In this work, a way to grow isolated and coalesced ZnO nanorods on p-GaN/sapphirestructure is presented. Chemical bath deposition , was used to grow ZnO nanorods ofdevice-quality on a p-GaN/n-GaN/sapphire template, simply controlling the duration time ofthe growth process and the concentration of the nutrient solution in the bath. Several p-GaNtemplates were soaked in a nutrient solution, prepared with different concentration of zincnitrate hexahydrate (Sigma-Aldrich, reagent grade 98%) and hexamethylenetetramine (AlfaAesar, ACS 99%) in deionized water, while being heated at a temperature of 80 °C for aperiod varying from 8 to 25 hours; then, the samples were left in the solution to cool downnaturally to room temperature. Increasing the duration of the process leads to compact and sound layers (instead of separatednanorods), as well as the concentration of the solution. Fig. 1 shows the top-view fieldemissionscanning electron microscopy (FE-SEM) images of the samples, obtained fordifferent growth time and 70 mM concentration. The first sample (grown for 8 h) exhibits atypical nanorod layout (Fig. 1.a). The nanorods are oriented along the (0001) direction of thesubstrate. After 15 h, most of the rods coalesce into a unique layer but the uniformity of thelatter 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 toohigh concentrations stop the growth process. ZnO layer grown for 25 h in 100 mMconcentratedsolution (Fig. 2.a) appears to be more compact than in the case of 70 mMconcentration. The improved coalescence should be due to the increase of the nanorodsdiameter with the concentration, as reported in . 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 thesurface with random orientations. Probably the kinetics of the chemical reactions is hinderedby the oversaturation of the solution.
|Numero di pagine||2|
|Stato di pubblicazione||Published - 2018|