Hydrogen in CuInSe2 Original Research Article

The surface of vaccum-cleaved and oxidized CuInSe2 single crystals with different deviations from ideal stoichiometry and oxidized CuGaSe2 thin films were exposed to low energy hydrogen ions (300 eV). Besides the removal of surface contaminations within a short exposure time as studied by X-ray photoelectron spectroscopy, this process leads to hydrogen incorporation into the bulk of the material accompanied by copper depletion up to the same depth. In addition, the hydrogen ions influence the defect equilibrium in such a way, that type-conversion from initially p-type to n-type CuInSe2 is possible. In case of Cu-rich material, hydrogen is found to remove the binary phases existing at the surface. A defect chemical model is proposed to explain the experimental observations. Interstitial hydrogen acts mainly as a donor and is able to passivate copper-vacancies (VCu). The Cu-depleted surface layer is the result of electromigration due to the built-in electrical field caused by band bending. Exposure time and sample temperature influence not only the hydrogen diffusion profile, but also the thickness of the Cu-depleted layer and the position of the produced pn-homojunction.