Exciton absorption in beta-FeSi2 epitaxial films

Experimental evidence is given for excitonic transitions in semiconducting iron disilicide. Epitaxial films of beta-FeSi2 on Si(100) were studied by o ptical transmission and reflection measurements at 10 K and at room tempera ture as well as room temperature spectral ellipsometry. Two sharp peaks wer e found in the low temperature spectra, which can be ascribed to the ground state and the first excited state of excitons. Assuming free Wannier-Mott excitons, a value of 16 meV is obtained for the binding energy. A value of 0.93 eV for the ionization energy results with this assumption. This coinci des with the value of the direct energy gap determined at 10 K. Compared to room temperature the energy gap is blue shifted by 40 meV. (C) 1999 Americ an Institute of Physics. [S0003-6951(99)00907-9].