Photoemission investigation of the electronic structure at polycrystalline CuInSe2 thin-film interfaces

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Abstract
The surface versus bulk composition and electronic structure of polycrystalline CuInSe2 thin‐film interfaces were studied by synchrotron radiation soft‐x‐ray photoemissionspectroscopy. An n‐type In2Se3/CuIn3Se5surface layer forms on enhanced‐grain polycrystalline thin‐film p‐type CuInSe2 during fabrication. Enhanced‐grain CuInSe2 films were sputter etched (500 V Ar) and analyzed in situ to determine core‐level binding energies and Fermi‐level positions for the n‐type surface and the p‐type CuInSe2 bulk within ±0.1 eV. The transition between the n‐type surface and the p‐type bulk was experimentally observed by noting the change in the position of the valence‐band maximum relative to the Fermi level E F . From these measurements, the valence‐band offset ΔE v between the layers was determined to be 0.50 eV. Measurement of the work functions φ was also completed and reveals φ=4.75 eV for the In2Se3 (CuIn3Se5) surface layer and φ=4.04 eV for the bulk CuInSe2. Combining these results allows construction of a surface band diagram for this device configuration as well as determination of the relationship between composition, electronic structure, and device performance.