Raman Study of the Anomalous TO Phonon Structure in GaP with Controlled Isotopic Composition

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Abstract
The transverse optical (TO) phonon in GaP has been measured in crystals with varying Ga isotopic composition by means of Raman scattering. In high resolution experiments at low temperature, we find a striking double peak structure in the line shape of natural GaP which varies with the Ga isotope abundance in a systematic manner. We calculate the spectra assuming anharmonic interaction of the TO phonon with a band of acoustic modes given by a model two-phonon density of states. This approach explains the measured Raman profiles and the isotope effects.