Electronic Structure and Metal-Insulator Transitionin Amorphous Pd-Si Alloy Films

Abstract

The Pd_xSi_100-x system forms a homogeneous amorphous phase over a wide range of composition (0≤ x≤ 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≈ 12. UPS valence band spectra show that the density of states at the Fermi level is minimal for xc, but emerges abruptly for x≥ 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.