Structural and electronic properties of carbon-hydrogen complex in silicon

We have investigated the atomic configurations, the stabilities, and the electronic structures of the carbon-hydrogen (C-H) complex in silicon for different charge states, based on the pseudopotential-density-functional method in a supercell geometry. For the neutral and positive charge states, we have found that the bond-interstitial (B) site between a substitutional carbon atom and the adjacent silicon atom is most stable for hydrogen. The antibonding sites of the carbon (AB(C)) and the silicon (AB(Si)) are metastable. In the negative charge state, the tetrahedral (T_d) interstitial site, in which the hydrogen is dissociated from the carbon, is as stable as the B-site for hydrogen. The impurity states due to the complex, except for the state in the AB(C)-configuration, are virtually identical to those due to a hydrogen atom at the same atomic sites without carbon. Based on our results, we discuss the structural change and the dissociation of the C-H complex accompanying the change of the charge state.