This paper reports the two-dimensional epitaxial growth of thin intrinsic Ge and in-situ doped n-Ge on GaAs substrates by atmospheric pressure chemical vapor deposition. High quality Ge growth on GaAs is activated almost instantly by an optimized pregrowth procedure. Ga autodoping is found to occur within the first Ge monolayers close to the Ge/GaAs interface. The introduction of high PH3 flows during the Ge growth yields the in-situ n-Ge growth on GaAs with an electrically activated dopant concentration of 3 x 10(19) cm(-3). Additionally, n-Ge selective growth on the source/drain areas of an n-GaAs metal oxide semiconductor structure, followed subsequently by the NiGe formation, has been demonstrated to yield an ohmic contact with a contact resistance of 0.13 Omega cm. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3528273] All rights reserved.