacancies that may act as defect centers. Furthermore, low substrate temperature shortens the migration distance of Ga adatoms, minimizing their adsorption into the kinks and step edges, resulting in two-dimensional growth mode instead of step-flow growth mode. (c) 2006 American Vacuum Society.