Co and Al co-doping for ferromagnetism in ZnO:Co diluted magnetic semiconductors

Co and Al co-doped ZnO diluted magnetic semiconductors are fabricated by a pulsed laser deposition and their electronic structure is investigated using x-ray absorption and emission spectroscopy. The Zn0.895Co0.100Al0.005O thin films grown under oxygen-rich conditions exhibit ferromagnetic behavior without any indication of Co clustering. The Co L-edge and O K-edge x-ray absorption and emission spectra suggest that most of the Co dopants occupy the substitutional sites and the oxygen vacancies are not responsible for free charge carriers. The spectroscopic results and first principles calculations reveal that the ferromagnetism in Co and Al co-doped ZnO semiconductors mainly arises from Al interstitial defects and their hybridization with Co substitutional dopants.