Fabrication of discrete gallium nanoislands on the surface of a Si(001) substrate using a focused ion beam

Abstract

A gallium focused ion beam (FIB) has been used to implant Ga at specific sites on the surface of undoped Si(001) substrates. Upon annealing at 600 °C, discrete nanoscale surface islands form within the FIB patterned regions when the total Ga ion dose, or fluence, is greater than 1.0 × 10(16) ions cm( - 2). The number of islands depends on the size of the irradiated region and a single island can be achieved for a FIB milled region that is 100 nm × 100 nm. The average sizes of the islands were found to range from 24.5 nm when exposed to a total ion dose of 1.2 × 10(16) ions cm( - 2) to 45 nm for a dose of 3.0 × 10(16) ions cm( - 2). We have confirmed that these surface islands are metallic Ga by performing a selective chemical etch that removes the islands and by transmission electron microscopy characterization. These patterned Ga surface templates could serve as nucleation sites for the lateral arrangement of discrete quantum dot structures.

Generation of 3D nanopatterns with smooth surfaces

“…The diameter and the density of these islands are again dependent on the applied Ga dose. Further, matching the findings of [31] for Ga doses below 1.9 •10 16 1 cm 2 , no islands are observable, however the area shows a distinct black color, which indicates the Ga is still contained in the Si matrix. Moreover, the size of the segregated islands depends on the scanning speed during implantation.…”

“…As diffusion is pronounced at higher temperatures, it is also expected that Ga diffusion, formation of Ga clusters, and Ostwald ripening are accelerated for high substrate temperatures. Similar to the experiment performed in [30,31], an SEM investigation comparing Ga implantation at room temperature and at elevated substrate temperatures (300 °C) is displayed in figure 9. At room temperature with an increasing Ga dose, the SE emission (brightness) of implanted areas increases while a smooth, featureless surface structure is maintained (not shown).…”

Combining focused ion beam and atomic layer deposition in nanostructure fabrication

“…The movement of the excess gallium is thus limited to the amorphized surface layer and the surface. It should be noted that segregation of small gallium nanoislands was observed by Wang et al already at doses of 2.9 × 10 16 ions cm −2 upon annealing at 500 • C [13]. Milling the feature in figure 1(a) requires a much higher ion dose of 4.2 × 10 17 ions cm −2 .…”

“…Ion implantation and amorphization of the milled substrate cause degradation of functional material properties [7][8][9]. Furthermore, during any post-annealing, the implanted gallium may form subsurface gallium clusters and surface nanoislands [10][11][12][13] which roughen the milled surface.…”

Taming of Ga droplets on DLC layers—size tuning and local arrangement with nanometer accuracy

“…The high surface tension of Ga leads to the evolution of nanospheres on top of irradiated DLC areas. The phenomenon of this thermal driven segregation and formation of nanoparticles was recently investigated by Wang and Gray for Ga nanoislands on implanted silicon [17] and by Kometani and coworkers for Ga droplets on DLC layers grown by FIB-assisted chemical vapor deposition [18]. It was shown that after annealing the size and areal density of segregated Ga-NPs strongly depend on the incorporated amount of Ga in a certain volume of the layer.…”