Surface-properties relationship in sputtered Ag thin films: Influence of the thickness and the annealing temperature in nitrogen

Metal layers with high roughness and electrical conductivity are required as back-reflector electrodes in several optoelectronic devices. The metal layer thickness and the process temperature should be adjusted to reduce the material and energetic costs for the electrode preparation. Here, Ag thin films with thickness ranging from 30 to 200 nm have been deposited by sputtering at room temperature on glass substrates. The structure, morphology, optical and electrical properties of the films have been analyzed in the as-grown conditions and after thermal treatment in flowing nitrogen at various temperatures in the 150-550 °C range. The surface texture has been characterized by the root-mean-square roughness and the correlation length coefficients, which are directly related to the electrical resistivity and the light-scattering parameter (reflectance haze) for the various samples. The increment in the reflectance haze has been used to detect surface agglomeration processes that are found dependent on both the film thickness and the annealing temperature. A good compromise between light-scattering and electrical conductivity has been achieved with 70 nm-thick Ag films after 350 °C heating.