Improved Schottky contacts to annealed 4H-SiC using a protective carbon cap: Investigated using current voltage measurements and atomic force microscopy

Schottky contacts on 4H-SiC surfaces, annealed at high temperature in the presence of a protective carbon cap, are compared to contacts fabricated by the same process, without the protective layer. Annealing at 1600 °C is required to electrically activate implanted dopants, but causes severe surface damage. We show using surface morphology studies, based on atomic force microscopy (AFM), that carbon-cap protected 4H-SiC had a considerably lower surface roughness than surfaces annealed without the protective cap. Nickel diodes fabricated on 4H-SiC samples, after removal of the carbon-cap using oxygen plasma etching, showed similar Schottky I(V) forward bias characteristics to contacts on samples that had not been annealed, and displayed similar reverse blocking voltages. Carbon cap protected samples also displayed lower reverse leakage currents than un-annealed samples. In contrast, contacts fabricated on unprotected surfaces, damaged by annealing at 1600 °C, displayed non-rectifying behaviour.