Point Defects in Covalent Semiconductors: A Molecular Cluster Model

A multiple-scattering-X alpha cluster model of tetrahedrally coordinated covalent semiconductors is discussed. In order to simulate the rest of the crystal at the cluster boundaries, all electrons filling dangling bonds are eliminated from the self-consistent calculations and transferred to a Watson sphere. This manner of simulating the "saturating effects" of the rest of the crystal is more practical than the usual procedure of terminating the atoms at the surface of the cluster with hydrogen atoms. The model is applied to perform the first self-consistent calculations of the electronic structure of vacancies and substitutional impurities in GaAs. The efficiency and accuracy of the model is demonstrated by calculating the well-studied states of an ideal vacancy in Si. The obtained results are in good agreement with other self-consistent calculations.