Charge injection devices

Abstract

The concept of Charge Injected Detectors (CID) has been developed and investigated by the CERN RD39 Collaboration for a considerable period of time. The CID is based on a balance between the trapping and detrapping processes in heavily irradiated semiconductor detector material. Radiation-induced defects trap charge carriers. The counter process of trapping, detrapping, is exponentially dependent on temperature. Thus, if the temperature is lowered, the trapped charge may occupy the radiation defect for considerably long time. This modifies the electric field distribution in an irradiated semiconductor. The trapped charge results in a continuous electric field through the entire thickness of a detector. The experimental results from RD39 show that a standard silicon strip detector, irradiated to 1×1015 neq/cm2 fluence, operated under CID mode has a relative charge collection efficiency (CCE) more than 33% while having a signal-to-noise (SNR) being slightly less than than 10. The CID operation of such a sensor requires a temperature of about -500C. The amount of injected forward current is comparable with the leakage current of a similarly irradiated detector operated with reverse bias voltage at about -200C.