Interaction of atomic hydrogen with the surface of Cu-III-VI2 chalcopyrite semiconductors -: A method for controlled stoichiometry variation

To introduce atomic hydrogen into Cu-chalcopyrite samples, low energy broad beam ion implantation into heated targets was used. In addition to the expected hydrogen diffusion into the sample from the implanted thin surface layer, another hydrogen-related effect was observed. As demonstrated for single crystalline CuInSe2, at target temperatures above 150 degrees C a surface layer becomes In-rich. Two phases, the CuInSe2 alpha-phase and a In-rich phase similar to the reported ordered vacancy compounds (beta-phase) coexist, as detected by Raman spectroscopy. The depth profile and the thermal stability of this hydrogen-related compositional variation are investigated. Based on the results we discuss a model of this effect, involving a copper in-diffusion caused by the hydrogenation due to filling of Cu vacancies and possible substitution of Cu by H. The observed beta-phase-like compound is unstable against annealing above 180 degrees C:, but can be restored in a thermal cycling process. Annealing for 1.5 h at 400 degrees C removes it completely and restores the as grown CuInSe2 surface. A decrease of the hydrogen concentration in the surface layer due to redistribution and out-diffusion, followed by the recovery of the Cu content, might be responsible for this behaviour.