Deactivation mechanism of In atoms doped in a Si crystal and reactivation due to codoping with B and C

We present results of first-principles calculations to clarify the activation and deactivation mechanism of indium (In) atoms in silicon (Si). The interaction between In atoms is found to be attractive and leads to spontaneous formation of the stable and electrically inactive nearest neighbor substitutional (NNS) In2 cluster, which is responsible for the much lower electrical activity compared with that for the boron atoms in Si. An elemental process of the formation of the NNS In2 cluster is found to be exothermic and its activation barrier is 0.7 eV, which is comparable to that (0.5 eV) of the kick-out reaction from an interstitial In to a substitutional In with an interstitial Si. We found that codoping boron (B) and carbon (C) with In makes the inactive In2 cluster unstable, and is efficient to increase the electrical activity. The activation/deactivation mechanism of In is relevant to electronic and elastic energy of the clusters (In In,In B,In C), which is clearly explained in the framework of the tight-binding approximation. In addition, we present the results of calculations for the vibrational properties of In B and In C clusters in Si.