Synthesis of New Amorphous Semiconductors Assembled from Transition-Metal-Encapsulating Si Clusters

We synthesized amorphous films composed of transition-metal-encapsulating Si clusters (MSin: M=Mo or Nb) by deposition of hydrogenated MSinHx clusters onto silica substrates followed by annealing at 500 ?C for dehydrogenation. The MoSin (n=7?16) cluster films are semiconductors with an optical gap >0.6 eV and resistivity >1 ? cm. In particular, the MoSi12 cluster film has a large gap of 1.1 eV and resistivity of 120 ? cm with high hole mobility of 32 cm2/(V s). In these films, Si atoms form amorphous networks similar to those in hydrogenated amorphous Si but the electronic disorder is reduced by the use of MSin clusters as the building blocks.