Band structure investigation of chalcopyrite CuInSe₂(001) by angle-resolved photoelectron spectroscopy

Abstract

Clean and ordered chalcopyrite CuInSe 2 surfaces are a precondition for the study of the electronic structure by angle-resolved photoelectron spectroscopy. The preparation of welldefined CuInSe 2 (001) surfaces by the combination of molecular beam epitaxy and a selenium capping and decapping process is described. The surface structure of CuInSe 2 epilayers with different bulk composition is compared and analysed by low-energy electron diffraction.Employing near-stoichiometric surfaces, the valence electronic structure of CuInSe 2 was investigated by angle-resolved photoelectron spectroscopy at the synchrotron source BESSY 2. This is the first study of the valence band structure of a copper chalcopyrite semiconductor material by photoelectron spectroscopy. The valence band dispersion along ΓΤ, i.e. the [001] direction, was investigated by a variation of the excitation energy from 10 to 35 eV under normal emission, and the band dispersion along ΓΝ, i.e. the [110] direction, was analysed by angular scans with hν = 13 eV.The valence bands derived from antibonding and bonding Se4p-Cu3d hybrid orbitals, nonbonding Cu3d states and In-Se hybrid states are clearly indentified. The strongest dispersion is found for the topmost valence band with a bandwidth of ~0.7 eV from Γ to Τ. From Γ to Ν, the observed dispersion was 0.5 eV. The experimental valence bands are discussed in relation to calculated band structures in the literature. * hunger@surface.tu-darmstadt.de F2.2.1 Mater. Res. Soc. Symp. Proc. Vol. 865