Si/Fe flux ratio influence on growth and physical properties of polycrystalline β-FeSi2 thin films on Si(100) surface

Abstract

This work investigates the Si/Fe flux ratio (2 and 0.34) influence on growth of β-FeSi2 polycrystalline thin films on Si(100) substrate at 630 ˚C. Lattice deformation for the films obtained are confirmed by X-ray diffraction analysis (XRD). The volume unit cell deviation from that of β-FeSi2 single crystal are 1.99 % and 1.1 % for Si/Fe = 2 and Si/Fe = 0.34, respectively. Absorption measurements show that the indirect transition (~ 0.813 eV) of the Si/Fe = 2 sample changes to the direct transition with a bandgap value of ~0.806 eV for the sample prepared at Si/Fe = 0.34. Along with this direct transition, the absorption spectra exhibit an additional feature with an excitation energy of ~0.56 eV. Surface magneto-optic Kerr effect (SMOKE) measurements detect ferromagnetic behavior of the β-FeSi2 polycrystalline films grown at Si/Fe = 0.34 at T=10 K, but no ferromagnetism was observed in the samples grown at Si/Fe = 2. Theoretical calculations refute that the cell deformation can cause the emergence of magnetization and argue that the origin of the ferromagnetism, as well as the lower impurity direct transition, is β-FeSi2 stoichiometry deviations. Raman spectroscopy measurements evidence that the film obtained at Si/Fe flux ratio equal to 0.34 has the better crystallinity than the Si/Fe = 2 sample