Microstructural defects in chlorine-doped cadmium telluride crystals (CdTe:Cl) can affect performance of CdTe-based radiation detectors. To study this, we produced a CdTe-based X-ray detector operating in integration mode. Its response under irradiation shows that sensitivity is non-uniform, dark-current maps were also observed. These indicate that charge carrier transport is heterogeneous. Advanced characterization tools, such as Infrared (IR) transmission and reflection microscopy and diffraction topography, were used for bulk and surface investigations. A clear correlation was established between the distribution of linear defects, such as dislocations and sub-grain-boundaries, and the localization of zones of non-uniform dark-current and photo-current in the sample.