Controlled Formation of Stacked Si Quantum Dots in Vertical SiGe Nanowires

• Published in: Nano letters 2021-10, Vol.21 (19), p.7905-7912
• Main Authors: Turner, Emily M, Campbell, Quinn, Pizarro, Joaquín, Yang, Hongbin, Sapkota, Keshab R, Lu, Ping, Baczewski, Andrew D, Wang, George T, Jones, Kevin S
• Format: Article
• Language: English
• Subjects: high-temperature oxidation; NANOSCIENCE AND NANOTECHNOLOGY; Si quantum dots; Si/SiGe pillars; vertically stacked QDs
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.1c01670

We demonstrate the ability to fabricate vertically stacked Si quantum dots (QDs) within SiGe nanowires with QD diameters down to 2 nm. These QDs are formed during high-temperature dry oxidation of Si/SiGe heterostructure pillars, during which Ge diffuses along the pillars’ sidewalls and encapsulates the Si layers. Continued oxidation results in QDs with sizes dependent on oxidation time. The formation of a Ge-rich shell that encapsulates the Si QDs is observed, a configuration which is confirmed to be thermodynamically favorable with molecular dynamics and density functional theory. The type-II band alignment of the Si dot/SiGe pillar suggests that charge trapping on the Si QDs is possible, and electron energy loss spectra show that a conduction band offset of at least 200 meV is maintained for even the smallest Si QDs. Our approach is compatible with current Si-based manufacturing processes, offering a new avenue for realizing Si QD devices.