SURFACE ELECTRON-DIFFRACTION PATTERNS OF BETA-FESI2 FILMS EPITAXIALLYGROWN ON SILICON

Semiconducting beta-FeSi2 is drawing much current research interest be cause of hoped-for silicon-based optoelectronics applications. The stu dy of heteroepitaxial film growth on silicon depends heavily upon seve ral transmission and reflection electron-diffraction techniques. Becau se of the complicated crystal structure of this material, the possibil ity of competing heteroepitaxial relationships, the propensity for for mation of epitaxial variants by rotation twinning, and the uncertainty in the crystalline surface nets, the analysis of experimental diffrac tion patterns is complicated. A theoretical reference for a number of fundamental electron-diffraction patterns is provided and they are ill ustrated with a broad range of experimentally obtained patterns from t he surfaces of epitaxial films. In situ transmission reflection high-e nergy electron diffraction (RHEED) (transmission electron diffraction with conventional RHEED instrumentation), from rough but epitaxial fil ms, is of great utility and quite feasible with epitaxial systems such as this one, which exhibit a tendency toward islanding. The possibili ties for experimentally distinguishing, with this technique, the compe ting epitaxial relationships on Si(111) are clarified; it is found tha t the beta-FeSi2 (110) matching face is certainly present in these sam ples and the (101) may be also. An experimental determination of the t wo-dimensional space groups of the (100), (110), and (101) faces is al so presented-in the first and third cases the surface unit meshes are different from the simple projections of the bulk crystalline unit cel l.