Co Cluster Formation Induced by Cu Codoping in Co:ZnO Semiconductor Thin Films

Here we report that the occupation sites of Co atoms in ZnO matrix could be effectively tuned by the concentration of Cu codopant. The Co Cu codoping effect has been revealed by a combination of X-ray diffraction and Xray absorption fine structure spectroscopy techniques for Zn0.95-xCuxCo0.05O (0.005 <= x <= 0.08) thin films grown by pulse laser deposition at 923 K. Specifically, at the low Cu doping levels (x <= 0.02), the Co(+2) ions are substantially incorporated into the ZnO lattice; upon increasing the Cu concentration to 0.03 or higher, partial formation of Co(0) species occurs, and its proportion rises rapidly with the Cu concentration. Further analysis shows that the Cu codopants are precipitated to form Cu(0) metallic phase in all the samples. We propose a competition mechanism between the Co(0)-Cu(0) metallic interactions and the dissolution of Co ions in ZnO to interpret these findings.