Electronic and transport properties of hydrogenated amorphous silicon

We have extended previous coherent-potential-approximation calculations of the electronic and transport properties of hydrogenated amorphous silicon (a-Si), in order to examine the effects of fully dispersed hydrogen in a-Si. The present calculation replaces random vacancies in the Si matrix by single H atoms instead of the four-H-atom clusters previously considered. In addition, to eliminate dangling-bond states in the gap we have introduced an ad hoc reconstruction of the lattice around the vacancy by effectively saturating the dangling orbitals with other Si atoms. Our results reinforce previous claims that an understanding of various experiments in a-Si:H can be obtained from first-principles calculations which neglect topological disorder and the precise configuration of the hydrogen atoms. The present calculations lead to an improved agreement with the photoemission and optical absorption data.