Direct growth of relaxed Ge layers on Si(001) substrates was achieved using Sb as a surfactant. Deposition of Ge at substrate temperatures around 670 degrees C under large Sb flux resulted in complete compensation of lattice mismatch via a regular array of 90 degrees dislocations at the interface. A residual 0.20% tensile strain is found caused by thermal mismatch between Ge and Si. The density of defects threading through the Ge films is as low as 5 x 10(7) cm(-2). This is ascribed to an abrupt strain release during the initial micro-rough growth phase, which occurs only under the selected growth conditions. We also observed n-type Sb background doping levels in the Ge layers well below 10(17) cm(-3) presumably related to an enhanced Sb surface segregation due to the high growth temperature. Such relaxed Ge films grown by surfactant-mediated epitaxy on Si(001) open attractive perspectives for integration of novel Ge devices into mainstream Si technology. (c) 2005 Elsevier B.V. All rights reserved.