Carbon nanotubes based photocathodes for multisource X-Ray generators

J.-P. Mazellier
Thales Research & Technology, FR

Keywords: carbon nanotubes, field emission, photocathode

Summary:

Carbon nanotubes (CNT) cathodes are cold field emitters. CNT photocathode consist in combination of CNTs with photodetectors. In a CNT photocathode, the photodetector limits the current that the CNT emit under electric field. As a result, by controlling impinging light power on photodetectors, the photocathode current can be controlled. Two strategies are possible: to couple CNTs with photodiode elements or photoresistive materials. Our work focused on the fabrication of vertically aligned CNT, grown by PECVD, coupled with photodetectors in an array configuration . A first case of study concerned silicon p-i-n photodetectors with good responsivity at 650nm (red light). CNT based photocathodes have been demonstrated in our group. First results demonstrated an ON-OFF ratio up to 30. Simulation work points out the role of the surface leakage in dark current and electrostatic control. Consequently, we improved the process in order to maximize ON-OFF ratio. We also focused on CNT-diamond photocathode. Diamond is a high resistivity material with good responsivity at 266nm (deep UV light) [2]. Diamond reveals to be an excellent diffusion barrier to nickel, allowing for direct CNT growth. We studied the performances of this innovative structure in terms of photocathode characteristics.