New semiconducting silicides assembled from transition-metal-encapsulating Si clusters

We synthesized amorphous films composed of transition-metal-encapsulating Si clusters (MSin: M = Zr, Nb, Mo and W) by deposition of hydrogenated MSinHx clusters onto solid substrates followed by annealing at 400-500 deg. C for dehydrogenation. The MSin (n = 7-20) cluster films are amorphous semiconductors with an optical gap > 0.4 eV and have larger electron and hole mobility than that of the hydrogenated amorphous Si (a-Si:H) film. In these films, while Si atoms form amorphous networks similar to those in a-Si:H films, the thermal stability is enhanced and the electronic disorder is reduced by the use of MSin clusters as the unit structures. Structure modeling by ab initio calculations for MSin films suggests that the encapsulated M atom works as a terminator of dangling bonds of the Si network.