VACANCY FORMATION AND EXTRACTION ENERGIES IN SEMICONDUCTOR COMPOUNDS AND ALLOYS

Extraction energies for diamond and zinc-blende semiconductor compounds and pseudobinary alloys are calculated using a tight-binding cluster method, where the final state of the removed atom is in a free-atom state. The extraction energies provide a convenient reference from which other final states of the removed atoms can be calculated. In the elemental and compound semiconductors, the convergence of the cluster calculation was verified using a Green's function calculation with the same Hamiltonian. For the elemental semiconductors, vacancy (or Schottky defect) formation energies, in which the final state of the removed atom is on the surface, have been calculated. For pseudobinary alloys of the form A1-xBxC, we find extraction energies to be very sensitive to the local environment, exhibiting a nonlinear variation between the A- and B-rich local environments; the nonlinearity is especially pronounced for the removal of a C atom. Nonlinearities are found to arise primarily from the occupation of localized vacancy states. The impact that these alloy variations will have on measurable properties are discussed.