Lithium, sodium, and copper in Hg0.78Cd0.22Te and CdTe-based substrates

Abstract

We present a theoretical examination of the behavior of lithium, sodium, and copper in Hg0.78Cd0.22Te and in CdTe. In both HgCdTe and CdTe, all three impurities are determined to incorporate predominantly on the cation sublattice for most pressures and temperatures, where all the impurities have acceptor levels. All three impurities have secondary incorporation as interstitials, where they all behave as donors. Under conditions present in low-temperature, mercury-saturated anneals, lithium and sodium are mobilized because of the relatively high interstitial fraction, lower solubility, and an exothermic impurity kick-out reaction when the material is subjected to an injection of mercury interstitials. Strain effects on the impurity incorporation are small and do not provide a strong driving force for these impurities to segregate. By examining the relative behavior of the impurities in CdTe and HgCdTe, we have derived prescriptions for maximizing gettering the impurities from CdTe-based sub-strates using a sacrificial HgCdTe epilayer, and for minimizing gettering from the substrates during epilayer growth.