Electrical properties of thin nanocrystalline diamond based structures

Electrical structures based on thin films of nanocrystalline diamond are described as well as their electrical properties. Diamond films with thickness between 0.25 and 1.0 μm and with average grain sizes of 300 nm and less are formed by microwave plasma-assisted chemical vapor deposition. Electrical properties of free-standing diamond films and of substrate mounted films are measured over a wide range of voltages with two-terminal electrical contacts. The films exhibited field-activated conductivity consistent with a Poole–Frenkel reduction in ionization energy associated with overlapping Coulombic potentials, well-modeled by Poole's Law. Metallization was performed on diamond films supported on the original silicon substrate and also on free-standing diamond. For the latter, the silicon substrate was removed by back-etching and the diamond film was transferred to a different structure. Both symmetrical and asymmetrical current–voltage characteristics have been obtained. Depending on the type of contacts, the rectification ratios of two-terminal structures range from 1 to 11,000 at high applied voltages.