Transition metal doping in Ge

We present ab initio electronic structure calculations within density functional theory of the structural, electronic and magnetic properties of transition metal impurities into a Ge matrix. We examine the case of dopant clusters, made of up to three transition metal impurity atoms in substitutional and/or interstitial sites, embedded in the Ge matrix. We find that while isolated interstitial TM impurities are energetically unfavored over the substitutional sites, they can be stabilized thanks to the interaction with substitutional sites nearby. Mn impurities show a tendency to cluster and exhibit magnetic alignment strongly dependent on the occupied sites. The electronic properties of the most stable configurations are analyzed and discussed. (c) 2006 Elsevier B.V. All rights reserved.