The optical properties of beta-FeSi2 fabricated by ion beam assisted sputtering

beta-FeSi2 has been shown to have a minimum direct band gap of 0.87 eV [T.D . Hunt, K.J. Reeson, K.P. Homewood S.W. Teen, R.M. Gwilliam, B.J. Sealy, Nu cl. Instr. and Meth. B 84 (1994) 168-171] which leads to the opportunity fo r Si based opto-electronics, optical communications and optical interconnec ts. Electroluminescence has been reported From structures containing beta-F eSi2, which were produced by high dose ion implantation and annealing [D. L eong, M.A. Harry, K.J. Reeson, K.P. Homewood. Nature 387 (12 June 1987) 686 ]. In this paper we report the formation of beta-FeSi2 by ion beam assisted co-sputtering of Fe and Si in varying percentages. The layers were deposited with a varying Fe/Si ratio, with a Si capping lay er applied to prevent oxidation. Separate regions of the sample were invest igated at room temperature using optical absorption, to measure the band ga p values. Absorption under the fundamental edge was also analysed at room t emperature. Further investigations looked at the temperature dependence of the band gap and the absorption tinder the fundamental edge. The results showed that a variety of Fe/Si ratios produced beta-FeSi2, the formation of which was ascertained by the presence of a suitable band gap v alue [0.83-0.88 eV]. Absorption under the fundamental edge was shown to fol low an exponential Urbach tail [C.H. Grein. S. John, Phys. Rev. B 39 (1989) 1140]. The temperature measurements are in good agreement with the Einstei n model. (C) 2000 Elsevier Science B.V. All rights reserved.