SI K-EDGE AND GE K-EDGE X-RAY-ABSORPTION SPECTROSCOPY OF THE SI-GE INTERFACE IN [(SI)M(GE)N]P ATOMIC LAYER SUPERLATTICES

The sensitivity of X-ray absorption near edge (XANES) spectra to the s tructure around the core excited atom has been explored by comparisons of the Si K-edge and Ge K-edge spectra of SiMe4, Ge(SiMe3)4, Si(GeMe3 )4, Si(SiMe3)4, Ge(Me)4 and Ge2(Me)6 molecular compounds (Me = methyl) ; single crystal and amorphous Si; single crystal Ge; single crystal S i1-xGex alloys, and [(Si)m(Ge)n]p atomic layer superlattices grown by molecular beam epitaxy. Systematic changes with changing environment a re detected. The spectral trends as well as comparison with spherical wave multiple scattering calculations of variable size Si(Si)nunderbar and Si(Ge)nunderbar clusters (4 < n < 190), indicate that many aspect s of the near edge (0-50 eV) spectral features in the semiconductors a re determined by structure far beyond the first coordination shell and that there are strong multiple scattering contributions. Two maxima s eparated by 0.80(3) eV are found as the lowest energy features in the Si K-edge spectrum of crystalline Si. These are attributed to 1s --> 3 p conduction band (CB) excitations. Even larger splittings are observe d in the corresponding 1s --> CB structure in CTe-rich Si1-xGex alloys and the atomic layer superlattice samples. The CB splitting varies sy stematically with the superlattice structure. The utility of the vario us components of the XANES signal for characterizing the Si-Ge interfa ce in [(Si)m(Ge)n]p superlattice samples is discussed.