Luminescent FeSi2 crystal structures induced by heteroepitaxial stress on Si(111)

The crystal structures and the luminescent properties of FeSi2 in the FeSi2/Si heteroepitaxial system have been investigated by first principles calculations. The results indicate that the heteroepitaxial beta -FeSi2 facing Si(111) by the (110) plane will be deformed from an orthorhombic to a monoclinic P2(1)/c structure with a gamma angle of 95 degrees. 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 -FeSi2, we propose the strained FeSi2(110)/Si(111) structure to be the origin of the luminescence observed in the FeSi2/Si systems.