Figure 9.

Results of an optimization study of the yield of vertical GaAs nanowires, grown by a self-catalyst method on silicon substrate by the hole aspect ratio in the SiO₂ mask template used to assist the growth. Different values of the aspect ratio d/h were obtained using three different oxide thicknesses h of 10, 15, and 20 nm (corresponding to the red, blue, and green data points, respectively), and different diameters d. All samples were grown under the same growth conditions. The central graph shows the dependence of the vertical yield for the nanowire arrays as a function of the hole aspect ratio, while the inserts show 20° titled SEM micrographs of the samples with the best (upper part images) and worst (lower part images) yields. The maximum yields were obtained for the aspect ratios between 4 and 6 for all three oxide thicknesses used. Outside this range, the yield is compromised by the presence of parasitic growth. The central graph reports also the results of Ref. [104], following the same trend and represented by the yellow points (Reprinted with permission of Ref. [3]).