Electrical properties and electronic structure of Cu1−xZnxInSe2 and Cu1−xZnxInS2 single crystals

• Temperature dependence of electrical conductivity of Cu1−xZnxInS2 and Cu1−xZnxInSe2 is studied.
• At ~100 to 27 K, the hopping mechanism of electrical conductivity becomes dominant.
• The main parameters of the hopping conductivity have been determined.
• Electronic structure of Cu1−xZnxInS2 is studied by XPS and XES methods.
• Cu1−xZnxInS2 single-crystal surfaces are sensitive to Ar+ ion-bombardment.

Temperature dependence of the electrical conductivity of CuInS2–ZnIn2S4 and CuInSe2–ZnIn2Se4 solid solutions possessing n-type conductivity has been studied. It has been established that when the temperature decreases down to ~100 to 27 K, the hopping mechanism of electrical conductivity with a variable jumping length between localized states positioned in a narrow energy band near the Fermi level becomes dominant. The main parameters of the hopping conductivity have been determined. At higher temperatures (150–300 K), in the CuInSe2–ZnIn2Se4 single crystals containing 15 and 20 mol% ZnIn2Se4 the thermally activated conductivity with activation energy of 0.018 and 0.04 eV, respectively, is detected. Among the CuInSe2–ZnIn2Se4 single crystals, samples with 5 and 10 mol% ZnIn2Se4 were found to be close to degenerate semiconductors. Temperature dependences of the electrical conductivity of CuInS2–ZnIn2S4 single crystals are described by a more complicated function that may indicate a competition of several conduction mechanisms in these compounds. For the CuInS2–ZnIn2S4 solid solutions, X-ray photoelectron core-level and valence-band spectra have been measured for both pristine and Ar+ ion-bombarded surfaces. Our results indicate that the Cu1−xZnxInS2 single-crystal surfaces are sensitive to Ar+ ion-bombardment. Additionally, for the Cu1−xZnxInS2 crystal with the highest ZnIn2S4 content, namely 12 mol% ZnIn2S4, the X-ray emission bands representing the energy distribution of the Cu 3d, Zn 3d and S 3p states have been measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum.