Theoretical and experimental study of effects of Co2+ doping on structural and electronic properties of ZnO

In this study, we theoretically investigated the electronic structure of Zn1-xCoxO using different approaches for the exchange-correlation potential comprising GGA with the on-site Coulomb correlation interaction U to the Zn d orbital (GGA + UZn), GGA with modified Becke–Johnson exchange potential (GGA + mBJ), and (GGA + mBJ + UZn). To support the theoretical results, a Co2+-doped ZnO sample was obtained experimentally by using the microwave–hydrothermal method. Changes in the structural, vibrational, electronic, and magnetic properties induced by the insertion of the Co2+ impurities in the ZnO lattice were determined based on first principles calculations. The theoretical results showed that the 3d orbitals derived from Co2+ appear in the deep region of the band gap. These orbitals are responsible for the magnetic behavior of cobalt doped materials. The energy levels introduced by the Co2+ dopant ions reduced the theoretical band gap value, which was also observed experimentally. The addition of Co2+ ions weakened the Raman mode E2H intensity, which was attributed to the increasing distortion induced by doping. Photoluminescence spectroscopy results indicated a reduction in the visible emission region after adding Co2+ ions, thereby indicating the formation of alternative pathways for the recombination process.