Dependence of contact resistance on metal electronegativity for B-doped diamond films

The contact resistance (Rc) measurements and microstructural analysis at the metal/diamond interfaces were carried out by depositing a variety of metals on the polycrystalline B-doped diamonds which were prepared by microwave plasma chemical-vapor deposition. The Rc values, which were measured by the transmission line method, were found to be dependent on the electronegativities of the metals, and the lower Rc values were obtained for the metals with higher electronegativity. The Rc values of the Ti and Mo contacts decreased upon annealing at elevated temperatures, and the TiC and Mo2C compounds were observed at the metal/diamond interfaces by cross-sectional transmission electron microscopy and x-ray diffraction. The reduction of the Rc values is believed to be due to creation of crystal defects induced by formation of the carbides. The present experiment suggests that the electronegativities of the metals would provide guidance to select Schottky and ohmic contact materials of future diamond semiconductor devices. However, we have a concern in use of semiconductive polycrystalline diamond films as their substrates.