Synthesis and characterization of undoped and copper-doped zinc oxide nanowires for optoelectronic and solar cells applications

This work concentrated on the synthesis of undoped and Cu-doped ZnO nanowires (NWs) by vapor transport method as
well as on their physical and chemical characterizations. All X-ray diffraction patterns were indexed to ZnO single phase
of hexagonal structure, and no Cu or Cu compounds characteristic peaks were observed. The evaluated Cu at.% was proportional
with Cu ratios used in the source alloys. NWs morphology with quite long and smooth surfaces was observed for
undoped sample, whereas NWs with agglomerations of particles were observed for higher Cu-doped samples. The overall
transmittance decreased with increasing Cu doping ratio with a red shift for the onset of absorption. The optical energy gap
was decreased from 3.33 to 3.10 eV upon increasing the Cu ratio from 0 to 5 at.%. Two emission bands were observed in
the photoluminescent spectra at 385 and 545 nm, and they were strongly tailored via Cu doping. All the samples exhibited
semiconducting behavior with two activation energies. The sensitivity to the NO2
gas was increased with Cu doping ratio.
The magnetization measurements revealed ferromagnetic behavior for all the NWs samples at room temperature.