1ST PRINCIPLES CALCULATION OF NATIVE DEFECT DENSITIES IN HG0.8CD0.2TE

We use a quasichemical formalism to make quantitative predictions of the native point defect densities in Hg0.8Cd0.2Te. The electronic contribution to the defect-formation free energy is calculated using the self-consistent first-principles full-potential linearized muffin-tin orbital method and the local-density approximation (LDA). A gradient correction is added to the LDA result so that absolute reference to the chemical potential of the mercury vapor phase can be made. A Green's function approach based on a valence force field plus a point Coulomb model is used to calculate the vibrational contributions to the defect free energy (both energy and entropy). We find the double acceptor mercury vacancy is the dominant defect, in agreement with previous interpretations of experiments. The tellurium antisite is also found to be an important defect in this material. Predictions of the low-temperature hole concentrations are made as a function of annealing temperature and compared with available experiments. The order of magnitude of our predictions agrees well with experimental results, and discrepancies can be attributed to contributions to the free energy that we have neglected or to inaccuracies in the intrinsic reaction constant used. Suggestions for further experimental work are made.