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

Abstract

CuInSe2–ZnIn2Se4n-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 300K they increased from 1eV up to 1.08eV with increasing amount of ZnIn2Se4 in the range of 5–20mol%. The solid solutions containing 5–10mol% 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 20mol% ZnIn2Se4 a variable range hopping conduction mechanism was found to dominate in the range ∼30–110K and a thermally activated conductivity at T⩾130K was observed. The determined values of the donor activation energy for the samples with 15 and 20mol% ZnIn2Se4 were 0.018eV and 0.04eV, respectively. The characteristic feature of the spectral distribution of their photoconductivity at 30–70K is presence of a narrow peak at 1160–1190nm.