1. Yingjie Ma, Jian Cui*, Yongliang Fan, Zhenyang Zhong, Zuimin Jiang
Ordered GeSi quantum rings grown on patterned Si (001) substrates
Yingjie Ma, Jian Cui*, Yongliang Fan, Zhenyang Zhong, Zuimin Jiang
Ordered silicon-based nanostructures have attracted considerable attentions due to their unique properties and potential applications in various novel devices including field-emission displays, nanoelectronic and nanophotonic devices. It is convenient to use nanosphere lithography (NSL) technology to fabricate periodic patterns for it is cheap but effective. NSL has been used to fabricate periodic SiGe quantum dots (QDs) with the period down to 100 nm. Self-assembled quantum ring (QR) is a kind of newly discovered nanostructures. The special topological configuration has shown interesting quantum effects, e. g. persistent current in normal metal rings. In this report, we will present highly ordered GeSi QRs in large areas grown on patterned Si (001) substrates by molecular beam epitaxial.
I Pattern preparation
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The inverted pyramid-like pits arranged in a hexagonal lattice on Si (001) substrates were fabricated by reactive iron etching (RIE) and NSL technology. The schematic representation of the pattern fabrication process was shown in the left picture. After the hexagonal PS pattern was formed (Fig. 1 (a)), the pattern was etched by RIE to shrink the coverage of PS (Fig. 1 (b)). This step is necessary to the subsequent formation of QRs, because the large distance between QDs ensures the independent development of QRs when capping. The ordered inverted pyramid-like pits were obtained by selective etching of Si in KOH solution, as shown in Fig.1 (c). Then, the highly ordered inverted pyramid-like pits pattern was formed.
FIG. 1 AFM image of (a) PS pattern, (b) RIE processed pattern, (c) KOH selectively etched pattern
II Ordered QRs arrays grown by MBE
III Conclusion
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The size and shape of rings was closely associated with the size of capped GeSi QDs and the Si capping process.
Parameters including the size of PS nanospheres, RIE processing parameters, growth temperature and thickness can be adjusted and optimized to control the size and periods of QRs.
These ordered GeSi QRs may have unique electronic properties.
The ordered GeSi QRs were then grown via a two-step process. First, ordered dome shaped GeSi QDs were grown on the patterned substrates at 610 °C, as shown in Fig. 2 (a). Second, a thin Si capping layer was deposited at 610°C. By controlling the amount of deposited Si, the GeSi QDs transform into GeSi QRs . Highly ordered GeSi QRs arrays were formed, as shown in Fig. 2 (b).