REACTIVE MAGNETRON SPUTTERING OF CuInS_2 ABSORBERS FOR THIN FILM PHOTOVOLTAIC: RELATION BETWEEN DEPOSITION PARAMETERS AND FILM MORPHOLOGY

摘要

For the preparation of high-quality CuInS_2 absorber films, two film properties are decisive: large crystallites and compact film morphologies. In this work we investigate the influence of the deposition parameters discharge power and substrate bias, on the morphology and chemical composition of CuInS_2 films, which were prepared by reactive magnetron sputtering (radio frequency) in H_2S/Ar atmosphere. A lateral concentration distribution along the substrate axis, which is caused by the arrangement the copper and indium cathodes in our sputtering equipment, was used to study the influence of the Cu-to-In ratio on the film growth. At a Cu-to-In ratio of one, which can be adjusted by the discharge powers at the copper and indium target to be positioned at the middle of the substrate, the crystallites in the film are small in size and separated by crevices from each other. In order to achieve compact CuInS_2 films, the negative substrate bias was varied systematically (-15V to -150 V). The influence of the ion assistance, i.e. the impact of positive argon ions onto the growing film, was investigated with respect to the chemical composition and the morphology of the films.