A modified diffusion model for characterization of real I–V curve and charge collection efficiency of CdZnTe detectors

In the present paper, a modified diffusion model describing I–V curve of CZT detectors is proposed and used to characterize the electric field distribution. The detectors are considered to be fully depleted at high bias and incompletely depleted at low bias. For incompletely depleted condition, the inner electric field of CZT detector was separated into depletion region and neutral region. The neutral region was usually neglected in the traditional model. Two fitting parameters V_D and α are included in the proposed model, which can be fitted from I–V curve. The model is also extended to describe the electric field distribution. Furthermore, we figured out the calculated charge collection efficiency equations, which are consistent with experimental results. Experimental data from planar detectors indicate that the model could describe I–V curve precisely throughout a broad bias range. Serious electric field distortion in some planar detectors is attributed to the Schottky barrier. The relationship between charge collection efficiency (CCE) and bias voltage in these devices is not consistent with the Hecht equation. The difference may arise from the non-uniform electric field. The stronger effect of the Schottky barrier on electron collection efficiency is found in pixel detectors according to the non-uniform weighting potential, because for pixel detectors the induced charge is mainly contributed by the near anode region, which has low electric field under high cathode barrier.