Development of a charge collection model in CdZnTe detectors and its application to Gamma-ray spectrum

Abstract

The performance of a cadmium zinc telluride (CdZnTe) room temperature radiation detectors is mainly limited by the charge transport properties. In this study, charge transport properties were investigated through three models and a simple model for the charge collection process in CdZnTe radiation detectors of m-i-m diode structure was developed. The developed model can take the input variables of material properties, such as mobility and lifetime of electrons and holes, as well as the operation parameters, such as the applied bias voltage, pulse shaping time, and the incident direction and the energy of gamma-rays. Using the developed model, the pulse height spectra of mono energy gamma-rays are analyzed. The measured charge collection efficiency was agreed well with the model calculations, and the distortion of the photo-peak spectrum was understood well by the charge collection model. The developed model will be useful in quick evaluation of the CdZnTe detector diode as well as the design of optimal detectors for specific applications, such as the surgical probe, the detector array for X-ray CT, and the two-dimensional detector for gamma camera and positron emmision camera. And using the three charge transport models, it was found that the transport phenomena of electrons can be sufficiently explained by drift and trapping, and holes are transported with a dispersive nature. The major transport parameters are measured as follow: electron mobility is ~ 1000 ㎠/Vsec; hole mobility is ~120 ㎠/Vsec; electron lifetime is ~0.9μsec; hole lifetime is ~0.2 μsec.