Germanium and germanium rich silicon germanium are of interest as channel materials for extremely scaled CMOS. Although PMOS performance is good the characteristics of germanium NMOS transistors are inadequate because the necessary high level of donor activation cannot be achieved in shallow junctions. In this work we describe a study of the activation and deactivation of donors in germanium using shallow phosphorous implants into p-type Ge and Ge or Si implants into Ge uniformly doped with Sb. The techniques of secondary ion mass spectrometry (SIMS), spreading resistance, DLTS and positron annihilation have been used to study the activation and defects evolution during various anneal stages. It is postulated that the primary reasons for low activation of donors are reactions with vacancies. These proceed as V-D which is thought to be mobile at the anneal temperature reacting with more donors to produce complexes of the form V-D(n) or possibly V(2)-D(n) which are acceptor like. (C) 2008 Elsevier B.V. All rights reserved.