Raman scattering and infrared reflectivity in [(InP)(5)(In0.49Ga0.51As)(8)](30) superlattices

We have measured far-infrared and infrared reflectivity as well as Raman sc attering in an [(InP)(5)(In0.49Ga0.51As)(8)](30) superlattice grown by mole cular beam epitaxy. A numerical model for calculating the reflectivity coef ficient for complex systems which includes superlattice, buffer layer, and substrate has been developed. The far-infrared reflectivity spectra consist s of the superlattice confined and interface modes as well as the modes fro m the buffer layer (In0.49Ga0.51As) and the substrate (InP). In the infrare d spectral range above 1000 cm(-1) we observe only interference fringes fro m the buffer layer. A good agreement between calculated and experimental sp ectra is achieved. The folded longitudinal acoustic phonon doublet appears at about 39 cm(-1) in the Raman scattering spectra. The frequency agrees we ll with a continuum model calculation. In the optical phonon spectral regio n we observe confined modes corresponding to both constituents. The modes r epresenting vibrations of atoms at both interfaces: InP/InGaAs (230 cm(-1) mode) and InGaAs/InP (240 and 260 cm(-1) modes) have also been observed. Th e geometrical parameters of the sample, obtained from the fitting of the re flectivity data, agree well to the values of the layer thickness obtained b y double crystal x-ray diffraction. (C) 2000 American Institute of Physics. [S0021-8979(00)01017-3].