Redshift of the longitudinal optical phonon in neutron irradiated GaP

Redshift of the longitudinal optical (LO) phonon relating to the defect structure in neutron-irradiated GaP has been studied using Raman scattering, electron paramagnetic resonance, x-ray diffraction, and Fourier-transform infrared absorption methods. The defect structure is discussed for the two cases of vacancy-interstitials and antisites using a simple model of the LO-transverse optical phonon frequency splitting (Delta omega). It is suggested that the slight reduction of Delta omega originates from the vacancy-interstitial clusters rather than the antisite defects, considering the annealing behavior of the antisite defect concentrations, the volume expansion, and infrared absorption in neutron-irradiated samples. The clusters are associated with a volume expansion of about 0.13% observed in the neutron-irradiated samples. (C) 1999 American Institute of Physics. [S0021-8979(99)05407-9].