Electronic structure of a single neutral ideal phosphorus vacancy in GaP

The multiple-scattering Xalpha molecular cluster model is used to carry out self-consistent calculations of the electronic states of an isolated P vacancy in GaP. A fully occupied singly degenerate a1 level and a threefold-degenerate t2 level occupied by one electron are found within the band gap. This configuration indicates that the centre is unstable with respect to Jahn-Teller distortions. The vacancy states a1 and t2 are quite extended showing an appreciable charge distribution in the next-nearest neighbours of the vacancy (P atoms). The role played by these results in the explanation of the properties of the GaP:O centre is discussed.