Comparative evaluation of ZnO nanorod material properties and UV photodetector performance with various transition metal dopings

In this study, we explore the structural, optical, and chemical properties of ZnO nanorods (NRs) grown through various transition metal (TM) dopings of Cu, Ni, Co, Ni-plus-Cu, and Ni-plus-Co, while investigating the effect of these external dopings on the performance of ZnO NR-based ultra-violet photodetectors (PDs) implemented on polyethylene terephthalate substrates. The TM dopings, especially Ni-plus-Cu or Ni-plus-Co co-doping, not only improve the crystalline quality but also significantly suppress the density of deep-level emission defects in as-grown ZnO NRs, as demonstrated by X-ray diffraction and photoluminescence. Furthermore, increased O/Zn stoichiometry from 0.55 (undoped) to 0.78 and 0.83 is achieved when the NRs doped with Ni-plus-Cu and Ni-plus-Co, respectively, as revealed by X-ray photoelectron spectroscopy. The highest current on–off ratio of ~51 and spectral responsivity of ~136 A/W are obtained from the PDs fabricated with the NRs doped with Ni-plus-Co. The response time of the PDs is also improved with TM dopings, and rise time and fall time are reduced to ~1/5 and ~1/4, respectively, in the case of Ni-plus-Co doping compared to the values of the device fabricated with undoped NRs.