Nickel doping in zinc oxide by MOCVD: structural and optical properties

Nickel-doped zinc oxide (ZnNiO) was grown on sapphire by metal organic chemical vapor deposition (MOCVD) with varying Ni content under two growth conditions of 400°C/100 Torr and 450°C/30 Torr. Elemental composition indicated that Ni could occupy Zn and O/interstitial sites in ZnNiO. Ni-doping in ZnO resulted in shifts in X-ray diffraction (002) peak, and introduced a (111) phase. Absorption spectrum showed a reduction in near band edge with Ni content in both the samples’ sets. Samples grown at 400°C/100 Torr had a band gap reduction from 3.276 eV to 3.269 eV, while those synthesized at 450°C/30 Torr showed reduction from 3.287 eV to 3.260 eV. The bandgap reduction rate was influenced by growth conditions, and sites activated for Ni incorporation during the growth. Nickel could introduce shallow energy states near the valence band in ZnNiO, and result in a reduction in the bandgap. A potential for bandgap tunability, and controllable introduction of energy states in zinc oxide with transition metal doping by MOCVD, could widen the application range of zinc oxide-based materials for energy harvesting and electronics.