Surface Science 301 (1994) 260-272

Polarization dependence of the Si K-edge X-ray absorption
spectra of Si-Ge atomic layer superlattices

A.P. Hitchcock*, T. Tyliszczak, P. Aebi 1
Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L8S 4M1
X.H. Feng
CSRF, SRC, University of Wisconsin-Madison, Stoughton, WI, USA
Z.H. Lu, J.-M. Baribeau, T.E. Jackman
Institute for Microstructural Sciences, National Research Council, Ottawa, Canada

(Received 7 May 1993; accepted for publication 19 August 1993)

The polarization dependence of the SiK-edge X-ray absorption spectra of several [(Si)m(Ge)n]p atomic layer superlattice (ALS) materials grown on both Si(100) and Ge(100) have been investigated using plane polarized synchrotron radiation. These spectra exhibit sharp, polarization dependent, Si ls® conduction band (CB) resonance features which are absent in the spectrum of amorphous Si (a-Si). Subtraction of the spectrum of a-Si from that of the crystalline ALS materials is used to isolate the conduction band structure. A constrained curve fit analysis of up to eight data files simultaneously has been used to quantitatively analyze the signal. The CB structure is composed of a number of polarization independent components and several polarization dependent components. In [(Si)2 (Ge)6]40/Ge(100) the lowest energy transition at 1839.1 eV is polarized along the surface normal (the growth direction) while a doublet structure centred at 1841 eV is polarized in the surface plane (perpendicular to the growth direction). A similar spectral pattern is found in [(Si)6(Ge)2]48/Si(100) but the polarization effect is weaker and the sense of the polarization effect is reversed. The polarization dependent signal is attributed to anisotropic states associated with strain-induced tetragonal distortions in the strained-ALS materials.

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