Effects of Spontaneous Ordering on Raman Spectra of GaInP2

The effects of spontaneous CuPtB ordering on the lattice dynamics of GaInP2 alloys 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 ofwhich 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 C3v symmetry of the ordered alloys.