Surface roughness effect on the electrical characteristics of Pd/SiC nanocontacts

We report on the effect of the surface roughness of Pd nanostructures on the electrical characteristics (Schottky barrier height) of Pd nanostructures/SiC nano-contacts as probed by conductive atomic force microscopy. We produced Pd nanostructures on 6H-SiC surface by thermal-induced dewetting of a nanoscale-thick deposited Pd film. We changed the Pd nanostructures mean diameter <D> and mean surface roughness <s> by controlling the annealing temperature. Scanning Electron Microscopy and Atomic Force Microscopy allowed us to quantify <D> and <s> in various annealing conditions. In addition, current-voltage characteristics were acquired on single Pd nanostructure/SiC contacts by placing the tip of Conductive Atomic Force Microscopy on the Pd nanostructure. Typical rectifying Schottky characteristics were recorded from which the Schottky barrier heights Phi(B) were extracted. For ballistic Pd nanostructures (<D> approximate to 25 nm), Phi(B) was found to increase by increasing the nanostructures surface roughness above a critical value. For non-ballistic Pd nanostructures (<D> in the range 150-200 nm), no effect of the surface roughness was observed on FB. Regarding the ballistic Pd/SiC contact, the observed phenomenon is ascribed to the conducting electrons surface scattering relaxation mechanism and the surface roughness scattering mean free path for electrons is evaluated in the range 1.5-3.5 nm.