SUPERLATTICE EFFECTS INDUCED BY ATOMIC ORDERING ON GAXIN1-XP RAMAN MODES

A polarized Raman scattering study is undertaken in order to investiga te the atomic ordering in (001)-oriented Ga0.51In0.49P layers lattice matched to GaAs and preliminarily characterized by photoluminescence. The superlattice structure of trigonal symmetry which results from ord ering manifests itself through phonon mode modifications. Several new modes are detected and their frequency and intensity behaviors are pro perly analyzed. In addition to the folded longitudinal-acoustic mode o n Raman spectra, we observed the folded transverse-acoustic mode. Both folded acoustic modes display narrow lines (similar to 10 cm(-1)) sup erposed to the disorder-induced acoustic bands DALA and DATA of the al loy. In the ''optical mode'' frequency range one clearly observes a do ubling of the longitudinal GaP-type and InP-type modes, never reported before to our knowledge. The magnitude of the splitting between the t wo components of the LO doublet is measured precisely in the case of G aP-type modes and is an increasing function of the atomic ordering deg ree. So it is with intensities of the TO modes which become Raman acti ve due to the trigonal symmetry. Finally the ''valley depth'' which ha d been empirically assigned as a significant parameter of the atomic o rdering degree, is now precisely interpreted in the light of the whole Raman study.