The electronic properties of uncharged Ga monovacancies in (110) surfaces were deduced from voltage-dependent scanning tunnelling microscope images. Such a monovacancy had a reduced density of states above the neighboring P atoms in images which were not affected by localized defect states. This suggested the existence of an inward relaxation of the P atoms. At low voltages, 3 of the 4 neighboring empty dangling bonds extended into the vacancy site in empty-state images. In images of the occupied states at low voltages, the neighboring P atoms exhibited an increased density of states and a weak additional maximum appeared between them. The observations indicated that the vacancy exhibited a partially occupied, and at least one empty, localized defect state. The results well supported electronic structure calculations.

Electronic properties of the Ga vacancy in GaP(110) surfaces P.Ebert, K.Urban: Physical Review B, 1998, 58[3], 1401-4