Carrier transport mechanism of Ohmic contact to p-type diamond

The carrier transport mechanism through the $p$ -diamond/metal interface was studied by measuring specific contact resistances ${\mathrm{(\rho }}_c)$ 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 ${\mathrm{(\phi }}_B)$ 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 the $p$ -diamond. This model led to the preparation of in situ Ohmic contacts by depositing a thin diamondlike carbon on the $p$ -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 the $p$ -diamond/metal interface.