Effect of aluminum incorporation on the microstructure and electrical properties of Cu(InGaAl)Se2 targets

In this study, pentabasic CuInxGayAl1-x-ySe2 (CIGAS) powder was prepared by heating in ethylene diamine at 290 °C for 20 h, using a solvent thermal reaction technique. The microstructures and electrical properties of the CIGAS targets doped with different aluminum content were investigated by XRD, SEM, XPS and Hall Effect techniques. The results indicate that Al doping had an important effect on the electrical properties and microstructure of the CIGAS targets, especially at the (112) crystal orientation. It was found that the peak of (112) clearly shifted to higher 2θ values with the increase of aluminum incorporation, while the peak intensity weakened gradually, thus indicating that the crystallinity of the CIGAS targets decreased. The SEM results revealed that the sizes of the CIGAS grains could be adjusted by varying the stoichiometric ratio of In, Ga and Al, and that the Al incorporation could enhance the density of the CIGAS targets. The XRD and XPS analysis showed that some In and Ga atoms in the crystal lattice of chalcopyrite structure could be replaced with Al atoms in the CIGAS materials. Finally, the electrical properties of the targets were analyzed based on the Hall Effect measurements. The results showed that the conductivity, mobility and carrier concentration of the targets changed significantly along with the increase of the Al incorporation content, and that the mobility reducing may have been a result of Al incorporation, which prevents the grain from growing, followed by high-density target forming.