Photoelectric and electrical responses of several erbium silicide/silicon interfaces

In this work, photoelectric yield and electrical properties of several types of epitaxial erbium silicide on silicon Schottky diodes are studied. Different preparation conditions are used simultaneously on n- and p-Si(111) substrates for the 200 Å thick silicide films. A last type of sample consists in 1.3 monolayer of epitaxial silicide with 3×3 superstructure on the Si substrate and covered by silver on the top. Photocurrent measurements are done as a function of photon energy at several temperatures. All these samples show barrier heights near 1 eV on p-type Si, even for the interface comprising only 1.3 monolayer of silicide whereas barrier heights on n-type Si span the range from 0.28 to 0.67 eV for this last kind of sample, the sum of the barriers always exceeding the silicon band gap. These photoelectric results are confirmed by electrical characterisations. All these results show that the Fermi level is pinned 0.1 eV below the conduction band edge on p-type Si but shifts to various positions lower within the band gap on n-type Si. This fact leads to the hypothesis of a density of interface states close to the charge change in the Si depletion zone from p- to n-type, namely 1012 eV−1 cm−2. Although some inhomogeneities and defects at the interface are detected by electron microscopy for samples annealed at 750°C, Fermi level position seems rather insensitive to the structural details of the interface while the silicide thickness plays a role on n-type Si.