Unusual enhanced photoluminescence from highly lattice mismatched ZnO/Cu₃N multilayer films

ZnO/Cu₃N multilayer films with different oxygen partial pressures are deposited by radio frequency magnetron sputtering method. The crystal structures and optical properties are analyzed by using X-ray diffraction (XRD) patterns, reflectance spectra, absorbance spectra and PL spectra. Both Cu₃N (111) and ZnO (002) diffraction phases are observed in the XRD patterns of all the ZnO/Cu₃N multilayer films. In addition, XRD results also indicate that the lattice mismatch f_m is 38.28% for ZnO/Cu₃N multilayer film with 5:25 sccm and reaches the maximum value among all samples. Generally, highly lattice mismatched multilayer films always undergo serious residual strain, which cause PL quenching. However, in this work, the intensity of three emission peaks ranging from violet to blue-green wavelength in ZnO/Cu₃N multilayer films attain to strongest at a low oxygen partial pressure of 5:25 sccm. Based on experimental results, we propose unusual enhanced photoluminescence (PL) mechanism from highly lattice mismatched ZnO/Cu₃N multilayer films.