Void formation and surface energies in Cu(InGa)Se2

The spontaneous formation of voids has been observed in Cu(In,Ga)Se-2 films deposited by multistage evaporation processes but was not found commonly in single-stage evaporated material. These voids may be isolated in the grains or may occur at the grain boundaries. The voids exhibit strongly faceted geometries with interior surfaces being close-packed {112} planes of the chalcopyrite structure. A model based on the Kirkendal effect [Trans. AIME 171, 130 (1947)] and the interdiffusion and phase reaction in the bilayer process is proposed to explain the observation. The void shape is analyzed and an approximate Wulff construction [Z. Kristallogr. Mineral. 34, 449 (1901)] is used to estimate the relative surface energies of the predominant facets. Certain dislocation cores are also found to be unstable and convert to nanovoids in the presence of sufficient atomic vacancies moving in the lattice. (c) 2006 American Institute of Physics.