Nucleation of Ga droplets on Si and SiO_xsurfaces

Abstract

We report on gallium droplet nucleation on silicon (100) substrates with and without the presence of the native oxide. The gallium deposition is carried out under ultra-high vacuum conditions at temperatures between 580 and 630 °C. The total droplet volume, obtained from a fit to the diameter-density relation, is used for sample analysis on clean silicon surfaces. Through a variation of the 2D equivalent Ga thickness, the droplet diameter was found to be between 250-1000 nm. Longer annealing times resulted in a decrease of the total droplet volume. Substrate temperatures of 630 °C and above led to Ga etching into the Si substrates and caused Si precipitation around the droplets. In contrast, we obtained an almost constant diameter distribution around 75 nm over a density range of more than two orders of magnitude in the presence of a native oxide layer. Furthermore, the droplet nucleation was found to correlate with the density of surface features on the 'epi-ready' wafer.

Lithography-free positioned GaAs nanowire growth with focused ion beam implantation of Ga

“…For temperatures above 600 C, the formation of Ga droplets with typical diameters around 80 nm could be observed, which is comparable to previously reported data. 13 These droplets then served as nucleation centers for the nanowires, while the native oxide of the Si substrates, being stable up to 900 C, reduces parasitic nanowire formation in between. GaAs nanowire growth was performed under Ga-rich growth conditions 10,14 with typical equivalent layer Ga growth rates of 0.1 lm/h.…”

“…In general, the measured range of nanowire diameters agrees well with data for Ga droplets of similar densities, nucleated at 630 C on Si (1 0 0) surfaces with native oxide. 13 Although lower doses seem to lead to slightly larger diameters around 78 nm, compared to 61 nm for higher implantation doses or 73 nm for random wires, this trend can be traced back to the nanowire density per unit area. More nanowires locally lead to a reduction of the III/V ratio and therefore to larger nanowire diameters.…”

“…[10][11][12] Without position control, however, the nucleation process leads to a rather broad diameter distribution, as well as nanowire growth in random spots with local variations in their density. 13,14 Various lithographic processes for the positioning of catalyst metal have been developed. Yet, they all share the fact that they require organic substances as the etch mask, lift-off mask, imprint material, or simply as solvent.…”

The Growth of Ga2O3 Nanowires on Silicon for Ultraviolet Photodetector

“…We believe that Ag has the role to improve wettability, which will enhance the homogeneous appearance of Ga 2 O 3 nuclei that could lead to dense nanowires. The contact angle of Ga on a silver film is 30° [30], and on a silicon substrate, it is 73.9° [31], leading to better wetting of Ga on Ag surface and uniform growth of Ga 2 O 3 nanowires (Figure 3).…”

Novel Approach to Synthesize Nanostructured Gallium Oxide for Devices Operating in Harsh Environmental Conditions

“…It has been shown by our group that coating the surface with a thin film of metallic material, such as silver, prior to the oxidation process leads to a more homogeneous coating and a denser nucleation of Ga 2 O 3 due to the low contact angle [36]. The contact angles of Ga on a silver film and silicon substrate are 30 • and 73.9 • [37,38], respectively, resulting in a better wetting of Ga on Ag surface and the uniform growth of Ga 2 O 3 nanowires. However, this process requires the sputtering technique, which increases the cost of the fabrication.…”