We construct the in-plane heterojunctions of Boroβ12/SiC and Graphene/SiC to study the effect of different interface contacts on the electronic properties using first-principle calculations. The metalization of SiC at the contact interface is found in both heterojunctions, and two heterojunctions show high charge inject efficiency. The Boroβ12/SiC possesses p-type Schottky contact, while Graphene/SiC shows n-type Schottky contact. When the electric field is applied to two heterojunctions, the Schottky barrier height and contact type are changed, and the Ohmic contact is achieved at negative electric field. The results propose a way to design planar SiC-based electronic device with tunable interface contact. Figure-projected local density of states and transmission spectra of (a) Boroβ12/SiC and (b) Graphene/SiC. The Boroβ12/SiC shows p-type Schottky contact with SBH of 1.071 eV, while Graphene/SiC presents n-type Schottky contact with SBH of 1.021 eV. It can be seen that the metalization of SiC at contact interface in Boroβ12/SiC is more clear than Graphene/SiC. There are fewer metal-induced gap states in the bandgap in Graphene/SiC than Boroβ12/SiC, suggesting the better electric contact in Graphene/SiC. Combined with ΦTB and SBH, Graphene/SiC has a good electronic transport. [ABSTRACT FROM AUTHOR]