HIGH RESOLUTION X-RAY MEASUREMENTS OF STRAIN-MEDIATED DIFFUSION IN CuInSe2, P. Fons, S. Niki, A. Yamada, M. Uchino and H. Oyanagi, pp. 201-211

CuInSe2 is a direct bandgap material that assumes the chalcopyrite structure (space group I4̄2d). Due to its large optical absorption coefficient (α ∼ 10 cm−1), its use in thin film polycrystalline solar cells is an active research topic. As most of the research effort to date has been applied directly to polycrystalline film formation for use in solar cell applications and relatively little attention has been paid to fundamental intrinsic material properties, there is a need to further investigate basic optical and structural properties of single crystal material. Due to the fact that it is difficult to prepare stoichiometric material using bulk growth techniques, we have employed molecular beam epitaxy to grow epitaxial layers of CuInSe2 (a=0.57821 nm, c=1.1619 nm) on both GaAs (a=0.56537 nm) and relaxed, nearly lattice matched, linear-graded buffer InxGa1−xAs pseudosubstrates using molecular beam epitaxy. All films were grown at 450− 500◦C using elemental sources of In (7N), Cu (7N), and Se (6N) and were prepared under Se overpressure conditions. High resolution x-ray diffraction using a Ge (220) four crystal monochromator as well as cross-sectional electron microscopy were used to study the as grown films. X-ray analysis found that in the case of CuInSe2 grown on a GaAs substrate interdiffusion of Ga into the relaxed CuInSe2 layer occurred, while in the case of the pseudosubstrate, no interdiffusion was observed. Photoluminescencebased and positron annihilation analysis of point defects in the material will also be presented as well as substrate annealing effects.