Ion-beam synthesized polycrystalline semiconducting FeSi2 on Si(001) was investigated by means of transmission measurements at temperatures of between 10 and 300K. The existence of a minimum direct band-gap was demonstrated, and its variation with temperature was analyzed in terms of a 3-parameter thermodynamic model and the Einstein model. The band-tail states, and states on a shallow impurity level, were found to give rise to absorption below the fundamental edge. The existence of an Urbach exponential edge was demonstrated, and the temperature dependence of the Urbach tail-width was studied on the basis of the Einstein model. A strong structural disorder that was associated with grain boundaries between, and within, FeSi2 grains (and their related defects) was found to be the predominant contribution at room temperature.

Z.Yang, K.P.Homewood, M.S.Finney, M.A.Harry, K.J.Reeson: Journal of Applied Physics, 1995, 78[3], 1958-63