The compositional dependence of structural parameters, and of the force constants of Cu-Se, Ga-Se and In-Se bonds were studied. A compositional gradient along the ingot was created by fusion (1150C) of the components, and subsequent slow-cooling in a vertical furnace. A single chalcopyrite phase was always present along the sample, and the length-wise composition was monitored by means of the energy dispersive analysis of X-ray measurements of slices. The unit-cell parameters, anion displacement and Cu occupation fraction on its sub-lattice were analyzed by means of X-ray powder diffraction and Rietveld refinement. The anion displacement was found to be a function of the Cu defect on its sub-lattice. The existence of associated defects: that is, two Cu vacancies and one Ga on a Cu site, [2V(Cu)+GaCu], was proposed in order to explain the Cu defect in the sub-lattice, and changes in lattice parameter. This led to the existence of BIII vacancies (In+Ga) and up to 8at% of interstitial Cu that also caused changes in the structural parameters. Infra-red reflectance measurements permitted the obtention of atomic vibration modes. By using the Neumann model for chalcopyrites, the force constants for Cu-Se, Ga-Se and In-Se bonds were estimated. These appeared to increase as the occupation of each sub-lattice increased.

Composition Effects on Structural and Optical Infrared Properties of CuInGaSe2. R.Díaz, T.Martín, J.M.Merino, M.León, J.L.Martín de Vidales, F.Rueda: Journal of Applied Physics, 2000, 88[4], 1776-83