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Investigation of structural, optical, electrical, and optoelectronic properties of Co-doped ZnO thin films

NESLIHAN UZAR1,2,* , UBADE ABDULAZIZ3

Affiliation

  1. Department of Physics, Science Faculty, Istanbul University, Vezneciler, 34134 Istanbul, Turkey
  2. Nanomaterial Characterization and Device Design Lab, Department of Physics, Science Faculty, Istanbul University, Vezneciler, 34134 Istanbul, Turkey
  3. Institute of Science, Istanbul University, Suleymaniye, Istanbul, Turkey

Abstract

In this study, undoped ZnO and cobalt (Co)-doped ZnO thin films with varying Co dopant concentrations (Zn1-xCoxO, x=0.01, 0.02, 0.03, and 0.05) were successfully fabricated on the glass and p-type silisyum (Si) substrates using the sol-gel dip coating and spraying methods. All thin films were found to be pure and exhibited a wurtzite ZnO polycrystalline structure with a preferred orientation along the (002) plane. The produced thin films exhibited nanofiber surface morphologies composed of nanodots. It was observed that the surface homogeneity of the thin films improved with Co doping, with the most favorable outcome observed in the 1% Co-doped ZnO sample. Additionally, it was noted that the crystal size of ZnO decreased with Co doping from 25 nm to 14 nm. At low cobalt doping ratios, no significant changes were observed in the optical transmittance and band gap energy of ZnO. However, with higher doping amount (5% Co doping), a decrease in optical transmittance from 70% to 55% and a reduction in the band gap energy from 3.22 eV to 3.05 eV were observed. For low doping rates, no significant change in the electrical properties of ZnO thin films was observed; however, with 5% Co doping, the resistance value of the ZnO thin film increased from 2.3x104 Ω to 4.0x106 Ω, accompanied by a decrease in leakage current from 1.9x10-6 A to 3.8x10-9 A. Finally, the efficiencies of the obtained thin films as solar cells and photodiodes were investigated under both dark and light conditions of 100 mW/cm2. It was observed that Co doping decreased the performance of ZnO as a solar cell. However, it was found that the produced Au/ Zn0.99Co0.01O/p-Si diode was highly suitable for use as a photodiode for visible light sensor applications, with a photosensitivity value of 1.27x10-1AW-1, while pure ZnO is active in the UV region. Since the structural and photodiode properties of ZnO were enhanced by 1% Co doping, this sample held promise for optoelectronic devices..

Keywords

Co-doped ZnO, Photovoltaic cell, Photodiode, SEM, EDS, XRD.

Submitted at: Sept. 25, 2023
Accepted at: July 30, 2024

Citation

NESLIHAN UZAR, UBADE ABDULAZIZ, Investigation of structural, optical, electrical, and optoelectronic properties of Co-doped ZnO thin films, Journal of Optoelectronics and Advanced Materials Vol. 26, Iss. 7-8, pp. 288-306 (2024)