SURFACE DIELECTRIC FUNCTION OF CDTE(110) OBTAINED BY POLARIZED SURFACE DIFFERENTIAL REFLECTIVITY DATA

We present a determination of the complex surface dielectric function (SDF) of CdTe(110) obtained by using polarized surface differential reflectivity (SDR) data. The analysis of SDR data is done in the framework of a macroscopic three-layer model in which the media involved (vacuum, surface, and substrate) are assumed to have definite anisotropic functions. A relation between SDR data and the complex SDF is obtained under the assumption that the oxide layer is nonabsorbing in the range explored. From the experimental data SDF has been computed for light electric vector along [1(1) over bar0$] and [001] directions, i.e., parallel and perpendicular to the natural chains of the unreconstructed (110) surface. In the energy range below 3.3 eV the imaginary part of SDF (epsilon(s)'') and SDR data are very similar while above 3.3 eV they differ markedly because of the effect of bulk contribution. Three mainly isotropic structures are clearly visible in the deconvolved epsilon'' spectra at the following photon energies: 2.7, 3.3, and 3.7 eV. Such structures are interpreted in terms of optical transitions between surface state bands as derived from direct and inverse photoemission. The transition at 2.7 eV is assigned at the Gamma point in the surface Brillouin zone, the one at 3.3 eV at the Gamma and X while the one at 3.7 eV at the X and X'. The effective number of electrons per atom participating in the optical transitions is calculated for energies up to 4.0 eV resulting in slightly more than 0.5. (C) 1995 American Vacuum Society