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

Abstract

The sensitivity of X-ray absorption near edge (XANES) spectra to the structure around the core excited atom has been explored by comparisons of the Si K-edge and Ge K-edge spectra of SiMe 4, Ge(SiMe 3) 4, Si(GeMe 3) 4, Si(SiMe 3) 4, Ge(Me) 4 an Ge 2(Me) 6 molecular compounds (Me = methyl); single crystal and amorphous Si; single crystal Ge; single crystal Si 1− x Ge x alloy and [( Si) m ( Ge) n ] p atomic layer superlattices grown by molecular beam epitaxy. Systematic changes with changing environment are detected. The spectral trends as well as comparison with spherical wave multiple scattering calculations of variable size Si(Si) n and Si(Ge) n clusters (4 < n < 190), indicate that many aspects of the near edge (0–50 eV) spectral features in the semiconductors determined by structure far beyond the first coordination shell and that there are strong multiple scattering contributions. Two maxima separated 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 → 3p conduction band (CB) excitations. Even larger splittings are observed in the corresponding 1s → CB structure in Ge- rich Si 1− x Ge x alloys and the atomic layer superlattice samples. The CB splitting varies systematically with the superlattice structure. The utility of the various components of the XANES signal for characterizing the SiGe interface in [( Si) m ( Ge) n ] p superlattice samples is discussed.