InSb epilayers and InSb/Al0.20In0.80Sb quantum well structures were grown on Ge(001) substrates by molecular beam epitaxy. Epilayers grown using a two-step process, which involved different temperatures, were characterized in situ using reflection high energy electron diffraction and studied ex situ using high-resolution x-ray diffraction, Nomarski optical microscopy, and Hall-effect measurements. The narrowest x-ray rocking curve width for 2.0- and 5.0-mu m-thick InSb epilayers were 250 and 173 arc sec, respectively. Electron mobilities in the 5.0-mu m-thick InSb epilayer and the InSb/Al0.20In0.80Sb single quantum well at room temperature were 34 500 and 8600 cm(2)/V s, respectively, which are the highest values for these films on Ge(001) substrates reported to date.