Isovalent doping and the C_iO_i defect in germanium

Oxygen–carbon defects have been studied for decades in silicon but are less well established in germanium. In the present study we employ density functional theory calculations to study the structure of the C_iO_i defect in germanium. Additionally, we investigate the interaction the C_iO_i defect with isovalent dopants such as silicon and tin. It is calculated that the C_iO_i defects will preferentially form near isovalent dopants in germanium. Interestingly the structure of the dopant-C_iO_i defects is different with the Sn residing next to the O_i whereas the Si atom bonds with the C_i. The differences in the structure of C_iO_i defects in the vicinity of isovalent dopants are discussed.