Necessary contact conditions for charge injection development into KBr single crystals

We have studied the current vs time behaviour of KBr single crystals by applying a constant voltage between a pointed cathode and a flat anode at constant temperature. The obtained curves are characterized by three or four different zones. We report here very detailed results on the first one. We conclude that in this zone the current through the crystal is purely ionic. As a consequence of this ionic transport, K atoms accumulate at the pointed cathode to form a new electrode. This acts as an injecting contact for electronic current. Electron injection currents and, therefore, colour center clouds that developed upon the formation of this new injecting contact, mark the start of zone II of the current vs time curve. Simple equations are proposed to explain the kinetics of zone I. Experiments by other authors are also analyzed. Finally, a discussion on the simpler experimental conditions required to create the new injecting contact is presented. Results on zones II and III will be published in the near future.