STRUCTURAL-PROPERTIES OF ION-BEAM-SYNTHESIZED BETA-FESI2 IN SI(111)

A continuous buried beta-FeSi2 layer was obtained by implantation of 200 keV Fe+ ions into Si(111) wafers at elevated temperature. During the subsequent rapid thermal annealing at 1150-degrees-C for 10-s, a continuous buried layer of the metallic alpha-FeSi2 phase is formed. During the second annealing step at 800-degrees-C, the alpha-phase is completely transformed into the semiconducting beta-phase. The epitaxial relationship between the beta-FeSi2 and the silicon substrate was investigated by transmission electron microscopy. It was found that the beta-FeSi2(010) plane grows parallel to the Si(111) substrate. Two different azimuthal orientations were observed. For the first azimuthal orientation, the beta-FeSi2[001] direction is oriented almost parallel to one of the three Si<110> directions lying in the interface. In the second azimuthal orientation, the beta-FeSi2[100] direction lies parallel to one of the Si<110> directions in the interface. The lattice parameter mismatch and the growth mechanism must be considered to be the main reasons for the epitaxial relationship of the Si(111)/beta-FeSi2/Si(111) heterostructures studied in this alpha-phase which is formed during the first annealing step. Different orientation relationships were observed for beta-FeSi2 prepared by solid phase epitaxy and ion beam synthesis without high-temperature annealing.