Effects of In or Ga doping on the growth behavior and optical properties of ZnO nanorods fabricated by hydrothermal process

ZnO nanorods doped with In or Ga were synthesized by a facile hydrothermal process on sol-gel deposited ZnO seed layers. The effects of dopants on the morphology, chemical bonding structure, and optical property of the ZnO nanorods were discussed based on the field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) results. XRD and XPS results indicated that In or Ga ions were doped in the ZnO lattice. Undoped and In- or Ga-doped ZnO nanorods had a hexagonal pillar shape and a single crystal wurtzite structure with (001) growth direction. For the doped samples, the average diameter of the nanorods increased, while the number of the nanorods decreased, compared to the undoped sample. In the PL spectra, the near band edge (NBE) emission peaks of both doped samples shifted to a lower wavelength. On the other hand, the intensity of visible emission increased for the In-doped sample, but decreased for the Ga-doped sample. We considered that this variation was related to the different concentrations of the oxygen vacancies between the samples, which had bond strengths of Ga-O and In-O different from that of Zn-O.