SiGe Quantum Rings by Ultra-high Vacuum Chemical Vapor Deposition

Abstract

SiGe quanrum rings (QRs) grown at 500oC and 600oC were observed on SiGe quantum dots (QDs) capped with Si. Average depth and diameter are 9 nm and 185 nm, respectively, for QRs at 500oC, while those are 0.9 nm and 84 nm for QRs at 600oC. Ge out-diffusion mechanism is proposed to be responsible for nanorings formation in 500oC, and Si surface diffusion toward strain-free edges is proposed to be responsible for nanorings formation in 600oC. Raman spectroscopy demonstrates that formation of QRs in 600oC is close correlated with a strain-driven process. QRs grown in 600oC are the metastable states and can be only observed in very limited conditions. Thick cap and high thermal budget can both destroy SiGe nanorings structures.