DIRECT PHOTON-PHONON COUPLING AT (001) SURFACES OF ZINCBLENDE STRUCTURE CRYSTALS

The loss of translational symmetry at solid surfaces relaxes the momen tum conservation constraints in photon-phonon coupling processes. We s tudy this coupling at polar crystal surfaces and its manifestation in far-infrared reflection anisotropy spectra (RAS). We apply the Keating valence force potential to describe short-range mechanical interactio ns together with long-range Coulomb forces and radiation fields, and w e solve analytically the ensuing system of coupled equations for the e lectromagnetic held and the lattice vibrations. We calculate the far-i nfrared normal reflectance spectra of (001) surfaces of semi-infinite zinc-blende crystals. They display a resonance structure associated wi th the excitation of surface and bulk phonon modes which might be obse rved with far-infrared RAS. (C) 1998 Elsevier Science B.V. All rights reserved.