STRUCTURE AND ELECTRONIC-PROPERTIES OF FESI2

The nature of the band gap in the semiconducting material beta-FeSi2 i s still under some dispute. Although most experimental results indicat e the band gap to be direct, nb initio work generally reports the mate rial to be an indirect semiconductor with the direct transition a few tens of millielectron volts higher than the indirect gap. However, bet a-FeSi2 is commonly grown epitaxially on a diamond-structure Si substr ate, and as a consequence, the beta-FeSi2 unit cell is strained. Here we report the results of ab initio density-functional calculations, wh ich we have performed on beta-FeSi2 where its lattice parameters are c onstrained according to the heteroepitaxial system beta-FeSi2(100)/Si( 001). This forms two types of lattice matching: (A) beta-FeSi2[010] pa rallel to Si (110)and (B) beta-FeSi2[010] parallel to Si(001). We find that the beta-FeSi2 band gap is highly sensitive to its lattice param eters and therefore to the orientation at which the material is grown on silicon. We find that type A favors a more direct band gap, while t ype B has an indirect gap. [S0163-1829(98)05039-5].