Multi-staged sol-gel synthesis of Mg doped ZnO/CuO core-shell heterojunction nanocomposite: dopant induced and interface growth response

The effect of Mg dopant and CuO coupling of the synthesized Mg doped ZnO/CuO core-shell heterojunction composite thin film grown over ITO substrate has been investigated. The device structure composed of Mg doped ZnO nanoparticle cores coated with CuO shells synthesized via multi-staged sol-gel approach and deposited on ITO glass substrate by spin coating. The structural response analyzed by XRD reveals that Mg incorporation did not alter the hexagonal wurzite feature of ZnO. The composite maintained the same prominent (1 0 0) and (0 0 2) peak identities of ZnO while peaks (1 1 0) and (2 0 2) belongs to cubic monoclinic CuO appeared along with reduction of D on the analyzed phases, and the finding agrees with the FESEM morphologies. Furthermore, FESEM observation reveals that the smaller CuO particle clusters were grown around ZnO particles forming a coarsened shell. The core-shell structure was further verified by TEM observation. EDX analysis confirmed the complete transformation of the starting materials. XPS analysis confirmed the existence of ZnO and CuO compositions as well as Mg phase in the composite. The optical response observed with Uv-Vis spectroscopy reveals a slight bandgap narrowing with an increase in absorbance range in Mg:ZnO/CuO sample due to present of Cu2+ species and defects related contributions. The observation suggests that the blue-shift effect of Mg doping contribute in balancing the narrow-bandgap CuO overall redshift effect on the composite. The electrical responses documented by J-V characteristics showed evident rectification of both undoped and doped composite samples, implying the formation of p-n junction of a diode. Both samples exhibit non-ideal behavior of I-V with high ideality factor of 4 in baseline sample (ZnO/CuO) and 3.7 in doped sample (Mg:ZnO/CuO). Mg:ZnO/CuO has improved properties compared to baseline device given by lower threshold voltage and lower ideality factor. The findings could provide a promising insight into Mg doped ZnO/CuO bulk heterojunction nanocomposite system with core-shell structure and its potentials in optoelectronics and sensor applications.