The electron field emission properties of planar SiC/Si heterostructures with various surface morphology formed by high dose C+ implantation into Si using a metal vapor vacuum arc ion source were investigated. An implant energy of 35keV was used with doses of 8×1017, 1×1018 and 1.2×1018 ions/cm22 with subsequent annealing in Ar at 1200℃ for various times. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy showed that a thin stoichiometric SiC surface layer is formed and the surface work function is about 4.5eV. Atomic force microscopy indicated that the size and density of the densely distributed small protrusions formed on the surface vary with preparation conditions. Results showed that there is an optimum annealing time for the corresponding implant dose at which a remarkably low turn-on field of about 1V/mm is observed. The density and size of the small protrusions on the surface are believed to be the main factors affecting the field emission properties.