Controlled Formation of Stacked Si Quantum Dots in Vertical SiGe Nanowires

Turner, Emily M.; Campbell, Quinn; Pizarro, J.; Yang, Hongbin; Sapkota, Keshab R.; Lu, Ping; Baczewski, Andrew David; Wang, George T.; Jones, K. S.

doi:10.1021/acs.nanolett.1c01670

Cited by 6 publications

(12 citation statements)

References 64 publications

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“…The defects observed in this work are found in SiGe nanopillars formed by oxidation of Si/SiGe superlattices that are patterned into cylindrical rods [30]. Oxidations were done under dry O 2 at 900 • C for 20 minutes.…”

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confidence: 91%

Humble planar defects in SiGe nanopillars

Yang,

Ren,

Singh

et al. 2021

Preprint

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We report a new {001} planar defect found in SiGe nanopillars. The defect structure, determined by atomic resolution electron microscopy, matches the Humble defect model proposed for diamond. We also investigated several possible variants of the Humble structure using first principles calculations and found that the one lowest in energy was also in best agreement with the STEM images. The pillar composition has been analyzed with electron energy loss spectroscopy, which hints at how the defect is formed. Our results show that the structure and formation process of defects in nanostructured group IV semiconductors can be different from their bulk counterparts.

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confidence: 91%

Humble planar defects in SiGe nanopillars

Yang,

Ren,

Singh

et al. 2021

Preprint

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“…The unique diffusion of Ge during the oxidation of both poly crystalline SiGe − and single-crystal SiGe , has been the subject of many recent studies. In the oxidation of poly crystalline SiGe nanostructures, Ge diffuses rapidly via grain boundaries to the center of the structure, leading to the formation of Ge nanocrystallites. , However, for a single-crystal SiGe/Si multilayered nanofin, much like those formed during GAA processing, Brewer et al reported a novel Ge diffusion process that resulted in vertically stacked, strained, Si nanowires encapsulated in SiGe during high temperature oxidation .…”

Section: Introductionmentioning

confidence: 99%

“…In the oxidation of poly crystalline SiGe nanostructures, Ge diffuses rapidly via grain boundaries to the center of the structure, leading to the formation of Ge nanocrystallites. , However, for a single-crystal SiGe/Si multilayered nanofin, much like those formed during GAA processing, Brewer et al reported a novel Ge diffusion process that resulted in vertically stacked, strained, Si nanowires encapsulated in SiGe during high temperature oxidation . This approach was later extended to create embedded, stacked Si quantum dots encapsulated in SiGe nanopillars …”

Section: Introductionmentioning

confidence: 99%

“…This process results in Ge condensation near the SiGe/SiO 2 interface, characterized by an enhanced Ge concentration. − The concentration of Ge within the condensed SiGe region depends on the oxidizing temperature. , Once this concentration of Ge is formed near the oxidizing interface, the overall layer thickness grows approximately linearly with oxidation thickness as the Si continues to be selectively oxidized . A sharp concentration gradient remains between the region of condensed Ge and the original SiGe region because Si–Ge interdiffusion is exponentially proportional to the Ge content. , Third, Brewer et al reported that there is an additional, rapid movement of Ge down the oxidizing sidewall of the nanofin. , This diffusion of Ge seemed to be significantly faster than the reported diffusion of Ge in Si and Si 0.7 Ge 0.3 . , Therefore, the observed Ge diffusion is expected to be occurring through a novel mechanism.…”

Section: Introductionmentioning

confidence: 99%

“…The number of stacked wires formed depends on the number of Si/SiGe layers that are grown. Turner et al also used this approach to create stacked Si QDs in SiGe nanopillars with QD diameters down to 2 nm . While these results offer an exciting potential pathway to next-generation microelectronic structures and other device applications, little is known about the mechanism behind this unique, rapid diffusion of Ge vertically, down the sidewalls of Si/SiGe fins and pillars or its insertion into the Si lattice, converting a Si region into SiGe.…”

Section: Introductionmentioning

confidence: 99%

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The Diffusion Mechanism of Ge During Oxidation of Si/SiGe Nanofins

Thornton

Tuttle

Turner

et al. 2022

ACS Appl. Mater. Interfaces

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A recently discovered, enhanced Ge diffusion mechanism along the oxidizing interface of Si/SiGe nanostructures has enabled the formation of single-crystal Si nanowires and quantum dots embedded in a defect-free, single-crystal SiGe matrix. Here, we report oxidation studies of Si/SiGe nanofins aimed at gaining a better understanding of this novel diffusion mechanism. A superlattice of alternating Si/Si 0.7 Ge 0.3 layers was grown and patterned into fins. After oxidation of the fins, the rate of Ge diffusion down the Si/SiO 2 interface was measured through the analysis of HAADF-STEM images. The activation energy for the diffusion of Ge down the sidewall was found to be 1.1 eV, which is less than one-quarter of the activation energy previously reported for Ge diffusion in bulk Si. Through a combination of experiments and DFT calculations, we propose that the redistribution of Ge occurs by diffusion along the Si/SiO 2 interface followed by a reintroduction into substitutional positions in the crystalline Si.

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Selective amorphization of SiGe in Si/SiGe nanostructures via high energy Si+ implant

Turner

Campbell

Avci

et al. 2022

Journal of Applied Physics

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The selective amorphization of SiGe in Si/SiGe nanostructures via a 1 MeV Si+ implant was investigated, resulting in single-crystal Si nanowires (NWs) and quantum dots (QDs) encapsulated in amorphous SiGe fins and pillars, respectively. The Si NWs and QDs are formed during high-temperature dry oxidation of single-crystal Si/SiGe heterostructure fins and pillars, during which Ge diffuses along the nanostructure sidewalls and encapsulates the Si layers. The fins and pillars were then subjected to a 3 × 1015 ions/cm2 1 MeV Si+ implant, resulting in the amorphization of SiGe, while leaving the encapsulated Si crystalline for larger, 65-nm wide NWs and QDs. Interestingly, the 26-nm diameter Si QDs amorphize, while the 28-nm wide NWs remain crystalline during the same high energy ion implant. This result suggests that the Si/SiGe pillars have a lower threshold for Si-induced amorphization compared to their Si/SiGe fin counterparts. However, Monte Carlo simulations of ion implantation into the Si/SiGe nanostructures reveal similar predicted levels of displacements per cm3. Molecular dynamics simulations suggest that the total stress magnitude in Si QDs encapsulated in crystalline SiGe is higher than the total stress magnitude in Si NWs, which may lead to greater crystalline instability in the QDs during ion implant. The potential lower amorphization threshold of QDs compared to NWs is of special importance to applications that require robust QD devices in a variety of radiation environments.

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Controlled Formation of Stacked Si Quantum Dots in Vertical SiGe Nanowires

Cited by 6 publications

References 64 publications

Humble planar defects in SiGe nanopillars

Humble planar defects in SiGe nanopillars

The Diffusion Mechanism of Ge During Oxidation of Si/SiGe Nanofins

Selective amorphization of SiGe in Si/SiGe nanostructures via high energy Si+ implant

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