Effects of Structural Disorder on the Electronic Properties of Silicon: Tight-Binding Calculations of Grain Boundaries

The atomic and electronic structures of tilt and twist boundaries in Si have been calculated by using the transferable semi-empirical tight-binding (SETB) method, and the relations between the local structural disorder and the electronic properties of Si have been obtained clearly. The odd-membered rings and the four-membered rings induce the changes of the shape of the local density of states (LDOS). The bond distortions generate the peaks at the band edges in the LDOS, and greatly distorted bonds induce the weak-bond states inside the band gap. The three-coordinated defect generates a deep state in the band gap, which is much localized at the three-coordinated atom. The five-coordinated defect generates both deep and shallow states. The deep state is localized in the neighboring atoms except the five-coordinated atom, although the shallow states exist among the five-coordinated atom and the neighboring atoms. Configurations of boundaries are very effective in order to clarify the effects of the local structural disorder in amorphous SI.