<p>This work investigates residual defect populations in arsenic-ion-implanted HgCdTe epitaxial layers using focused ion beam–scanning electron microscopy (FIB-SEM) nanotomography. Nanovoids are identified as the predominant residual defect. Void sizes range from 4&#xa0;nm to 40&#xa0;nm, with depth distributions peaking near the projected range of implanted arsenic. A clear correlation between arsenic implantation fluence and void density is observed, with lower fluence reaching void density values on the order of 10¹⁰&#xa0;cm⁻³, corresponding to the detection of a single void within a typical infrared pixel volume. Additionally, linear dislocation-like features were identified, forming apparent networks that link individual voids within the implanted region. These results offer compelling evidence that FIB-SEM nanotomography provides the sensitivity and statistical reliability required to resolve and quantify low-density residual defects at the nanoscale, thereby offering a powerful tool to guide process optimization and ensure the crystal quality needed for high-performance HgCdTe-based infrared photodiodes.</p> Graphical Abstract <p></p>