Diamond p-i-n-nanoC Diodes for Electron Emitters

Electron emitters are widely deployed in traveling wavetubes (TWTs) for communications, radar applications, and scientific apparatus like free electron lasers. These instruments typically utilize cathodes that release an electron current through application of thermal energy or high electric fields. A novel electron emitter approach exploits the negative electron affinity surface of diamond in a modified semiconductor p-i-n diode. Under a forward bias electrons are injected into the conduction band of the diamond diode and a fraction are emitted into vacuum. Electron emission occurs at room temperature and low electric fields. We have prepared a modified diamond p-i-n diode that included a highly conducting nanostructured carbon (nanoC) contact layer utilizing plasma-enhanced chemical vapor deposition (PECVD) on a single crystal boron doped substrate. Emitter devices with various geometries were then fabricated using photo-lithography. After a hydrogen passivation step individual devices were characterized in vacuum. Under a forward bias the p-i-n-nanoC diodes displayed light emission indicative of bipolar transport. With a typical diode current of 0.1A an electron emission current approaching 0.4mA was measured from a single device sized 1.2mm x 0.2mm.