RESISTIVITY AND SUPERCONDUCTING TRANSITION-TEMPERATURE OF VERY THIN AMORPHOUS TUNGSTEN GERMANIUM FILMS DEPOSITED BY CHEMICAL-VAPOR-DEPOSITION

Very thin amorphous W0.7Ge0.3 films have been deposited on silicon sub strates by a novel chemical vapour deposition process. For films with a thickness (d) smaller than 10 nm, the observed increase of the resis tivity with decreasing film thickness is well described by percolation theory. When d>10 nm, the resistivity is independent of the film thic kness (rho0 = 191 muOMEGA cm). The superconducting transition temperat ure (T(c)) of thick films (d>95 nm) is 4.9 K. The observed reduction o f T(c) with decreasing film thickness (d<95 nm) scales linearly with t he sheet resistance and is well described by the theory of Maekawa and Fukuyama which takes into account the effect of weak electron localis ation on the properties of dirty superconductors. Films with 1.3<d<3.7 nm are not homogeneous and do not become superconducting. The resisti vity and the superconducting transition temperature of thick films (d> 95 nm) compare very well with the results obtained by Kondo for 500 nm thick amorphous W0.7Ge0.3 films made by sputtering. For the applicati on of amorphous W0.7Ge0.3 films in submicron superconducting devices, the excellent conformal growth of CVD films might be an important adva ntage.