Band-gap engineering of Zn1-xGaxO nanopowders: synthesis, structural and optical characterizations

We report the preparation and detailed structural and optical characterizations of single phase gallium doped ZnO nanopowders. A low temperature solution-based technique was developed to synthesize high-purity Zn1−xGaxO (x:0-0.05) nanopowders. Structural and optical characterization experiments were performed using x-ray diffraction (XRD), energy dispersive x-ray spectroscopy, scanning electron microscopy, photoluminescence spectroscopy, Raman spectroscopy, and optical transmission spectroscopy. Analysis of XRD data showed a maximum in the lattice volume for x =0.03 as the Ga concentration increases in the Zn1−xGaxO series. Optical transmission spectroscopy results also showed an initial increase in the band gap (Eg) followed by a decrease for x>0.04. A maximum band gap was observed for the Zn0.96Ga0.04O sample, which has a value of 3.42 eV compared to the band-gap value of 3.31 eV for the undoped ZnO sample. All Zn1−xGaxO nanopowder samples showed a broad photoluminescence spectrum with significant shift in peak positions compared to bulk ZnO sample. The broadening and shifting in luminescence are understood to be caused by the nanocrystalline nature of the material and the presence of deep-level surface defects. These effects were further investigated by Raman microscopy where an increase in the intensity of E1(TO) mode was observed accompanied by the appearance of a few additional Raman active modes.