Nonresonant Faraday rotation in glassy semiconductors

Nonresonant interband Faraday rotation in amorphous semiconductors, as a function of photon energy, may be described by an equation derived for direct transitions in crystalline semiconductors. In this paper it is shown how this equation may be obtained for the former case also, assuming a parabolic density of states function N(E) and a correlation between valence- and conduction-band states. The analysis of experiments on chalcogenide glasses reveals a Faraday-rotation energy gap EgFR that is significantly larger than the optical gap Egᵒᵖᵗ. The effect is attributed to transitions between extended states, so that it is meaningful to compare EgFR with the mobility gap Eg^μ. For oxide glasses both gaps are comparable but for chalcogenide glasses EgFR is too large by a few tenths of 1 eV.