PHONON MODES IN SPONTANEOUSLY ORDERED GAINP2 STUDIED BY MICRO-RAMAN SCATTERING MEASUREMENTS

We have performed micro-Raman-scattering experiments on ordered GaInP2 alloy samples in three different geometries where the phonon wave vec tor is either parallel or perpendicular to the ordering axis of the cr ystal. By comparing results from the ((1) over bar 11) backscattering and right-angle scattering measurements with the C-3v symmetry of the crystal, we found that the recently discovered peaks at 205 and 354 cm (-1) in the Raman spectra of ordered alloys are due to longitudinal-ph onon modes with A(1) symmetry in these geometries. In the (110) backsc attering geometry, selection-rule forbidden Longitudinal-phonon modes appear in the Raman spectra measured in parallel polarizations. Possib le mechanisms for this selection-rule violation are discussed.