Phonon localization in ion-irradiated GaAs

Real-time Raman measurements have been carried out on GaAs (100) surface under 5 keV He+ irradiation. Lattice disordering induced by ion irradiation has been investigated in terms of phonon correlation length, which is obtained from the Raman spectral line shape of the longitudinal optical phonon. The phonon correlation length decreases inversely proportional to the cubic root of the ion fluence. The result has been compared with the previous work on graphite, where the phonon correlation length was inversely proportional to the square root of the ion fluence. It is shown that the phonon becomes localized due to defect formation by ion irradiation, and the phonon correlation length corresponds linearly to the mean distance of the defects in GaAs.