Formation and analysis of graded CuIn(Se1-ySy)(2) films

CuInSe2 and CuInS2 form a continuous solid solution in which the optical ba ndgap varies from 1.0 to 1.55 eV (B. Abid ct al., Proc. IEEE PVSC, 1987 130 5-1308). By reacting CuInSe2 films in a flowing H2S/Ar atmosphere, the film s can be completely converted to CuInS2 or converted to a graded CuIn(Se1-y Sy)(2) film, depending on processing conditions. A phenomenological model o f the reaction/diffusion process is presented wherein H2S reacts with CuInS e2 at the surface to form CuInS2, releasing Se. The CuInS2 and CuInSe2 laye rs interdiffuse, resulting in a S/Se gradient in the structure. X-Ray diffr action (112) line profiles of graded films are compositionally broadened du e to continuously changing lattice parameters. The three-dimensional sulfur distribution was calculated for measured grain size distribution using the formalism of Gilmer and Farrell and used to generate diffraction line prof iles. These were fit to measured line profiles using bulk and grain boundar y diffusion coefficients as fitting parameters, yielding diffusion coeffici ents and activation energies for bulk and grain boundary diffusion processe s. (C) 2001 Elsevier Science B.V. All rights reserved.