Low Energy Implantation of Atomic Hydrogen into CuInS2 Thin Films by an Ion Broad Beam Technique

CuInS₂ thin films were hydrogenated by 300 eV H³⁺ implantation at elevated target temperature (150°C to 250°C). Using Raman spectroscopy, confocal micro-Raman mapping and photoluminescence spectroscopy, the influence of this treatment on the near-surface range of the material is investigated. According to Raman spectroscopy, no lattice damage in the CuInS₂ due to the process could be observed. The secondary phase CuS, however, is selectively removed from the sample during the hydrogenation. This selective etching can be controlled by the implanted hydrogen dose and the temperature of the sample. A similiar result was obtained for CuInSe2 single crystalline material, containing micrometer-sized Cu_xSe_y precipitations, which were also selectively removed after hydrogenation. The CuInSe₂ surface becomes In-rich within a depth, significantly exceeding the implanted range, again with no observable lattice damage. A chemical process in the atomic hydrogen rich implanted near-surface layer, leading to the formation of volatile Cu-(S,Se)-H compounds, accompanied by the diffusion of Cu from the bulk, is proposed to explain these experimental results. Thus, the low energy hydrogenation technique can be used effectively for controlled changes in the near-surface stoichiometry and for the selective removal of secondary phases.