How to fabricate low-resistance metal-diamond contacts

Three types of mesa etched contact resistance test structures with Al Si , TiAu, TiWN-Au contacts are compared. The contact resistivity was calculated using transmission-line model (TLM) theory which is fully applicable to diamond. For Al Si contacts the lowest contact resistivity was obtained after annealing at 500 °C in dry nitrogen. The lowest contact resistivity for as-deposited contacts was found for TiAu. In general, the contact resistivity drops with increasing levels of B dopant and depends on the metallization scheme. The dependence of the contact resistivity on the surface concentration of B for as-deposited Al Si contacts can be fitted by a power-law indicative of spatial inhomogenous areas in the contact region leading to an additional spreading resistance component. The contact resistivity depends exponentionally on the operating temperature for as-deposited Al Si contacts but the thermal coefficient is independent of the doping level for heavily B-doped diamond films, which is typical for tunneling.