Energetics of antiphase boundaries in GaAs

Structural energies of antiphase boundaries in GaAs are studied theoretically using a pseudopotential density-functional approach. The formation energy is calculated for several antiphase boundaries having different orientation and stoichiometry. The lowest-energy (110) and (001) boundaries are predicted to be stoichiometric (having no net excess of As or Ga atoms at the interface), while the (111) antiphase boundary is predicted to be nonstoichiometric. The (110) boundary has the lowest formation energy per unit area of those studied. Simple models of the energetics are discussed and compared with the first-principles results. Simple wrong-bond counting is found to be grossly inadequate. An extended model of pair interactions involving a Madelung sum for distant neighbors is formulated and found to give a reasonable description of stoichiometric antiphase boundaries. Nonstoichiometric antiphase boundaries require special treatment, as they generally have a partially filled donor or acceptor band and should be treated as metallic.