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