Si-rich W silicide films composed of W-atom-encapsulated Si clusters deposited using gas-phase reactions of WF6 with SiH4

We formed Si-rich W silicide films composed of Sin clusters, each of which encapsulates a W atom ( WSin clusters with 8 < n <= similar to 12), by using a gas-phase reaction between WF6 and SiH4 in a hot-wall reactor. The hydrogenated WSinHx clusters with reduced F concentration were synthesized in a heated gas phase and subsequently deposited on a substrate heated to 350-420 degrees C, where they dehydrogenated and coalesced into the film. Under a gas pressure of SiH4 high enough for the WSinHx reactant to collide a sufficient number of times with SiH4 molecules before reaching the substrate, the resulting film was composed of WSin clusters with a uniform n, which was determined by the gas temperature. The formed films were amorphous semiconductors with an optical gap of similar to 0.8-1.5 eV and an electrical mobility gap of similar to 0.05-0.12 eV, both of which increased as n increased from 8 to 12. We attribute this dependence to the reduction of randomness in the Si network as n increased, which decreased the densities of band tail states and localized states. (C) 2016 AIP Publishing LLC.