Far-Infrared dielectric anisotropy and phonon modes in spontaneously CuPt-orderedGa0.52In0.48P

Abstract

The phonon properties of partially ${\mathrm{CuPt}}_{B}$-ordered ${\mathrm{Ga}}_{0.52}{\mathrm{In}}_{0.48}\mathrm{P}$ with degrees of ordering $\ensuremath{\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 $\ensuremath{\eta}$ all ${\mathrm{Ga}}_{0.52}{\mathrm{In}}_{0.48}\mathrm{P}$ 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 ${\mathrm{Ga}}_{0.52}{\mathrm{In}}_{0.48}\mathrm{P}$ [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.