EFFECT OF MULTIPLE-STEP ANNEALING ON THE FORMATION OF SEMICONDUCTING BETA-FESI2 AND METALLIC ALPHA-FE2SI5 ON SI(100) BY ION-BEAM SYNTHESIS

Polycrystalline semiconducting beta-FeSi2 layers on Si (100) have been formed by ion beam synthesis. Results from two different annealing pr ocesses, either two-step (2SA) annealing up to 900 degrees C or three- step annealing (3SA) up to 1100 degrees C, are discussed. beta-FeSi2 g rown by 3SA has shown a typical direct band-gap energy (E-gdir) of 0.8 8 eV and a high localized defect density (N-0) of 1.0 x 10(18) cm(-3), the latter being due to crystallographic mismatches or relevant defec ts at grain boundaries introduced during the transformation process fr om beta to alpha. On the contrary, beta-FeSi2 grown by 2 SA has shown a lower E-g(dir) of 0.80eV and a smaller N-0 of 1.7 x 10(17) cm(-3), t he former arising from a deviation of the stoichiometric composition t o the Si-rich side. Broad PL bands near 0.8eV have been observed at 2K from both 2SA and 3SA samples, and we assign these PL bands to optica l radiative transitions intrinsic to beta-FeSi2.