Effect of Ni, Cu, Ni/Cu Co-Doping on the Structural and Optical Properties of ZnO Rods Grown on Porous Silicon
DOI:
https://doi.org/10.48048/tis.2026.13778Keywords:
Porous silicon (PSi), ZnO rods, Nickel doping, Copper doping, Ni/Cu co-doping, HydrothermalAbstract
Zinc oxide (ZnO) is primarily used as a semiconductor material for photoanode applications, but its wide bandgap, fast charge recombination, and low conductivity limit its performance. Doping with Ni or Cu is necessary to narrow the bandgap, improve visible-light absorption, and enhance charge separation. Porous silicon (PSi) is employed as a substrate to enhance ZnO nucleation, increase surface area, and improve light absorption through its porous structure. Therefore, this study investigated the structural and optical properties of the Ni-doped, Cu-doped, and Ni/Cu-co-doped ZnO rods grown on porous silicon (PSi) substrates to optimize their potential for photoanodes. PSi was fabricated on n-type Si (100) wafers using the green laser-assisted electrochemical anodization method at 2 mA/cm2 for 10 min. Ni-doped, Cu-doped, and Ni/Cu-co-doped ZnO solutions were coated on the PSi substrates using a spin coater, and then the hydrothermal techniques were performed at 90°C for 9 h and followed by annealing at 450°C for 30 min. SEM analysis revealed hexagonal ZnO rods with average diameters ranging from 156.59 to 211.94 nm, increasing with Ni/Cu doping. XRD confirmed the presence of hexagonal wurtzite ZnO along with cubic phases of Si, Ni, Cu, and NiO, triclinic SiO₂ and monoclinic CuO. UV-Vis reflectance spectra showed enhanced reflectance and reduced bandgap energy with doping, indicating successful incorporation of Ni²⁺/Cu²⁺ into the ZnO. Specifically, the estimated band gap energies were 3.07 eV for pure ZnO (PZ), 3.05 eV for for Ni-doped ZnO rods (PZNi5%), 3.03 eV for Cu-doped ZnO rods (PZCu5%), and 3.02 eV for Ni/Cu-co-doped ZnO rods (PZNiCu5%). The smallest band gap (3.02 eV for PZNiCu5%) is advantageous for heterojunction solar cells as it enables broader visible-light harvesting.
HIGHLIGHTS
- Ni-doped ZnO rods, Cu-doped ZnO rods, and Ni/Cu-co-doped ZnO rods were successfully grown on porous silicon (PSi) substrates using a hydrothermal method.
- Doping modified the morphology of ZnO rods, producing flower-like hexagonal structures and increasing the average rod diameter.
- Successful incorporation of Ni²⁺ and Cu²⁺ ions into the ZnO lattice was verified by EDX, XRD, and optical analyses.
- Ni and Cu incorporation reduced the ZnO bandgap energy from 3.07 eV to 3.02 eV, indicating enhanced visible-light absorption.
- Ni/Cu co-doped ZnO rods exhibited the lowest bandgap and improved crystallinity, demonstrating strong potential for heterojunction photoanode applications.
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