The carrier transport mechanism through thep-diamond/metal interface was studied by measuring specific contact resistances(&rgr;c)using a transmission line method for Ti, Mo, and Cr (carbide forming metals) and Pd and Co (carbon soluble metals) metals contacting to the boron-doped polycrystalline diamond films. Schottky barrier heights(&fgr;B)of around 0.5 eV were measured for the annealed contacts. The present result indicates that formation of thermally stable graphite layers at the diamond/metal interfaces upon annealing would pin the Fermi level of thep-diamond. This model led to the preparation ofin situOhmic contacts by depositing a thin diamondlike carbon on thep-diamond surface prior to metal deposition, and also to excellent Schottky contacts with breakdown voltages higher than 900 V. The present experiment concluded that the existence of a graphite layer at the diamond/metal interface controlled the electrical properties through thep-diamond/metal interface. ©1997 American Institute of Physics.