The Raman spectra of GaAs and InP implanted with Be ions with fluences ranging from 5 X 10 12 to I X 10 16 cm -2 were investigated. A marked difference in the behavior of the TO and La modes with respect to broadening with fluence was observed and the results indicate that this is caused by frequency dependent anharmonic damping constants. The Raman spectra of high fluence samples are interpreted in terms of disorder-induced first-order Raman spectra due to phonons with nonzero wave vectors. The similarities between our "Reduced Raman Spectra" of the disordered form and the theoretical one-phonon density of states, are presented without introducing Gaussian broadening as suggested by earlier authors studying amorphous materials. The observations support the conclusion that the form essentially retains the short-range order of the crystalline phase; the phonon spectrum of the crystal is largely determined only by nearneighbor interactions; and the existence of a frequency-dependent coupling constant for the scattering intensity at least in the low frequency region.

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