Polymorphism in CuInS2 epilayers:: Origin of additional Raman modes

CuInS2 epitaxial films grown on Si(111) substrates at different conditions have been investigated. Transmission electron diffraction shows the coexistence of domains having the Cu-Au and chalcopyrite structure. X-ray diffraction analysis allows the estimation of the relative amount of the phase domains, which is dependent on the growth conditions of the films. The films also present additional modes in the Raman spectra, together with the ones that are chalcopyrite related. The relative intensity of the additional modes directly correlates with the estimated amount of Cu-Au ordered phase. This supports the interpretation that the additional Raman modes are related to Cu-Au ordered domains. Group theory analysis is in agreement with the symmetry of the observed modes. The phonon frequency of the Cu-Au assigned Raman mode is also in excellent agreement with the first-principles frozen-phonon calculations. (C) 2002 American Institute of Physics.