Electronic structure and metal-insulator transition in amorphous Pd-Si alloy films

The PdxSi100-x system forms a homogeneous amorphous phase over a wide range of composition (0 less than or equal to x less than or equal to 91, excluding regions near PdSi and Pd2Si) when the alloy is deposited on a substrate by sputtering at ambient temperature. The electrical conductivity of the amorphous alloy changes characteristically with Pd concentration from a semiconductor to a metal, the transition taking place at x(c) approximate to 12. UPS valence band spectra show that the density of states at the Fermi level is minimal for x < x(c), but emerges abruptly for x greater than or equal to x(c). AES SiL(2,3) VV spectra show that covalent Si-Si bonding is gradually reduced and replaced by metallic Pd-Si bonding as the concentration increases beyond the transition region. Relationships between the conducting properties and electronic structure of the amorphous alloys are discussed in three characteristic ranges of Pd concentration.