POLARIZATION DEPENDENCE OF THE SIK-EDGE X-RAY-ABSORPTION SPECTRA OF SI-GE ATOMIC LAYER SUPERLATTICES

The polarization dependence of the SiK-edge X-ray absorption spectra o f several [(Si)(m)(Ge)(n)](p) atomic layer superlattice (ALS) material s grown on both Si(100) and Ge(100) have been investigated using plane polarized synchrotron radiation. These spectra exhibit sharp, polariz ation dependent, Si 1s --> conduction band (CB) resonance features whi ch are absent in the spectrum of amorphous Si (a-Si). Subtraction of t he spectrum of a-Si from that of the crystalline ALS materials is used to isolate the conduction band structure. A constrained curve fit ana lysis of up to eight data files simultaneously has been used to quanti tatively analyze the signal. The CB structure is composed of number of polarization independent components and several polarization dependen t components. In [(Si)(2)(Ge)(6)](40)/Ge(100) the lowest energy transi tion at 1839.1 eV is polarized along the surface normal (the growth di rection) while a doublet structure centred at 1841 eV is polarized in the surface plane (perpendicular to the growth direction). A similar s pectral pattern is found in [(Si)(6)(Ge)(2)](48)/Si(100) but the polar ization effect is weaker and the sense of the polarization effect is r eversed. The polarization dependent signal is attributed to anisotropi c states associated with strain-induced tetragonal distortions in the strained-ALS materials.