Multi-technique investigation of Ni-doped ZnO thin films on sapphire by metalorganic chemical vapor deposition

Optical and material properties of nickel-doped zinc oxide (ZnO-Ni) grown by metalorganic chemical vapor deposition with varying Ni source flow rates are investigated. ZnO-Ni showed a good crystal quality with (002) orientation but deteriorated at high Ni source flow rates. Photoluminescence responses show a reduction in the bandgap of ZnO-Ni with an increase in the Ni source flow and also with an increase in the temperature. Ni-doping can enhance luminescences at low concentrations (<25 SCCM and ∼2%) and suppress at high concentrations. Ni-related defects occur more toward the surface than bulk of the thin films. Longitudinal optical phonon replicas named 1LO and 2LO redshifts at low Ni source flow rates ≤100 SCCM with an increase in the temperature from 14 to 300 K, but exhibits an “S-shaped” red-blue-red shift with a dip at 50 K at higher Ni source flow rates (150 SCCM). Ni-doping also induces asymmetric crystal vibrations and rougher surfaces with the Ni incorporation. This study enhances the understanding of Ni-doped ZnO that is needed to apply transition-metal doped ZnO for various optoelectronic applications.