Phosphorus Doped Diamond Electron Emitter Devices
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1039-P09-04
Phosphorus Doped Diamond Electron Emitter Devices Natsuo Tatsumi, Akihiko Ueda, Keisuke Tanizaki, Yoshiki Nishibayashi, and Takahiro Imai Semiconductor Technologies R&D Laboratories, Sumitomo Electric Industries, LTD., 1-1-1, Koyakita, Itami, Hyogo, 664-0016, Japan ABSTRACT The authors developed a high current phosphorus doped diamond electron emitter device. The n-type diamond is known to have high electron emission properties. However, device fabrication on n-type phosphorus doped diamond had 3 difficulties. First, the authors have developed extremely sharp electron emitter tip fabrication technology to enhance electric field whose tip radius was as small as 2 nm, but the shapes of the emitter tips had randomness. In order to fabricate high yield device, homogeneity of emitter tips have to be improved. Second, because heavily phosphorus doped n-type diamond layer can be grown only on (111) diamond substrate which is as small as 3 mm, fabrication of highly homogeneous 3 dimensional structure such as gate electrode was very difficult. Third 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 homogeneous tip fabrication technique, a new large size composite wafer in which (111) single crystal diamond was buried in polycrystalline diamond, and a new electrode coated emitter tip structure 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 heavily 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 length 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 were same values. This means that electrode coating did not degrade the emission properties and electrons were emitted from the n-type 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.
INTRODUCTION Diamond is one of the wide band-gap semiconductor and its physical properties are superior to SiC and GaN. By the recent development of doping technology, application of diamond for electronic devices are expected. One of the most unique property of diamond
is negative electron affinity that allows electrons to emit easily from the diamond surface[1]. Electron emission properties from diamond have been reported by many researchers[2
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