Optically enhanced N doped ZnO amorphous nanostructures grown by low cost ultrasonicated sol–gel route

Abstract

N doped ZnO amorphous nanostructures with excellent optical properties were grown by the ultrasonicated sol-gel route. The samples were characterized using structural, morphological and optical studies. XRD patterns confirmed the hexagonal wurtzite structure of ZnO. Increase in nitrogen doping results in effective structural changes like decrease in FWHM of peak (34.30), appearance of additional peaks and removal of previous peaks. The crystallite size of undoped ZnO is calculated at around 5.88 nm and decreases to 3.525 nm, 3.386 nm, and 3.008 nm respectively on gradual increase in nitrogen doping concentration in the samples B: 0.05M, C: 0.1M, and D: 0.2M respectively. The morphological pattern of these nanostructures shows that on increasing the doping of nitrogen, the roughness of the surface increases. An optical study shows that on doping of nitrogen, the bandgap decreases results in absorption shifts in the visible region. Two peaks at 480nm and 685nm are observed due to defects of ZnO surface. The addition of nitrogen generates acceptor levels near the valance band edge. The peak at 450 nm might be due to transition from the conduction band to shallow acceptor levels near the valance band. The presence of a peak near 665 nm indicates the formation of deep holes levels. Significant shift in band edge, the morphological changes and decrease in size indicates successful doping in terms of nitrogen content and homogeneity. Nitrogen doping and metal vacancies stabilize shallow acceptors levels above the valence band in ZnO, thus triggering the stabilization of a p-type conductivity as indicated in luminescence studies.