Influencing factors on the size uniformity of self-assembled SiGe quantum rings grown by molecular beam epitaxy

Abstract

The size uniformity of self-assembled SiGe quantum rings, which are formed by capping SiGe quantum dots with a thin Si layer, is found to be greatly influenced by the growth temperature and the areal density of SiGe quantum dots. Higher growth temperature benefits the size uniformity of quantum dots, but results in low Ge concentration as well as asymmetric Ge distribution in the dots, which induces the subsequently formed quantum rings to be asymmetric in shape or even broken somewhere in the ridge of rings. Low growth temperature degrades the size uniformity of quantum dots, and thus that of quantum rings. A high areal density results in the expansion and coalescence of neighboring quantum dots to form a chain, rather than quantum rings. Uniform quantum rings with a size dispersion of 4.6% and an areal density of 7.8×10(8) cm(-2) are obtained at the optimized growth temperature of 640°C.

Ordered GeSi nanorings grown on patterned Si (001) substrates

“…A network composed of such thin layers can be seen in a large area AFM scan. In this case, QDs can scarcely transform into nanorings when a thin Si capping layer is deposited, which is similar to the case of very high QD density [23]. By using larger PS nanospheres with a diameter of 430 nm and the fabrication processes described previously, no such network was observed, and most of QDs transformed into nanorings.…”

Designer Ge/Si composite quantum dots with enhanced thermoelectric properties

“…Based on the selectivity of a H 2 O 2 -or BPAcontaining solution, that etches preferentially Ge over Si, it was possible to follow the time evolution of the etching process and to determine the spatial distribution of Si and Ge in Ge QDs with a resolution of a few nanometers. 18,[24][25][26] In this study, selective chemical etching was conducted on the CQD samples at rt to reveal their composition distributions as well as to study their formation mechanisms. A mixture of NH 4 OH, H 2 O 2 , and deionized water was used as the etchant that selectively removes Ge over Si at rt and has an extremely low etching rate for the SiGe alloy with Ge composition less than 30%.…”

Controllable growth of GeSi nanostructures by molecular beam epitaxy

“…Both ordered Ge NIs and NRs were successfully realized with the same period of 430 nm. The mechanism behind the shape transformation from Ge NIs to NRs on patterned substrate is the Ge out-diffusion and Ge-Si interdiffusion during the Si capping process at high temperatures, which is similar to that on flat Si substrate [55] . The formation of ordered Ge NRs was found to critically depend on the pattern period.…”

“…Our group has done extensive studies on the controllable growth of Ge islands on periodic patterned Si surfaces, achieving a number of ordered Ge NIs in various geometries [41,44,47,[52][53][54][55] . Ordered Ge NIs on Si surfaces with areal densities ranging from 4 × 10 5 to 1 × 10 10 cm −3 have been realized via pattern-assisted growth.…”