Effects of Cobalt Doping on the Structural, Optical, and Electrical Properties of SnO2 Nanostructures Synthesized by SILAR Method

Undoped and cobalt (Co) doped tin oxide (SnO2) films were prepared onto glass slides via the successive ionic layer adsorption and reaction (SILAR). Variable characterization methods were applied to examine the effects of cobalt impurities on physical properties of SnO2 films. The performed characterization measurements were X-ray diffraction, Ultraviolet-visible spectrometer, Photoluminescence, and Raman. No peak ascribed to Co, SnO, or Sn was found in the XRD spectrum which may indicate the integration of cobalt in SnO2 crystal lattices. And the obtained XRD peaks may be related to the tetragonal rutile phase of pure SnO2. SEM images exposed that the Co dopant atoms affectedthe sample morphologies. The optical analyses showed that the transmittance and reflectance percentages dropped by the introduction of impurities to the SnO2 system as the absorbance values of doped SnO2 samples increased. Thus,a red shift (2.6-1.8 eV) occurred in the bandgapsas Co concentration changed in the films. The Raman spectra of pure SnO2 and Co:SnO2 samples exhibited major peaksaround 481 cm-1, 571 cm-1 and 602 cm-1. In photoluminescence spectrum, it was noted that the emission intensity can both increase or decrease due to the different cobalt doping ratios in the SnO2 nanostructures. Resistance measurements displayed that the resistivity increased with the increment of doping concentration. However, it was shown that the electrical conductivities could be increased after the heat treatment of glass substrates up to 500 oC, a common behavior of semiconductor materials.