Interfacial sharpness and intermixing in a Ge-SiGe multiple quantum well structure

Bashir, A. et al. (2018) Interfacial sharpness and intermixing in a Ge-SiGe multiple quantum well structure. Journal of Applied Physics, 123(3), 035703. (doi: 10.1063/1.5001158)

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A Ge-SiGe multiple quantum well structure created by low energy plasma enhanced chemical vapour deposition, with nominal well thickness of 5.4 nm separated by 3.6 nm SiGe spacers, is analysed quantitatively using scanning transmission electron microscopy. Both high angle annular dark field imaging and electron energy loss spectroscopy show that the interfaces are not completely sharp, suggesting that there is some intermixing of Si and Ge at each interface. Two methods are compared for the quantification of the spectroscopy datasets: a self-consistent approach that calculates binary substitutional trends without requiring experimental or computational k-factors from elsewhere and a standards-based cross sectional calculation. Whilst the cross section approach is shown to be ultimately more reliable, the self-consistent approach provides surprisingly good results. It is found that the Ge quantum wells are actually about 95% Ge and that the spacers, whilst apparently peaking at about 35% Si, contain significant interdiffused Ge at each side. This result is shown to be not just an artefact of electron beam spreading in the sample, but mostly arising from a real chemical interdiffusion resulting from the growth. Similar results are found by use of X-ray diffraction from a similar area of the sample. Putting the results together suggests a real interdiffusion with a standard deviation of about 0.87 nm, or put another way—a true width defined from 10%–90% of the compositional gradient of about 2.9 nm. This suggests an intrinsic limit on how sharp such interfaces can be grown by this method and, whilst 95% Ge quantum wells (QWs) still behave well enough to have good properties, any attempt to grow thinner QWs would require modifications to the growth procedure to reduce this interdiffusion, in order to maintain a composition of ≥95% Ge.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Paul, Professor Douglas and Millar, Dr Ross and MacLaren, Dr Ian and Bashir, Ms Aneeqa and Gallacher, Dr Kevin
Authors: Bashir, A., Gallacher, K., Millar, R.W., Paul, D.J., Ballabio, A., Frigerio, J., Isella, G., Kriegner, D., Ortolani, M., Barthel, J., and MacLaren, I.
College/School:College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
College of Science and Engineering > School of Physics and Astronomy
Journal Name:Journal of Applied Physics
Publisher:American Institute of Physics
ISSN (Online):1089-7550
Published Online:19 January 2018
Copyright Holders:Copyright © 2018 AIP Publishing
First Published:First published in Journal of Applied Physics 123(3):035703
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
694301Engineering Quantum Technology Systems on a Silicon PlatformDouglas PaulEngineering and Physical Sciences Research Council (EPSRC)EP/N003225/1ENG - ENGINEERING ELECTRONICS & NANO ENG