Infrared and Raman studies of confined and interface optical phonons in short-period GaAs/AlAs superlattices with a grating coupler

The optical phonon modes in short-period GaAs/AlAs superlattices were inves tigated by means of Raman spectroscopy and far-infrared reflection spectros copy using a grating coupler technique. Grating couplers provide a wave vec tor transfer parallel to the layers, enabling study of in-plane dispersion of the phonon modes in the superlattice structure. The mixing of confined a nd interface optical modes was observed as the in-plane phonon wave vector was varied. The experimental frequencies of the superlattice optical modes obtained from infrared and Raman spectra are in good agreement with calcula tions performed using a dielectric continuum model. (C) 1999 American Vacuu m Society. [S0734-211X(99)07204-2].