Fermi-level pinning in Schottky diodes on IV–IV semiconductors: effect of Ge and C incorporation

We have investigated the phenomenon of Fermi level (E-F) pinning at the interface between tungsten and SiGeC alloys with 0 less than or equal to x less than or equal to 33% and 0 less than or equal to y less than or equal to 1.25%. In an attempt to throw lights on the mechanisms responsible for the Fermi level pinning, we have measured Schottky barrier dependence on composition, strain retained in the semiconductor and temperature. For pure Si, the Fermi level is pinned relative to the valence band-Phi(Bn) follows the bandgap variations with the temperature. On the other hand, the addition of Ge results in a Fermi level pinning relative to the conduction band-Phi(Bn) remains constant whatever the composition, the strain in the films and the temperature. The role of C is still puzzling. The addition of C does not modify the barrier in n-SiGe films but leads to a large decrease of the barrier height on n-SiC.