Structure change of ultra-thin Ni-deposited 6H-SiC(0 0 0 1)-3×3 surface by post-annealing

Clean 6H-SiC(0 0 0 1)-3×3 surfaces were deposited with 0.2–5 ML (1 ML: 1.21 × 1015 atoms/cm2) Ni at room temperature and then annealed at 400, 600 and 800 °C for 2 min. The surface structure was analyzed in situ by reflection high energy electron diffraction, photoelectron spectroscopy using synchrotron-radiation-light and high-resolution medium energy ion scattering. The surface morphology was observed ex situ by an atomic force microscope. The as-deposited Ni (1 ML) layer is disordered and does not react with Si and C. Annealing at 400 °C leads to formation of a NiSi2 layer and the samples annealed at 600 and 800 °C show a 4 × 4 superstructure coming from uniform stacking of 0.8–1.0 ML Ni-layer on which 0.4 ML Si atoms are located. For the sample annealed at 400 °C, a large number of C clusters appear on the surface probably due to bond-breaking of C–Si caused by chemical reaction of Ni–Si. The Si-2p core level shifts ΔEB observed depend on the deposited Ni-thickness. The lower binding energy shifts reflect an upward band bending generated at the interfaces and are determined to be 0.30 ± 0.10, 0.66 ± 0.10 and 1.02 ± 0.10 eV, respectively for 0.2, 1.0 and 5.0 ML Ni-deposited 6H-SiC(0 0 0 1). The Schottky barrier heights (SBHs) derived for the Ni(1 and 5 ML)-deposited samples are compatible with the SBH of the Schottky limit.