Directed Self-Assembly of Ge Quantum Dots Using Focused Si2+ Ion Beam Patterning

Abstract

We show that templating a Si surface with a focused beam of Si2+ or Si+ ions can create suitable nucleation sites for the subsequent growth of self-assembled Ge quantum dots by chemical vapor deposition. To determine the mechanism of patterning we use atomic force microscopy to show that, similar to Ga+ patterning, the formation of a surface pit is required to enable control over Ge quantum dot locations. We find that relatively high implantation doses are required to achieve patterning, and these doses lead to amorphization of the substrate. We assess the degree to which the substrate crystallinity can be recovered by subsequent processing. Using in situ transmission electron microscopy heating experiments we find that recrystallization is possible at the growth temperature of the Ge quantum dots, but defects remain that follow the pattern of the initial implantation. We discuss the formation mechanism of the defects and the benefits of using Si ions for patterning both defects and quantum dots on Si substrates.

Advancements and challenges in strained group-IV-based optoelectronic materials stressed by ion beam treatment

“…Kim et al [41] suggested that even at energies below this threshold, where nuclear stopping predominates and ions undergo frequent elastic nuclear scattering, on average the ion track maintains some directionality and the mechanism described above may still dominate changes in the morphology. This same out-of-plane swelling was also reported for 30 keV Ga + [45] or 60 keV Si ++ [46] implants into bulk Si (a good thermal dissipator), suggesting other mechanisms are also involved in ion-induced swelling, being the former attributed to Ga accumulation at small doses and the latter ascribed to amorphization expansion in the plane followed by outward bowing. Another example to support the miscellaneous reports is when 30 keV Ga + irradiates a gold (Au) thin film [47] in which Au atoms sputtered/coalesce and the replacement of larger Au atoms by Ga causes a contraction on the top layer (delimited by the implantation depth, 7.6 nm for 30 keV Ga + in Au) forcing the whole film to bend such as if it was a freestanding cantilever it will curl upwards and if it is clamped it will bow downwards.…”

Nanoscale multiply charged focused ion beam platform for surface modification, implantation, and analysis

“…Focused ion beam (FIB) is a crucial tool for the research and development of this technology, allowing elaboration, modification and characterization of material and components at the nanometric scale [1][2][3][4] . The last decade has seen the emergence and the development of new domains in nanoscience such as spintronic 5,6 , opto-electronic with the elaboration of quantum dots [7][8][9][10] and single ion implantation [11][12][13][14] . These new fields require localized implantation of elements at depths that are not commonly used in previous technology.…”

“…Liquid Metal Ion Source (LMIS) are used on conventional FIB, due to their ease of use and their outstanding brightness. Most of them are producing Ga + ions, but with the development of mass-selecting FIB, separable alloys source became more and more popular, providing access to a larger range of ion species 7,17 . Moreover, electron beam ion sources (EBIS) were tested on FIB column 18,19 , producing tens of pi-coAmp beams of multiply charged ions with diameters of a few micrometers.…”