X-RAY ABSORPTION FINE STRUCTURE SPECTROSCOPY OF THIN FILM SiGe ALLOYS

Abstract

<p>SiGe thin film alloys are the subject of intense interest in semiconductor research. The extent of bond length dependence upon alloy composition in these materials is a subject of some debate in the literature. This work details our Si and Ge K-edge extended x-ray absorption fine structure (EXAFS) measurements on a selection of strained and relaxed single crystal SiGe alloys. Constrained, simultaneous fits to the EXAFS of multiple spectra from both Si and Ge K-edges were performed in order to extract quantitative data for bond lengths and co-ordination numbers.</p> <p>The first analysis was performed solely using EXAFS spectra from relaxed alloys grown on Si. The results indicate that first shell bonding in relaxed SiGe alloys adheres to a weakly mixed Pauling-Vegard regime, showing detectable composition dependence (bond length change of 0.03 A over the full composition range). In the</p> <p>notation of the CT theory of Thorpe and co-workers <em>(Phys. Rev. </em>B 46,15872 (1992)), the topological rigidity parameter, a** is found to be 0.70+0.09 -0.03</p> <p>The results are compared to other theoretical and experimental results, and alternate models to the CT theory are explored. Ordering effects in the co-ordination numbers are also evaluated.</p> <p>The second analysis was performed on a small range of complimentary strained and relaxed samples, to investigate the hypothesis that strained SiGe alloys on Si(100) have shorter bond lengths than relaxed samples. The results of the analysis suggest that strain accommodation is at least partly accomplished by bond length contraction.</p> <p>Finally, the Appendix details a complimentary project in near-edge x-ray absorption fine structure measurements of SiGe alloys. Specifically, a strain-induced polarisation dependence in the Si K-edge spectra of SiGe films is explored with measurements of a large range of samples. The results indicate that the source of the polarisation is not yet fully understood.</p>