Influence of cation-vacancy defects on the properties of CuInSe2–ZnIn2Se4 solid solutions

Abstract CuInSe2–ZnIn2Se4 n-type semiconductor crystals were grown by the horizontal variant of the Bridgman method. Their band gap was estimated from the position of the intrinsic absorption band edge. The obtained values of the band gap vary monotonically with the composition of the compounds: at 300 K they increased from 1 eV up to 1.08 eV with increasing amount of ZnIn2Se4 in the range of 5–20 mol%. The solid solutions containing 5–10 mol% ZnIn2Se4 had demonstrated weak temperature dependence of the electrical conductivity, high electron density and low photoconductivity. This evidences their nearly degenerate state. In the crystals with 15 and 20 mol% ZnIn2Se4 a variable range hopping conduction mechanism was found to dominate in the range ∼30–110 K and a thermally activated conductivity at T ⩾ 130 K was observed. The determined values of the donor activation energy for the samples with 15 and 20 mol% ZnIn2Se4 were 0.018 eV and 0.04 eV, respectively. The characteristic feature of the spectral distribution of their photoconductivity at 30–70 K is presence of a narrow peak at 1160–1190 nm.