Field emission mechanism from undoped chemical vapor deposition diamond films

Abstract

We have investigated the field emission mechanism for nominally undoped diamond films with a thickness ranging from 3.2 to 27.5 μm, epitaxially grown on low p-doped Si(001). The experiments were performed in a field emission scanning microscope, which allows the investigation of μm-sized spots on cm2-sized samples. First, all samples were heated at 300 °C, resulting in electrically insulating properties. Then, current I versus voltage U measurements in electrode contact mode were performed at different temperatures and for both polarities as well as in noncontact mode for different electrode gaps. For local current densities up to 0.5 A/cm2 the field emission was limited by the diamond bulk properties and not by the surface barrier. Conduction through the bulk occurred by a Poole–Frenkel process for traps with overlapping Coulomb potentials. A thermally assisted electron hopping over the Coulomb barriers was proven and an activation energy of 0.43 eV and a trap density of 7.1×1018/cm3 were derived.