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Coalescence of ZnO nanorods grown by chemical bath deposition

  • Autori: Mauro Mosca, Isodiana Crupi, Daniele Carmelo Russotto, Giuseppe Lullo, Roberto Macaluso, Giuseppe Costantino Giaconia
  • Anno di pubblicazione: 2018
  • Tipologia: Abstract in atti di convegno pubblicato in volume
  • OA Link:


In this work, a way to grow isolated and coalesced ZnO nanorods on p-GaN/sapphire structure is presented. Chemical bath deposition [1],[2] was used to grow ZnO nanorods of device-quality on a p-GaN/n-GaN/sapphire template, simply controlling the duration time of the growth process and the concentration of the nutrient solution in the bath. Several p-GaN templates were soaked in a nutrient solution, prepared with different concentration of zinc nitrate hexahydrate (Sigma-Aldrich, reagent grade 98%) and hexamethylenetetramine (Alfa Aesar, ACS 99%) in deionized water, while being heated at a temperature of 80 °C for a period varying from 8 to 25 hours; then, the samples were left in the solution to cool down naturally to room temperature. Increasing the duration of the process leads to compact and sound layers (instead of separated nanorods), as well as the concentration of the solution. Fig. 1 shows the top-view fieldemission scanning electron microscopy (FE-SEM) images of the samples, obtained for different growth time and 70 mM concentration. The first sample (grown for 8 h) exhibits a typical nanorod layout (Fig. 1.a). The nanorods are oriented along the (0001) direction of the substrate. After 15 h, most of the rods coalesce into a unique layer but the uniformity of the latter is broken by several “empty” areas where ZnO does not seem to be grown (Fig. 1.b). After 25 h, the ZnO appears as a sound compact layer with some defects on the surface (Fig. 1.c). In general, an increase of the concentration results in a better coalescence of the rods but too high concentrations stop the growth process. ZnO layer grown for 25 h in 100 mMconcentrated solution (Fig. 2.a) appears to be more compact than in the case of 70 mM concentration. The improved coalescence should be due to the increase of the nanorods diameter with the concentration, as reported in [3]. Concerning the 500 mM sample (Fig. 2.b), surprisingly only several nanoflowers and nanopillars appear to be deposited on the surface; in particular, the latter are not aligned along the (0001) sapphire plane but just placed on the surface with random orientations. Probably the kinetics of the chemical reactions is hindered by the oversaturation of the solution.