THEORY OF ELECTRONIC-PROPERTIES OF AMORPHOUS-SILICON CARBON ALLOYS - EFFECTS OF SHORT-RANGE DISORDER

Homopolar (like-atom) bonding and threefold carbon coordination are found to drastically affect the electronic properties of amorphous silicon-carbon alloys. First-principles pseudopotential calculations based on amorphous geometries obtained from Monte Carlo empirical simulations show that incorporating C in Si-rich samples, in tetrahedral arrangements with heteropolar bonds only, increases the energy gap. This tendency is drastically reversed in C-rich samples because of graphitelike geometries. Like-atom bonds, in samples of all compositions, reduce the gap as well. The maximum gap is reached in samples of near-stoichiometric composition.