Native Point Defects in HgCdTe Infrared Detector Material: Identifying Nonradiative Recombination Centers from First Principles

We investigate the native point defects in the long-wavelength infrared (LWIR) detector material Hg_0.25Cd_0.25Te using a dielectric-dependent hybrid density functional. The dielectric-dependent hybrid functional allows for an accurate description of the band gap (E_g) for Hg_1-xCd_xTe (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 the two isoelectronic cation vacancies, namely V_Hg and V_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 near the valence-band maximum (VBM). Meanwhile, the cation vacancies exhibit a deep charge transition level (-/2-) that is situated at E_g/2 above the VBM, which is characteristic of nonradiative recombination centers that can be a major limiting factor affecting device performance. Our study does not support the assignment of other native point defects (such as mercury interstitial) as the origin of deep levels in p-type LWIR MCT.