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Nanomembrane-based materials for Group IV semiconductor quantum electronics.

Paskiewicz DM, Savage DE, Holt MV, Evans PG, Lagally MG - Sci Rep (2014)

Bottom Line: Strained-silicon/relaxed-silicon-germanium alloy (strained-Si/SiGe) heterostructures are the foundation of Group IV-element quantum electronics and quantum computation, but current materials quality limits the reliability and thus the achievable performance of devices.Because the nanomembrane is truly a single crystal, in contrast to the conventional SiGe substrate made by compositionally grading SiGe grown on bulk Si, significant improvements in quantum electronic-device reliability may be expected with nanomembrane substrates.Significant structural improvements are found using SiGe nanomembranes.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Materials Science & Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 USA [2].

ABSTRACT
Strained-silicon/relaxed-silicon-germanium alloy (strained-Si/SiGe) heterostructures are the foundation of Group IV-element quantum electronics and quantum computation, but current materials quality limits the reliability and thus the achievable performance of devices. In comparison to conventional approaches, single-crystal SiGe nanomembranes are a promising alternative as substrates for the epitaxial growth of these heterostructures. Because the nanomembrane is truly a single crystal, in contrast to the conventional SiGe substrate made by compositionally grading SiGe grown on bulk Si, significant improvements in quantum electronic-device reliability may be expected with nanomembrane substrates. We compare lateral strain inhomogeneities and the local mosaic structure (crystalline tilt) in strained-Si/SiGe heterostructures that we grow on SiGe nanomembranes and on compositionally graded SiGe substrates, with micro-Raman mapping and nanodiffraction, respectively. Significant structural improvements are found using SiGe nanomembranes.

No MeSH data available.


Related in: MedlinePlus

Schematic diagrams of fabrication processes for conventional compositionally graded, plastically relaxed SiGe substrates and the new elastically relaxed SiGe NMs.(a) Conventional approach: i. The initial, low-Ge-composition Si1−aGea is strained to the Si lattice constant. ii. As the total SiGe alloy thickness and Ge composition increases (c > b > a), the SiGe begins to relax via misfit dislocations. iii. The alloy composition can be step graded or continuously graded (typically ~10%/μm) until the desired Ge composition is reached and the alloy is fully relaxed. iv. The relaxed graded substrate is then chemically-mechanically polished before epitaxial growth of a constant-composition, lattice-matched Si1−xGex buffer layer and the strained-Si QW. (b) New NM process: i. A thin Si1−xGex layer is epitaxially grown on a silicon-on-insulator (SOI) substrate followed by a Si capping layer similar in thickness to the Si template layer of the SOI. The Si1−xGex layer is strained to the Si lattice constant. ii. The trilayer Si/SiGe/Si heterostructure is released from the original Si substrate by selectively etching away the SiO2 layer. The trilayer is allowed to strain share: some of the compressive strain in the SiGe layer is transferred as tensile strain to the outer Si layers. iii. The outer Si layers are selectively etched away. Removing the outer layers allows the Si1−xGex NM to relax elastically to the bulk lattice constant appropriate for the alloy composition. iv. The SiGe NM is transferred to a new host substrate (in this work an oxidized Si wafer) and bonded there before a lattice matched SiGe buffer layer and strained-Si QW are epitaxially grown on top.
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f1: Schematic diagrams of fabrication processes for conventional compositionally graded, plastically relaxed SiGe substrates and the new elastically relaxed SiGe NMs.(a) Conventional approach: i. The initial, low-Ge-composition Si1−aGea is strained to the Si lattice constant. ii. As the total SiGe alloy thickness and Ge composition increases (c > b > a), the SiGe begins to relax via misfit dislocations. iii. The alloy composition can be step graded or continuously graded (typically ~10%/μm) until the desired Ge composition is reached and the alloy is fully relaxed. iv. The relaxed graded substrate is then chemically-mechanically polished before epitaxial growth of a constant-composition, lattice-matched Si1−xGex buffer layer and the strained-Si QW. (b) New NM process: i. A thin Si1−xGex layer is epitaxially grown on a silicon-on-insulator (SOI) substrate followed by a Si capping layer similar in thickness to the Si template layer of the SOI. The Si1−xGex layer is strained to the Si lattice constant. ii. The trilayer Si/SiGe/Si heterostructure is released from the original Si substrate by selectively etching away the SiO2 layer. The trilayer is allowed to strain share: some of the compressive strain in the SiGe layer is transferred as tensile strain to the outer Si layers. iii. The outer Si layers are selectively etched away. Removing the outer layers allows the Si1−xGex NM to relax elastically to the bulk lattice constant appropriate for the alloy composition. iv. The SiGe NM is transferred to a new host substrate (in this work an oxidized Si wafer) and bonded there before a lattice matched SiGe buffer layer and strained-Si QW are epitaxially grown on top.

Mentions: Conventionally, strained-Si QWs are epitaxially (pseudomorphically) grown on thick, compositionally graded, plastically strain relaxed (i.e., irreversible reduction in strain) SiGe films grown on Si substrates11 (Figure 1a). Plastic strain relaxation occurs via a network of buried misfit dislocations (Figure 1a-iii.). A non-uniform distribution of misfit dislocations in the compositionally graded, plastically relaxed SiGe substrate will result in a non-uniform strain distribution in the epitaxial strained-Si layer grown on top1213. Additionally, the nature of the plastic relaxation results in crystallites that have small misorientations with respect to each other, called crystalline tilt or mosaic structure, in the SiGe substrate14 that is also transferred to the strained-Si QW15. These structural imperfections can result in changes in the conduction band offsets between Si and SiGe (caused by strain variations) and charge carrier scattering from rough interfaces and crystalline imperfections (caused by mosaic structure); both effects contribute to the inconsistencies in the performance of quantum electronic devices described above.


Nanomembrane-based materials for Group IV semiconductor quantum electronics.

Paskiewicz DM, Savage DE, Holt MV, Evans PG, Lagally MG - Sci Rep (2014)

Schematic diagrams of fabrication processes for conventional compositionally graded, plastically relaxed SiGe substrates and the new elastically relaxed SiGe NMs.(a) Conventional approach: i. The initial, low-Ge-composition Si1−aGea is strained to the Si lattice constant. ii. As the total SiGe alloy thickness and Ge composition increases (c > b > a), the SiGe begins to relax via misfit dislocations. iii. The alloy composition can be step graded or continuously graded (typically ~10%/μm) until the desired Ge composition is reached and the alloy is fully relaxed. iv. The relaxed graded substrate is then chemically-mechanically polished before epitaxial growth of a constant-composition, lattice-matched Si1−xGex buffer layer and the strained-Si QW. (b) New NM process: i. A thin Si1−xGex layer is epitaxially grown on a silicon-on-insulator (SOI) substrate followed by a Si capping layer similar in thickness to the Si template layer of the SOI. The Si1−xGex layer is strained to the Si lattice constant. ii. The trilayer Si/SiGe/Si heterostructure is released from the original Si substrate by selectively etching away the SiO2 layer. The trilayer is allowed to strain share: some of the compressive strain in the SiGe layer is transferred as tensile strain to the outer Si layers. iii. The outer Si layers are selectively etched away. Removing the outer layers allows the Si1−xGex NM to relax elastically to the bulk lattice constant appropriate for the alloy composition. iv. The SiGe NM is transferred to a new host substrate (in this work an oxidized Si wafer) and bonded there before a lattice matched SiGe buffer layer and strained-Si QW are epitaxially grown on top.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3936214&req=5

f1: Schematic diagrams of fabrication processes for conventional compositionally graded, plastically relaxed SiGe substrates and the new elastically relaxed SiGe NMs.(a) Conventional approach: i. The initial, low-Ge-composition Si1−aGea is strained to the Si lattice constant. ii. As the total SiGe alloy thickness and Ge composition increases (c > b > a), the SiGe begins to relax via misfit dislocations. iii. The alloy composition can be step graded or continuously graded (typically ~10%/μm) until the desired Ge composition is reached and the alloy is fully relaxed. iv. The relaxed graded substrate is then chemically-mechanically polished before epitaxial growth of a constant-composition, lattice-matched Si1−xGex buffer layer and the strained-Si QW. (b) New NM process: i. A thin Si1−xGex layer is epitaxially grown on a silicon-on-insulator (SOI) substrate followed by a Si capping layer similar in thickness to the Si template layer of the SOI. The Si1−xGex layer is strained to the Si lattice constant. ii. The trilayer Si/SiGe/Si heterostructure is released from the original Si substrate by selectively etching away the SiO2 layer. The trilayer is allowed to strain share: some of the compressive strain in the SiGe layer is transferred as tensile strain to the outer Si layers. iii. The outer Si layers are selectively etched away. Removing the outer layers allows the Si1−xGex NM to relax elastically to the bulk lattice constant appropriate for the alloy composition. iv. The SiGe NM is transferred to a new host substrate (in this work an oxidized Si wafer) and bonded there before a lattice matched SiGe buffer layer and strained-Si QW are epitaxially grown on top.
Mentions: Conventionally, strained-Si QWs are epitaxially (pseudomorphically) grown on thick, compositionally graded, plastically strain relaxed (i.e., irreversible reduction in strain) SiGe films grown on Si substrates11 (Figure 1a). Plastic strain relaxation occurs via a network of buried misfit dislocations (Figure 1a-iii.). A non-uniform distribution of misfit dislocations in the compositionally graded, plastically relaxed SiGe substrate will result in a non-uniform strain distribution in the epitaxial strained-Si layer grown on top1213. Additionally, the nature of the plastic relaxation results in crystallites that have small misorientations with respect to each other, called crystalline tilt or mosaic structure, in the SiGe substrate14 that is also transferred to the strained-Si QW15. These structural imperfections can result in changes in the conduction band offsets between Si and SiGe (caused by strain variations) and charge carrier scattering from rough interfaces and crystalline imperfections (caused by mosaic structure); both effects contribute to the inconsistencies in the performance of quantum electronic devices described above.

Bottom Line: Strained-silicon/relaxed-silicon-germanium alloy (strained-Si/SiGe) heterostructures are the foundation of Group IV-element quantum electronics and quantum computation, but current materials quality limits the reliability and thus the achievable performance of devices.Because the nanomembrane is truly a single crystal, in contrast to the conventional SiGe substrate made by compositionally grading SiGe grown on bulk Si, significant improvements in quantum electronic-device reliability may be expected with nanomembrane substrates.Significant structural improvements are found using SiGe nanomembranes.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Materials Science & Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 USA [2].

ABSTRACT
Strained-silicon/relaxed-silicon-germanium alloy (strained-Si/SiGe) heterostructures are the foundation of Group IV-element quantum electronics and quantum computation, but current materials quality limits the reliability and thus the achievable performance of devices. In comparison to conventional approaches, single-crystal SiGe nanomembranes are a promising alternative as substrates for the epitaxial growth of these heterostructures. Because the nanomembrane is truly a single crystal, in contrast to the conventional SiGe substrate made by compositionally grading SiGe grown on bulk Si, significant improvements in quantum electronic-device reliability may be expected with nanomembrane substrates. We compare lateral strain inhomogeneities and the local mosaic structure (crystalline tilt) in strained-Si/SiGe heterostructures that we grow on SiGe nanomembranes and on compositionally graded SiGe substrates, with micro-Raman mapping and nanodiffraction, respectively. Significant structural improvements are found using SiGe nanomembranes.

No MeSH data available.


Related in: MedlinePlus