Abstract

MARIN, Giovanni et al. Urbach´s tail in the ordered vacancy compound CuGa₃Te₅. Rev. Téc. Ing. Univ. Zulia [online]. 2009, vol.32, n.1, pp.55-59. ISSN 0254-0770.

The optical absorption coefficient just below the absorption edge varies exponentially with the energy of incident photon, indicating the presence of Urbach’s tail. The phonon energy hn_p associated with Urbach’s tail, which in the average is found to be 50 meV, is higher than the highest optical phonon mode that would be expected from in Raman spectroscopy, which is about 27 meV. The origin of the additional energy is attributed to the contribution of localized modes produced by structural disorder of low energy formation as the Donor-Acceptor defects Pair DADP`s. An empirical relation, also used earlier in the case of 1:1:2 and other ordered defect compounds of the 1:3:5 phases, explains very well the variation of Urbach’s energy with temperature.

Keywords : Ordered vacancy compound; Urbach tail; average phonon energy.