High Current p-i-n-nanoC Diamond Diodes for Electron Emission

Conventional electron sources utilize high temperatures or high electric fields to extract electrons from a solid where the emission current can be described by the thermionic Richardson-Dushman and the field emission related Fowler-Nordheim relation, respectively. A novel approach for electron sources can exploit aspects of diamond as an electronic material where n-type and p-type doping in conjunction with negative electron affinity properties allows engineering of p-i-n solid state diodes for direct electron emission. We prepared p-i-n-nanoC diamond diodes on single crystal diamond substrates by plasma-enhanced chemical vapor deposition and utilized a nitrogen incorporated nanostructured carbon (nanoC) layer as an electrical contact layer. The emitter structures were prepared using lithography to prepare mesa-etched structures with varying geometry. The final device was exposed to a hydrogen plasma that induced the negative electron affinity (NEA) properties of the devices. Application of a forward bias established a current through the device and the observation of light emission was an indication of bipolar transport and attributed to the free exciton recombination in diamond. With an increase in the diode current an increase in the electron emission current was observed. For a small emitter structure sized 1.2 x 0.22 mm a diode current of 1A corresponded to a current density of 408A/cm
²
. This diode current effected an electron emission current of about 0.7mA corresponding to an electron emission current density of 0.285A/cm
²
.