Diffusion of sodium in single crystal CuInSe2

摘要

The incorporation of sodium from sodium fluoride in single-crystal CuInSe2 (CIS) is investigated to provide insight into the intra-granular aspects of sodium incorporation in CIS-based thin films. Sodium was incorporated by evaporating NaF onto two CIS crystals of varying compositions and defect structures followed by heating under vacuum. Diffusion profiles show a near-surface reaction before a deeper diffusion zone which follows a complementary error function, confirming Na diffusion into the crystals. Transmission electron microscopy analysis indicates that dislocations do not control the diffusion process. The activation energy of diffusion is similar to 0.7 eV for both crystals. This low activation energy suggests that Na diffusion occurs rapidly through the bulk at temperatures as low as 300 degrees C and helps explain the uniform Na concentration often observed in grain interiors of polycrystalline Cu(InGa)Se-2 thin films. Published by AIP Publishing.