Ikonic, Z

Kelsall, RW

Valavanis, A

White Rose Research Online

This is a repository copy of Growth variation effects in two-dimensional Si/SiGe heterostructures.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/110098/Version: Published VersionConference or Workshop Item:Valavanis, A orcid.org/0000-0001-5565-0463, Ikonic, Z and Kelsall, RW Growth variation effects in two-dimensional Si/SiGe heterostructures. In: Photon 08, 26-29 Aug 2008, Edinburgh, UK. eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Growth variation effects in two-dimensional Si/SiGe heterostructuresA. Valavanis, Z. Ikonić and R. W. KelsallInstitute of Microwaves and Photonics,School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK2D Si/SiGe heterostructures●Potential candidates for photonic system-on-a-chip applications●Resonant tunneling diodes have been demonstrated and electroluminescence observed from quantum cascade structures●Most theoretical models assume abrupt interfaces but real interfaces may be diffuse●Annealing leads to symmetric interdiffusion, with a diffusion length L.  Similar results assumed for asymmetric surface segregation●Potentially significant effects on band structure and carrier dynamicsTheoretical approachEffect on band structure●Wavefunction overlap increases●ΔE initially increases as wells narrow but decreases as wells mergeScattering processes●Rapid alloy disorder (AD) scattering when wells contain mixture of Si and Ge●Rapid interface roughness (IR) scattering when wavefunctions overlap interfaces●Slow ionised impurity (II) and electron-electron (EE) scattering due to low doping●Inelastic electron-phonon (EP) interactions increase with subband spacing ΔE and saturate when ΔE exceeds phonon energy●All scattering processes, including elastic acoustic phonon (AC) scattering, increase with the overlap between wavefunctionsSimulated annealing calculations (n-type)(001) oriented Si-rich systemsLarge effective mass mq≈0.92me → thin layers.  Widths vary rapidly with increasing L and ΔE is strongly affected.  AD increases significantly due to Ge entering wells(111) oriented Si-rich systemsmq≈0.26me → thicker layers are relatively insensitive to L.  ΔE and scattering rates are therefore fairly stable.  AD increase partly offset by IR decrease(001) oriented Ge-rich systemsmq≈0.12me. “single well” regime does not start until L ~ 3.5nm.  Low phonon energy (ħω=28meV) leads to EP dominating when ΔE>ħω.  Other rates fairly stable in uncoupled regime.Figures of merit●Can define a set of figures of merit for tolerance to interdiffusion in the systems simulated in this work as follows:●Lpk – diffusion length resulting in maximal subband spacing.  (Ideal value = ∞)●ΔEpk – subband separation at first local maximum, relative to nominal value.  (Ideal value = 1)●LW – diffusion length yielding 50% shift in total intersubband scattering rate (Ideal value = ∞)ConclusionsSystem1.41 1.75 1.271.37 0.99 1.493.84 1.83 0.941.79 1.65 0.91Lpk (nm) ΔEpk LW (nm)n-type (001) Si-richn-type (111) Si-richn-type (001) Ge-richp-type (001) Si-rich●Interdiffusion causes large changes in transition energies and scattering rates (particularly AD in n-type structures)●Barrier degradation leads to merging of quantum wells.●Transition energy shift in Ge rich systems increases electron-phonon scattering●Scattering in p-type systems affected by change of upper subband from light-hole to heavy-hole character●n-type (111) oriented Si-rich systems yield most stable transition energy and scattering rates due to low effective mass and high phonon energiesSimulated annealing calculation (p-type)(001) oriented Si-rich systemsUpper subband is light-hole (mq≈0.16me) when weakly coupled but heavy-hole (mq≈0.49me) otherwise.  Large variation in mass  strongly affects scattering rates.TL=4K,Te=24KTL=4K,Te=24KTL=4K,Te=24KTL=4K,Te=24K

Growth variation effects in two-dimensional Si/SiGe heterostructures

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Growth variation effects in two-dimensional Si/SiGe heterostructures

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