SURFACE ELECTRON-DIFFRACTION PATTERNS OF BETA-FESI2 FILMS EPITAXIALLY GROWN ON SILICON

Semiconducting beta-FeSi2 is drawing much current research interest because of hoped-for silicon-based optoelectronics applications. The study of heteroepitaxial film growth on silicon depends heavily upon several transmission and reflection electron-diffraction techniques. Because of the complicated crystal structure of this material, the possibility of competing heteroepitaxial relationships, the propensity for formation of epitaxial variants by rotation twinning, and the uncertainty in the crystalline surface nets, the analysis of experimental diffraction patterns is complicated. A theoretical reference for a number of fundamental electron-diffraction patterns is provided and they are illustrated with a broad range of experimentally obtained patterns from the surfaces of epitaxial films. In situ transmission reflection high-energy electron diffraction (RHEED) (transmission electron diffraction with conventional RHEED instrumentation), from rough but epitaxial films, is of great utility and quite feasible with epitaxial systems such as this one, which exhibit a tendency toward islanding. The possibilities for experimentally distinguishing, with this technique, the competing epitaxial relationships on Si(111) are clarified; it is found that the beta-FeSi2 (110) matching face is certainly present in these samples and the (101) may be also. An experimental determination of the two-dimensional space groups of the (100), (110), and (101) faces is also presented-in the first and third cases the surface unit meshes are different from the simple projections of the bulk crystalline unit cell.