Lattice dynamics of the chalcopyrite and defect stannite phases in the Cu-(In, Ga)-Se system

Raman spectra observed for bulk crystals of defect stannite phases in the Cu-(In, Ga)-Se system are analyzed mainly by the dispersion curve calculations with a superposed lattice model, assuming four fundamental structures. The calculations are performed on the basis of the Keating model, solving dynamical matrix of 24×24. Vacancy induced modifications on force interactions between nearest atoms are also discussed with effective bond overlap population and effective charges determined by the DV-Xα calculations for unit cell clusters. Apparently, invariable Raman profiles with respect to the In to Ga molar ratios through the alloy systems are explained by the superposed lattice model.