ELECTRONIC-STRUCTURE OF BURIED ALPHA-FESI2 AND BETA-FESI2 LAYERS - SOFT-X-RAY EMISSION AND ABSORPTION STUDIES COMPARED TO BAND-STRUCTURE CALCULATIONS

The electronic structure of buried -FeSi2 and -FeSi2 layers produced by ion-beam synthesis has been studied. Using fluorescence spectroscopies, we were able to investigate the silicide layers, which are buried below a 600- Si cap layer, in situ. The occupied local Fe d density of states was determined by Fe L3 soft-x-ray-emission spectra, excited both with high-energy electrons and monochromatized synchrotron radiation. Using soft-x-ray-absorption spectra recorded in the fluorescence-yield mode at the same Fe L3 edge, the unoccupied Fe d density of states was determined. The formation of a band gap of 0.80.2 eV in the electronic states of d symmetry at the Fe atoms of -FeSi2 could be observed in the experiments. We present ab initio band-structure calculations for -FeSi2 and -FeSi2 and compare the results to the spectroscopic data. The influence of a core hole on the soft-x-ray-absorption spectrum is studied by calculating the electronic structure of a substitutional impurity in the form of a core 2p3/2 ionized Fe atom using a supercell calculation. © 1994 The American Physical Society.