Far-Infrared dielectric anisotropy and phonon modes in spontaneously CuPt-ordered Ga0.52In0.48P -: art. no. 195204

The phonon properties of partially CuPtB-ordered Ga0.52In0.48P with degrees of ordering eta=0,0.19,0.28,0.35,0.47, determined from generalized ellipsometry measurement of the near-band-gap order birefringence, are studied by far-infrared spectroscopic ellipsometry. We determine precise spectra of the anisotropic dielectric functions. With increasing eta all Ga0.52In0.48P phonon modes split in E- and A(1)-type vibrations with polarization perpendicular and parallel to the sublattice ordering direction, respectively, and the mode frequencies shift continuously. We demonstrate here that the alloy-induced modes previously observed in highly disordered Ga0.52In0.48P [Phys. Rev. B 64, 155206 (2001)] have their origin in the ordered atomic arrangement of alike group-III atoms. We propose far-infrared dielectric anisotropy as a sensitive measure for sublattice ordering in multinary III-V alloys.