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].