The local lattice distortion relating to the phosphorus antisite defect (PGa) in the P+‐ion‐implanted GaP layer was studied using Rutherford backscattering (RBS), photoacoustic (PA), Raman scattering, and photoluminescence (PL) methods. The displacement fraction due to the excess phosphorus in 800 °C annealed samples is estimated to be ∼2×1020/cm3by RBS channeling measurements. The slight reduction of the LO‐TO phonon frequency splitting of the annealed P+‐ion‐implanted GaP with respect to the unimplanted one indicates the presence of PGa, corresponding tox=0.0084 of Ga1−xP1+x. This is consistent with the displacement fraction estimated by RBS. A PL emission relating to PGais observed at 716 mm (1.73 eV). ©1995 American Institute of Physics.