The hydrogenated amorphous silicon/nanodisperse metal (Simal) system - Films of unique electronic properties

The a-Si:H/metal systems (SIMALS) were prepared as a-Si:H/V/a-Si:H or a-Si:H/Mo/a-Si:H trilayers and multilayers of a-Si:H/Mo or a-Si:H/Ti by PCVD, sputtering and thermal evaporation, respectively. Structural investigations performed on these films by scanning force microscopy, cross-sectional TEM and X-ray techniques indicate that SIMALS contain metal nanoclusters and an intermixed silicon-metal phase. The temperature dependence of the conductivity is described by sigma=sigma(0) exp[-(T-0/T)(1/2)] with T-0 ranging 100 K to 4 X 10(4) K. An electric field, typical of 100 V/cm applied to the samples in a coplanar electrode configuration results in an increase of the conductivity at room temperature from 10(-6) to 1 (Omega cm)(-1), which is reversible by annealing. This switching is accompanied by large fluctuation of the current. The electrical behavior of the SIMALS is compared to in-situ measurements on Mo-films on a-Si:H.