Photoluminescence from c-axis oriented ZnO films synthesized by sol-gel with diethanolamine as chelating agent

ZnO films were synthesized on SiO2/Si substrates through the sol-gel technique using diethanolamine as chelating agent and annealed in Ar+O2 atmospheres with different O2 flow-rates in the 10-100 sccm range. Samples were studied by scanning electron microscopy and X-ray diffraction, evidencing a nanostructured morphology with a preferential orientation along the (0 0 2) direction (c-axis orientation), which is uncommon when diethanolamine is used as the chelating agent. The room temperature photoluminescence spectra show strong UV emissions at around 375 and 384 nm from near band-edge transitions and phonon replica, and a broad defect-related band extending from the visible to near infrared (∼500-800 nm). The analysis of the defect-related emission band and its various components as a function of the O2 flow-rate is discussed in terms of contributions from specific luminescent point defect centers established during annealing.