Origin and nature of gap states in a-Si : H alloys

The origin and nature of gap states due to intrinsic defects such as weak bond, bent bond and charged configuration have been examined in a-Si: H alloys with several kinds of Si₄₇ atomic clusters which are cut from continuous random networks, and simple ones of Si₈H₁₈ and Si₁₇ using LCAO MO CNDO method. The results show that two weak bond states disperse in both sides of band gap depending on the strength of the bond and influenced by extra charges. The bent bond states appear between the top of valence bond and the centre of the gap. The topological disordering can induce the gap states at any position within the band gap. According to this result, the E_x and E_y feature of gap states in the experiments of Spear et al. [1] can be understood clearly, and other recent experiments are explained reasonably. © 1989.