Solubility of co-doped Cu ions in Zn0.95Co0.05O diluted magnetic semiconductors

Cu and Co ions co-doped Zn0.95-xCuxCo0.05O (0 <= x <= 0.08) diluted magnetic semiconductors (DMSs) prepared by the sol-gel method were investigated by x-ray absorption fine structure (XAFS). Although the Co K-edge XAFS data indicate that the doped Co ions are located substitutionally at the Zn sites for all the Zn0.95-xCuxCo0.05O DMSs, the CuK-edge XAFS analysis combined with XRD results reveals that the doped Cu ions are separated to form a CuO phase for samples calcined at 1073 K. After being sintered at a higher temperature of 1473 K, the Cu ions with low Cu concentration (x <= 0.02) are substantially incorporated into the ZnO host lattice, while a small proportion of CuO clusters still coexist in the samples with a higher Cu concentration (x <= 0.05). The solubility of the doped Cu ions in Zn0.95Co0.05O DMS is estimated as about 0.04. The results provide experimental guidance in the synthesis of the co-doped ZnO based DMSs.