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 re flectivity (SDR) data. The analysis of SDR data is done in the framewo rk of a macroscopic three-layer model in which the media involved (vac uum, 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 rang e explored. From the experimental data SDF has been computed for light electric vector along [1(1) over bar0$] and [001] directions, i.e., p arallel 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 t hey differ markedly because of the effect of bulk contribution. Three mainly isotropic structures are clearly visible in the deconvolved eps ilon'' spectra at the following photon energies: 2.7, 3.3, and 3.7 eV. Such structures are interpreted in terms of optical transitions betwe en surface state bands as derived from direct and inverse photoemissio n. The transition at 2.7 eV is assigned at the Gamma point in the surf ace 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 u p to 4.0 eV resulting in slightly more than 0.5. (C) 1995 American Vac uum Society.