Structural, magnetic and electronic properties of Zn0.94Co0.06O/ZnO heterostructure

In the present work, single layers of ZnO, Zn0.94Co0.06O and Zn0.94Co0.06O/ZnO heterostructure thin film on quartz substrates as well as on Si (111) substrate have been prepared using RF ion beam sputtering. Grazing incident X-ray diffraction (GIXRD), UV–Vis spectroscopy, X-ray absorption near edge structure (XANES), vibrating sample magnetometer (VSM) and photoelectron spectroscopy (PES) were performed to obtain structural, optical, electronic properties. GIXRD measurement confirms Wurtzite structure of ZnO, whereas UV–Vis spectroscopy shows a blue shift of the absorption edge in Zn0.94Co0.06O single layer with respect to ZnO film with band gap of 3.18 and 3.32 eV for ZnO and Zn0.94Co0.06O single layer films, respectively. The O K-edge spectra revealed O 2p hybridization with Zn3d4s/Co3d states, whereas Co L3-edge and Co K-edge XANES spectra confirm Co2+ oxidation state. M-H hysteresis measurement at 300 K shows a weak ferromagnetism for Zn0.94Co0.06O single layer and Zn0.94Co0.06O/ZnO heterostructure thin film. Furthermore, to obtain band offset of Zn0.94Co0.06O/ZnO heterostructure thin films, valance band maximum and core level peaks were measured using PES measurement. The offsets in valance band and conduction band for Zn0.94Co0.06O/ZnO heterostructure thin film were obtained as ~0.41 eV and ~0.55 eV, respectively, and compared with ~0.36 eV and ~0.51 eV, respectively, of Zn0.9Co0.1O/ZnO heterostructure thin films. The results show that a type-II band alignment in the studied system.