Effect of the composition on the ionic motion in an In-rich chalcopyrite ingot of the Cu–Ag–In–Se system

Abstract

A Cu0.9Ag0.1In3Se5 ingot with a length of 31mm and 10mm of diameter was grown from the pure elements using the Bridgman method. The ingot appeared broken in two separate parts that were cut in several slices 2mm thick. A S1 region, from the bottom to 13.6mm, where the composition varies markedly along its length, but the surface composition is homogeneous in all slices; and a S2 non homogenous region, from 13.6 to the end of the ingot. Composition, X-ray diffraction and Laue diffractogram data of S1 region show the formation of an In rich chalcopyrite single crystal. All homogenous samples have a lower Ag content than that corresponding to the expected composition. The low Ag solubility in the chalcopyrite lattice is possibly due to its larger ionic size as compared to that of Cu. The electrical properties have been analyzed in three samples with different composition by forming a graphite paint/sample/graphite paint solid state device. The sample potential drop, Vm, the current intensity, I, and the Vm(t)/I(t) ratio vary with time when a constant potential is applied to such device. The no reproducibility of the electrical measurements has been observed. Therefore, these compounds are mixed ionic and electronic conductors. This behavior is associated with ionic motion and their subsequent accumulation at the graphite paint/sample interface that leads to the formation of a new potential. The different composition in In rich chalcopyrites indicates a different number of (InCu2++2VCu) defect pairs, DADPs. A relation between the interface potential and the number of DADPS and Ag content has been established. The existence of such interface potential is supported by the discharge processes observed when the solid state device under study is set in short- and open-circuit configurations.