Ab initio studies of intrinsic point defects, interstitial oxygen and vacancy or oxygen clustering in germanium crystals

The formation energy (E-F) of the neutral vacancy (P) and of the neutral self-imerstitial (I), as well as the diffusion barrier of interstitial oxygen (0) in Ge is estimated using ab initio calculations. The stability of various structures of vacancy clusters (V-n) or oxygen clusters (O-n) was also estimated. The calculated formation energy of vacancies in Ge (E-F = 2.56 eV) is smaller than that in Si (E-F = 3.81 eV). On the other hand, the calculated formation energy of the self-interstitial at the < 110 > dumbbell site in Ge (E-F = 3.50 eV) is very close to that in Si (E-F = 3.51 eV). The diffusion barrier of oxygen in Ge is about 1.91 eV, which is far smaller than the barrier of 2.50 eV in Si. The binding energy E-b(V-n) of n isolated vacancies through the reaction n V -> V-n was also calculated. It was found that E-b(V-n) of V-n clusters in Ge is about 1.10 eV (n = 2), 1.97 eV (n = 3) and 2.70 eV (n = 4) smaller than E-b(V-n) of similar V-n clusters in Si. The obtained most stable configurations of 0, clusters (n = 2-4) in Ge are two, three and four staggered Ge-O-Ge bridges similar to the Si-O-Si bridges in Si. The binding energy E-b(O-n) of n isolated oxygen atoms through the reaction of nO -> O-n was calculated. It was found that E-b(O-n) in Ge is about 0.08 eV (n = 2), 0.21 eV (n = 3) and 0.38 eV (n = 4) larger than E-b(O-n) of the same O-n clusters in Si. These results indicate that V-n clusters are more stable in Si, while O-n clusters are more stable in Ge. (C) 2006 Elsevier Ltd. All rights reserved.