Phonon modes of [111] GaP/InP monolayer superlattices in Raman spectra of spontaneously ordered GaInP

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Abstract
It has been established that backscattering diagonal polarization of Raman spectra (RS) of alloys, grown by metalorganic vapour phase epitaxy on [001] GaAs substrates, has strong anisotropy in {110} directions, owing to partial ordering into a and GaP/InP monolayer superlattice (MSL) structure (-type structure). Using RS polarization anisotropy, the frequencies of [001]-wavevector phonons polarized parallel and perpendicular to mirror planes of {111} GaP/InP MSL have been measured. The results of lattice-dynamical calculation for the {111} GaP/InP MSL on the basis of the shell model, using bulk parameters for both the constituents, are presented. When the Ga - P and In - P bond lengths remain unchanged, the model predicts trigonal stretching of the MSL unit cell relative to that of the zinc-blende structure. High sensitivity of RS and their polarization anisotropy to the microstructure of spontaneously ordered has been demonstrated.