Status of point defects in HgCdTe

This paper reviews the status of point defect studies in HgCdTe and presents new data on the characterization of impurities in CdTe, on shallow and deep acceptors in arsenic-doped HgCdTe, and on the ability of electron paramagnetic resonance (EPR) to detect defects in HgCdTe. Point defects are important in controlling carrier concentrations, minority-carrier lifetimes, and noise in HgCdTe. Shallow impurities from dopants are fairly well understood and their effects follow what is expected from the periodic table. Intrinsic defects such as the mercury vacancy, which is believed to act as a shallow acceptor, are less well understood and suffer from a lack of characterization techniques that can identify individual defects. Deep-level defects are present with concentrations proportional to the shallow acceptor concentrations. These centers often control lifetime and noise. Many of these have been electrically characterized, but not identified. Theoretical work by several groups to calculate defect levels has begun. At present, the errors in this work are larger than the HgCdTe band gaps, but the calculated trends are important. Experimental data on identified deep levels are needed both for guiding material improvement and for improving the theoretical modeling.