Effects of spontaneous ordering on Raman spectra of GaInP2

The effects of spontaneous CuPtB ordering on the lattice dynamics of GaInP2 allays are studied by room-temperature Raman-scattering experiments on a series of GaInP2 samples with various degrees of ordering, grown by organometallic vapor phase epitaxy. In measurements on the (001) growth plane, we have observed several changes in the optical-phonon range of the Raman spectrum, the most notable of which is the emergence of an extra peak at 354 cm(-1). This peak is identified as a longitudinal-optical mode due to the superlattice effect In the ordered alloys. The acoustic-phonon range of the (001) Raman spectra of the ordered samples shows extra peaks at 60 and 205 cm(-1), which are identified as the folded transverse and longitudinal acoustic phonons, respectively. For the optical phonons, the Raman selection rules and the identification of the extra peak are tested by measuring right-angle Raman scattering. The results are consistent with the trigonal C-3v symmetry of the ordered alloys.