Using gradient corrected periodic density functional theory calculations, we have investigated the structure, energetics, bonding, and diffusion of Ge in bulk alpha-quartz and amorphous a-SiO2 matrices as well as at the Si(001)/a-SiO2 interface. Our calculations show that Ge atoms undergo migration in a-SiO2 with a moderate barrier (<2.5 eV) and prefer to remain in the Si part near the Si(001)/a-SiO2 interface via site exchange reaction with Si lattice atoms, while the kicked-out Si atoms are preferentially incorporated into the a-SiO2 matrix. We also discuss implications of the Ge-Si exchange process for Ge nanoparticle formation in an oxide matrix. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.2978960] All rights reserved.