Extra Raman modes in CdS during cubic to hexagonal structural transformation

Cubic CdS thin films were grown on glass substrates by chemical bath deposition at 80 °C. By means of thermal annealing (TA) in an Ar + S 2 atmosphere in the 224–403 °C range, the cubic metastable zinc blende (ZB) crystalline structure gradually transforms to the stable wurtzite (W) phase. The critical temperature of this phase transformation is around 300 °C, where the material passes from a ZB‐dominated to a W‐dominated phase. Raman spectra obtained at room temperature in parallel and crossed polarizations exhibit extra vibrational modes only when TA is at 344 °C. These experimental findings were explained by considering the critical density of interstitially located Cd 2+ ions and their influence to the lattice dynamics of the system. We assumed a model in which the interatomic bonds in the CdS lattice are physically described by a set of springs obeying Hooke's law. The calculated wavenumbers agree remarkably well with the experimental data considering the simplicity of the approach. Copyright © 2002 John Wiley & Sons, Ltd.