n-Type contact of Schottky barriers at two-dimensional (2D) materials/metal interfaces is a usual formalization in the modern FETs applications. It is common to modulate it from n- to p-type through some specific methods. In this work, we came up with two new intrinsic p-type contacts of graphene-GeC/GeS and further tune them from p-type to n-type by external electric fields. It proved that the electronic properties of graphene and GeC/GeS can be roughly preserved for the weak van der Waals (vdW) interaction. p-Type contacts with relatively small barriers are formed at g-GeC/GeS heterointerfaces. After external electric field applied, the Schottky barrier can be effectively tuned by different external electric and the p-type contact further turns into n-type. Variation of the Schottky barriers indicated a partial pinning for interfaces of g-GeC/GeS. This is because the interfacial states between graphene and GeC/GeS hardly exists. The barrier height of g-GeC/GeS and the corresponding contact type can be flexibly tuned, which is of great importance in the design of novel transistors-based 2D materials. Searching for novel nanoscale electronic equipment based on 2D materials is a hot topic in the current study. This work would provide meaningful guidelines for nanoscale devices.