Fabrication and morphological, optical, and electrical characterisation of Cu-doped ZnO nanorod/coronene nanowire hybrid heterojunctions

Abstract

The electrochemical deposition technique was employed to grow 1% and 3% Cu-doped ZnO nanorods on glass/ITO substrate. Then, coronene nanowire was deposited on the 1% and 3% Cu-doped ZnO surfaces via the thermal evaporation technique as an interfacial layer of hybrid heterojunctions. Structural analyses of different ratios of the Cu-doped ZnO layers revealed that they contain ZnO, CuZn, Cu2O and Cu16O14.15 phases, and further that a monoclinic coronene crystal structure could be detected from the XRD spectrum of ITO/coronene thin film. The elemental composition of the1% and 3% Cu-doped ZnO layers was investigated via SEM-EDX from which it was observed that the proportions of the elemental weight of Zn, O, and Cu were 73.4%, 23.5% and 3.1%, respectively, for 1% Cu- doped ZnO, and 71.2%, 21.1%, 7.7% for 3%Cu-doped ZnO. The surface morphological analyses revealed that the inorganic layer crystallised as hexagonal pillar nanorods and the organic layer as nanowires. It was also observed that the nanorod thickness increased from 130–230 nm to 270–450 nm with increasing Cu ratio. As a result of the optical analyses of the hybrid heterojunctions, it was found that the maximum absorption region of the heterojunctions was in the near-ultraviolet region and that they had very low transmittances (0.6%–0.77%). In addition, the absorption coefficients and the band gap energy were ≈ 107 (m−1) and were 3.09–3.25 eV, respectively, while the band gap energy of coronene thin film on ITO was 2.90 eV. Electrical analyses of Ag/ZnO:1%Cu/coronene/Ag and Ag/ZnO:3%Cu/coronene/Ag heterojunctions were performed in the ±0.4 V potential range in a dark environment at room temperature, and diode parameters were determined using various methods. It was found that Ag/ZnO:1%Cu/coronene/Ag and Ag/ZnO:3%Cu/coronene/Ag diodes had high rectification ratios with the values of 250 and 1140, respectively. It is also obvious that while the increase in Cu doping ratio increased the diode ideality factor, series resistances and barrier heights ranged from 1.31 to 13.7, 17 to 3283 Ω, and 0.43 to 0.55 eV, respectively, it decreased the reverse saturation current from 8.1 × 10–3 A to 8.2 × 10–5 A.