  InAs_{x}Sb_{1-x} alloys show a strong bowing in the energy gap, the energy
gap of the alloy can be less than the gap of the two parent compounds. We
demonstrate that a consequence of this alloying is a systematic degradation in
the sharpness of the absorption edge. The alloy disorder induced band-tail
(Urbach tail) characteristics are quantitatively studied for
InAs_{0.05}Sb_{0.95}.
