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IR cooled photodetectors need to operate at higher temperature to reduce their size, weight and power consumption (SWaP context). Their stability and image quality are then challenged by an extra electrical activity of crystal defects. Knowledge of defect populations is mandatory to improve the material quality of the epitaxial Hg1-xCdxTe (MCT) active layer and the Cd1-xZnxTe (CZT) substrate. Positron annihilation spectroscopy (PAS) with a slow positron beam was used to study near-surface open-volume defects profiles. Low and high momentum fractions (𝑆,𝑊) were used to characterize the Doppler broadening of the 511 keV electron-positron pair annihilation-line as a function of the positron implantation energy 𝐸. The results show that three regions can be identified beneath the surface of the as-grown non-optimized MCT layer. The quasi-linear relationship between the annihilation characteristics in the regions suggests that the defect populations mainly correspond tothe same open-volume defect in different concentrations. The probed defect is supposed to be related to the mercury vacancy. This hypothesis is discussed in an original way with near-surface elemental profiles using scanning transmission electron spectroscopy combined to energy dispersive X-ray spectroscopy (STEM-EDX).Afterwards, this approach is extended to CZT substrates showing that surface and bulk properties of those elaborated by LYNRED tend to the state of the art. A common open-volume defect is probed, in concentration estimated by Hall effect around 10 15 cm -3 and supposed to be related to the cadmium vacancy.