LITHIUM, SODIUM, AND COPPER IN HG0.78CD0.22TE AND CDTE-BASED SUBSTRATES

We present a theoretical examination of the behavior of lithium, sodiu m, and copper in Hg0.78Cd0.22Te and in CdTe. In both HgCdTe and CdTe, all three impurities are determined to incorporate predominantly on th e 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, lit hium and sodium are mobilized because of the relatively high interstit ial fraction, lower solubility, and an exothermic impurity kick-out re action when the material is subjected to an injection of mercury inter stitials. Strain effects on the impurity incorporation are small and d o not provide a strong driving force for these impurities to segregate . By examining the relative behavior of the impurities in CdTe and HgC dTe, we have derived prescriptions for maximizing gettering the impuri ties from CdTe-based substrates using a sacrificial HgCdTe epilayer, a nd for minimizing gettering from the substrates during epilayer growth .