Phosphorus Doped Diamond Electron Emitter Devices

The n-type diamond is known to have high electron emission properties. However, device fabrication on n-type phosphorus doped diamond had 2 difficulties. First, because highly phosphorus doped n-type diamond layer can be grown only on very small (111) diamond substrate, fabrication of highly homogeneous 3 dimensional device such as gate electrode was very difficult. Second problem was that the resistivity of n-type diamond was still over 100 Ω cm and too high for high current electron emission devices. To solve these problems, we developed a new large size composite wafer in which (111) single crystal diamond was buried in polycrystal diamond and a new electrode coated emitter tip structure for conduction support only whose apex was exposed from the electrode. N-type phosphorus doped diamond was grown on the 15 mm composite diamond wafer with high PH3/CH4 concentration of 20% and highly doped active layer was grown on the embedded (111) single crystal. Sharp emitter tip arrays were fabricated by etching the n-type diamond. Electrodes were coated on these tips and exposed area of diamond was less than 200 nm from the apex of the tip. Gate electrodes were fabricated for each emitter tips. Electron emission of these devices were measured in the vacuum of 10−7 Pa. The threshold voltage of the n-type diamond device was 60 V which was lower than 100 V of the p-type diamond device. The threshold voltage of n-type diamond with and without electrode coatings did not changed. This means that electrode coating did not affect the emission properties and electrons were emitted from the diamond surface. The emission current was enhanced by 2 orders by the electrode coatings and total emission current from 1 mm2 reached 1103 mA. This high emission current electron source enables applications to microwave tubes, electron beam processing and integrated micro vacuum devices.