Ion-induced charging processes in CVD diamond films: cold cathode versus charged particles detector

摘要

Ions may create large numbers of electron-hole pairs while in motion and slow down in a semiconductor. These electrons can either leave the material as secondary electrons, and be collected on an external positively biased electrode placed away from the surface, or can be collected on electrodes placed on the surface. The first process is involved in ion-induced electron emission (IIEE) whereas the second has to do with the detection of charged particles in semiconductor detectors. For the case of diamond, charges collected due to electrons and holes liberated by ions moving in the material show a rapid decay of the signal with increasing number of impinging ions. This has been observed both for the case of secondary electron emission, in which a drastic reduction in the emitted current occurs under ion bombardment, and in the reduction of charge collection efficiency in a diamond detector during charged particle detection. This decrease of induced earners poses a serious limitation to the otherwise excellent promise that diamond offers for detection of fast-moving charged particles. In the present work, the results of a series of experiments, in which the low-dose response of diamond as a detector for 5.5 MeV alpha particles is compared to those in which diamond is used as a cold cathode for the emission of secondary electrons, are presented. The possibility that both phenomena are related, both having to do with local charging of the diamond by the large number of earners produced by each impinging ion, is discussed. Ways of overcoming the problem are demonstrated.