The crystal structures and the luminescent properties of $\mathrm{FeSi}{}_2$ in the $\mathrm{FeSi}{}_2/\mathrm{Si}$ heteroepitaxial system have been investigated by first principles calculations. The results indicate that the heteroepitaxial $\beta -\mathrm{FeSi}{}_2$ facing Si(111) by the (110) plane will be deformed from an orthorhombic to a monoclinic ${P2\mathrm{}}_1/c$ structure with a $\gamma$ angle of $95°$. The strained crystal has a direct gap band structure and a finite oscillator strength of 0.7 between the band edges at the $Y$ point. Since an indirect type band structure is obtained for other heteroepitaxial relationships, as well as for the bulk $\beta -\mathrm{FeSi}{}_2$, we propose the strained $\mathrm{FeSi}{}_2\left(110\right)/\mathrm{Si}\left(111\right)$ structure to be the origin of the luminescence observed in the $\mathrm{FeSi}{}_2/\mathrm{Si}$ systems.

• Received 25 August 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.6006