Nitrogen-oxygen complexes associated with shallow thermal donors in silicon

A structural model is described for the shallow thermal donors (STDs), which typically consist of seven identical absorption peaks that are caused by electronic transition. In the STD family, attention was paid to the 247 cm(-1) peak that appears to strongly depend on the condition of both the crystal growth and the annealing. We examined NO configuration and the six kinds of NO+O-i configuration. Semi-empirical molecular orbital calculations for these complexes suggested that not only the complex with the C-2V symmetry but also the asymmetric NO+O-i complexes could simultaneously exist in the Si crystal. We concluded that the 247 cm(-1) peak, which was highly unstable and behaved oddly during annealing, might be the NO complex and that the other six STD peaks might correspond to the six kinds of NO+O-i complexes. (C) 2008 The Japan Society of Applied Physics.