Self-consistent electronic structure of realistic models of amorphous hydrogenated silicon

Abstract

The self-consistent pseudopotential method has been used to calculate the electronic structure of periodic models of amorphous hydrogenated silicon containing 7-13 at.% of hydrogen, both as monohydride and as dihydride. The total density of states, involving almost entirely the silicon valence electrons, has two unequal maxima in the occupied region, followed by a region of very low (possibly zero) density before rising again rapidly in the energy range that is empty of electrons in the ground state. These features vary only a little from one example to another, and are not very dependent on the number of atoms in the repeating unit or the number of plane waves in the basis set. The distribution in energy of the occupied states having large densities near the hydrogen atoms is found to be quite different, depending on whether the atoms are attached singly to silicon or in pairs. In all cases, the electron density along the Si-H axes shows the variation expected for filled bonding states and empty antibonding states. In general, states amounting to a small fraction of the total appear just below the bottom of the valence band. These are associated in at least one case with a three-center bond joining a hydrogen atom and two silicon atoms.