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

We synthesized amorphous films composed of transition-metal-encapsulating Si clusters (MSi(n): M = Mo or Nb) by deposition of hydrogenated MSi(n)H(x) clusters onto silica substrates followed by annealing at 500 degrees C for dehydrogenation. The MoSi(n) (n = 7-16) cluster films are semiconductors with an optical gap >0.6eV and resistivity >1 Omega cm. In particular, the MoSi(12) cluster film has a large gap of 1.1 eV and resistivity of 120 Omega cm with high hole mobility of 32 cm(2)/(VS). 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 MSi(n) clusters as the building blocks. (C) 2008 The Japan Society of Applied Physics