Advanced Theoretical Models for Charge Collection in CdTe Radiation Detectors: a comparison based on experimental data

CdTe detectors performances are limited by trapping of carriers in crystal defects and an accurate evaluation of charge transport properties in the detector is essential to characterize the semiconductor quality, the detector technology and to determine the expected resolution of the system. In this paper, we present a comparison among different theoretical models for charge collection applied to the same experimental data. These advanced models, unlike the classical Hecht law, take into account second order effects like nonuniform absorption of the photons, influence of the surfaces and of localized spatial charge. The validity of these models and their limits have been evaluated on the base of experimental data acquired with a Schottky CdTe pixelated detector irradiated with an $^{241}$ Am X-$\gamma$ source. Mobility-lifetime products for electrons in the bulk have been derived and compared. Moreover, surface recombination velocity and shape of the internal electric field are considered, allowing to assess the quality of the crystal and of the technology.