Interplay between Occupation Sites of (Co, Cu) Codopants and Crystal Orientation of ZnO Matrix

Elemental codoping has been an effective way to modify the structural and electronic properties of semiconductors. By use of X-ray diffraction and X-ray absorption fine structure spectroscopy, we show that the spatial occupations of Co and Cu codopants in ZnO thin films could be regulated by the crystal orientation of the matrix prepared by pulsed laser deposition at different temperatures. At deposition temperatures lower than 300 °C, the ZnO matrix was grown along the [201] preferential orientation, with the substitutional incorporation of Co dopants and formation of metallic Cu nanoclusters. Increasing the growth temperature to 300 °C or higher drives a transform of the ZnO film to the c-axial [002] preferred orientation. Consequently, the Cu atoms aggregate into larger fcc-structured Cu nanocrystals that attract part of the Co dopants to precipitate out as metallic clusters. The relation between the growth orientation of ZnO thin films and the occupation positions of Co/Cu codopants is discussed in terms of the temperature-dependent mobility and formation energy of the doping atoms.