Spontaneous and assisted self-assembling of Si- and SiGe-based dielectric Mie resonators

Silicon-based nanocrystals represent a promising resource both for next-generation electronic devices and for nano-photonics applications but require precise size, shape and position control. In this seminar I will discuss the fabrication of Si- and SiGe-based nanocrystals by templated solid-state dewetting of thin silicon films (SOI) and their use in silicon photonics as dielectric Mie resonators [1,2,3]. Islands formation, organization, positioning and composition were studied by dark-field, atomic force and transmission electron microscopy. I will show the capabilities of this top-down/bottom-up hybrid method in engineering the SOI dewetting fronts thus organizing the nanocrystals in assemblies much more complex than the original etched pattern. In optimised conditions the shape of the islands, their number and their relative position can be controlled with a precision of better than 10%. Furthermore, I will show the dramatic effects of germanium alloying leading to a collapse in the number of nucleated islands and to the onset of puzzling bimodal size distributions of ordered nanocrystals.
This mask-less templating method avoids chemical etching or pattern transfer steps and paves the way for the exploitation of solid-state dewetting for the implementation of complex dielectric oligomers for silicon photonics. Our findings [2,3], open new ways of playing with ordered and disordered metamaterials for thin-film anti-reflection coating and broad-band and wide angle light-coupling [1].

M Abarchi

Figure 1. a) and b) Optical dark-field (top panels) and AFM (bottom panels) examples of complex islands arrangements obtained by solid state dewetting of patterned substrates. The etched patterns are highlighted. c) Height profiles of the islands shown in b) (right and left column (RC, LC) and bottom and top lines (BL, TL) profiles are shown from the top to the bottom panels). d) Statistical distributions of the main morphological parameters of 3 identical patterns (islands volume, perimeter, height, distance between islands and distance from the center are shown form the bottom to the top panels).

 

[1] Spinelli et al., Nat. Comm. 3, 692 (2012)
[2] M. Abbarchi et al., ACS Nano 8, 11181 (2014)
[3] M. Naffouti et al., Nanoscale 8, 7768 (2016).

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