Effects of non-uniform electric field on the charge collection efficiency in radiation detectors: Deviation from Hecht formula

Abstract

The Charge Collection Efficiency (CCE) of a radiation detector under a non-uniform electric field has been examined by developing a semi-analytical and a numerical model. We consider the Carrier Packet Drift Analysis for the semi-analytical model and a numerical solution of the continuity and Poisson‘s equations for the numerical model. The space charge due to ionized dopants and the trapped charges of photogenerated carriers in the bulk photoconductor layer of the detector are considered. We analyze the electric field distributions and CCE of the detector under various charge carrier transport parameters and detector operating conditions. The CCE under the non-uniform electric field deviates significantly from the uniform field case as determined by the Hecht Collection Efficiency (HCE) formula. In most cases, the CCE under the non-uniform electric field deteriorates as compared to HCE. However, the CCE under the non-uniform electric field can also be improved for certain values of normalized carrier lifetimes (ratio of carrier lifetime to its transit time) provided that the radiation (photons or particles) absorption occurs mostly near the radiation-receiving electrode. The theoretical model has been applied to the published experimental results in perovskite x-ray detectors for general radiographic applications and found good agreement.