The nature of ion-implanted contacts to polycrystalline diamond films

摘要

Electrical conductivity through high resistivity undoped polycrystalline CVD diamond layers is measured for different electrical contacts to the surface. In particular high dose ion implanted contacts. which result in graphitization of the implantation affected material are compared with metallic contacts. It is found that the resistivity of the diamond layer measured with implanted contacts is always smaller by one to two Orders of magnitude then that measured with metallic contacts. This phenomenon is found for both boron and carbon implanted films, hence it must be due to Implantation related damage to the diamond. Heat treatment of the implanted contacts (700 deg C) followed by chemical graphite removal results in the disappearance of the difference between the current leakages measured with implanted and metallic contacts, yielding for both cases very high resisitivities It is speculated that improved contact to grain boundaries due to the ion-implantation related surface graphitization results in an intimate contact to grain boundaries. This improves charge injection to the more conductive grain boundaries leading to the observed phenomenon. High-resolution scanning electron microscopy and micro-Raman spectroscopic investigation of regions between the graphitized layer and grain boundaries fail to reveal any noticeable changes in the inter-grain implantation affected near surface region. The advantages or disadvantages of the use of implantation-graphitized contacts to diamond based radiation detectors are discussed.