Native point defects in HgCdTe infrared detector material: Identifying deep centers from first principles

We investigate the native point defects in the long-wavelength infrared (LWIR) detector material Hg$_{0.75}$Cd$_{0.25}$Te using a dielectric-dependent hybrid density functional combined with spin-orbit coupling. Characterizing these point defects is essential as they are responsible for intrinsic doping and nonradiative recombination centers in the detector material. The dielectric-dependent hybrid functional allows for an accurate description of the band gap ($E_g$) for Hg$_{1-x}$Cd$_{x}$Te (MCT) over the entire compositional range, a level of accuracy challenging with standard hybrid functionals. Our comprehensive examination of the native point defects confirms that cation vacancies $V_\text{Hg(Cd)}$ are the primary sources of $p$-type conductivity in the LWIR material given their low defect formation energies and the presence of a shallow acceptor level ($-$/0) near the valence-band maximum (VBM). In addition to the shallow acceptor level, the cation vacancies exhibit a deep charge transition level (2$-$/$-$) situated near the midgap, characteristic of nonradiative recombination centers. Our results indicate that Hg interstitial could also be a deep center in the LWIR MCT through a metastable configuration under the Hg-rich growth conditions. While an isolated Te antisite does not show deep levels, the formation of $V_\text{Hg}$-Te$_\text{Hg}$ defect complex introduces a deep acceptor level within the band gap.