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Defect-induced increase in the phonon energy involved in the formation of Urbach tail in Cu-ternaries
Authors:SM Wasim  I Bonalde  G Marín
Institution:a Centro de Estudios de Semiconductores, Facultad de Ciencias, Universidad de los Andes, Mérida 5101, Venezuela
b Centro de Física, Instituto Venezolano de Investigaciones Científicas, Apartado 21874, Caracas 1020-A, Venezuela
Abstract:From a combined analysis of the stoichiometric composition and Urbach tail in samples of CuInSe2, CuInTe2, and CuGaTe2 of the I-III-VI2 family of chalcopyrite semiconductors, it is found that the energy p involved in the electron/exciton-phonon interaction is a linear function of a parameter Δz which is the sum of the deviations from ideal molecularity Δx and anion to cation ratio Δy. It gives evidence that in the copper ternaries p is associated to the structural defects caused by cation-cation, cation-anion, and other intrinsic disorders. The high value of p found in the studied samples, higher than the highest optical mode, is shown to come from the contribution of the additional phonon energy due to structural defects. This is in agreement with recently proposed models of the temperature dependence of the Urbach energy.
Keywords:A  Semiconductors  A  Electronic materials  D  Defects  D  Optical properties  D  Lattice dynamics
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