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Constantinou P, Stock TJZ, Crane E, Kölker A, van Loon M, Li J, Fearn S, Bornemann H, D'Anna N, Fisher AJ, Strocov VN, Aeppli G, Curson NJ, Schofield SR. Momentum-Space Imaging of Ultra-Thin Electron Liquids in δ-Doped Silicon. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2302101. [PMID: 37469010 PMCID: PMC10520640 DOI: 10.1002/advs.202302101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2023] [Revised: 06/24/2023] [Indexed: 07/21/2023]
Abstract
Two-dimensional dopant layers (δ-layers) in semiconductors provide the high-mobility electron liquids (2DELs) needed for nanoscale quantum-electronic devices. Key parameters such as carrier densities, effective masses, and confinement thicknesses for 2DELs have traditionally been extracted from quantum magnetotransport. In principle, the parameters are immediately readable from the one-electron spectral function that can be measured by angle-resolved photoemission spectroscopy (ARPES). Here, buried 2DEL δ-layers in silicon are measured with soft X-ray (SX) ARPES to obtain detailed information about their filled conduction bands and extract device-relevant properties. This study takes advantage of the larger probing depth and photon energy range of SX-ARPES relative to vacuum ultraviolet (VUV) ARPES to accurately measure the δ-layer electronic confinement. The measurements are made on ambient-exposed samples and yield extremely thin (< 1 nm) and dense (≈1014 cm-2 ) 2DELs. Critically, this method is used to show that δ-layers of arsenic exhibit better electronic confinement than δ-layers of phosphorus fabricated under identical conditions.
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Affiliation(s)
- Procopios Constantinou
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Physics and AstronomyUniversity College LondonLondonWC1E 6BTUK
- Photon Science DivisionPaul Scherrer InstitutVilligen‐PSI5232Switzerland
| | - Taylor J. Z. Stock
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Electronic and Electrical EngineeringUniversity College LondonLondonWC1E 7JEUK
| | - Eleanor Crane
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Electronic and Electrical EngineeringUniversity College LondonLondonWC1E 7JEUK
| | - Alexander Kölker
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Electronic and Electrical EngineeringUniversity College LondonLondonWC1E 7JEUK
| | - Marcel van Loon
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Physics and AstronomyUniversity College LondonLondonWC1E 6BTUK
| | - Juerong Li
- Advanced Technology InstituteUniversity of SurreyGuildfordGU2 7XHUK
| | - Sarah Fearn
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of MaterialsImperial College of LondonLondonSW7 2AZUK
| | - Henric Bornemann
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Physics and AstronomyUniversity College LondonLondonWC1E 6BTUK
| | - Nicolò D'Anna
- Photon Science DivisionPaul Scherrer InstitutVilligen‐PSI5232Switzerland
| | - Andrew J. Fisher
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Physics and AstronomyUniversity College LondonLondonWC1E 6BTUK
| | | | - Gabriel Aeppli
- Photon Science DivisionPaul Scherrer InstitutVilligen‐PSI5232Switzerland
- Institute of PhysicsEcole Polytechnique Fédérale de Lausanne (EPFL)Lausanne1015Switzerland
- Department of PhysicsETH ZürichZurich8093Switzerland
- Quantum CenterEidgenössische Technische Hochschule Zurich (ETHZ)Zurich8093Switzerland
| | - Neil J. Curson
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Electronic and Electrical EngineeringUniversity College LondonLondonWC1E 7JEUK
| | - Steven R. Schofield
- London Centre for NanotechnologyUniversity College LondonLondonWC1H 0AHUK
- Department of Physics and AstronomyUniversity College LondonLondonWC1E 6BTUK
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2
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Røst HI, Tosi E, Strand FS, Åsland AC, Lacovig P, Lizzit S, Wells JW. Probing the Atomic Arrangement of Subsurface Dopants in a Silicon Quantum Device Platform. ACS APPLIED MATERIALS & INTERFACES 2023; 15:22637-22643. [PMID: 37114767 PMCID: PMC10176322 DOI: 10.1021/acsami.2c23011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
High-density structures of subsurface phosphorus dopants in silicon continue to garner interest as a silicon-based quantum computer platform; however, a much-needed confirmation of their dopant arrangement has been lacking. In this work, we take advantage of the chemical specificity of X-ray photoelectron diffraction to obtain the precise structural configuration of P dopants in subsurface Si:P δ-layers. The growth of δ-layer systems with different levels of doping is carefully studied and verified using X-ray photoelectron spectroscopy and low-energy electron diffraction. Subsequent diffraction measurements reveal that in all cases, the subsurface dopants primarily substitute with Si atoms from the host material. Furthermore, no signs of carrier-inhibiting P-P dimerization can be observed. Our observations not only settle a nearly decade-long debate about the dopant arrangement but also demonstrate how X-ray photoelectron diffraction is surprisingly well suited for studying subsurface dopant structure. This work thus provides valuable input for an updated understanding of the behavior of Si:P δ-layers and the modeling of their derived quantum devices.
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Affiliation(s)
- Håkon I Røst
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
- Department of Physics and Technology, University of Bergen (UiB), Allégaten 55, 5007 Bergen, Norway
| | - Ezequiel Tosi
- Elettra-Sincrotrone Trieste, s.s. 14-km.163,5 in Area Science Park, Basovizza, Trieste 34149, Italy
- Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) C/Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain
| | - Frode S Strand
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
| | - Anna Cecilie Åsland
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
| | - Paolo Lacovig
- Elettra-Sincrotrone Trieste, s.s. 14-km.163,5 in Area Science Park, Basovizza, Trieste 34149, Italy
| | - Silvano Lizzit
- Elettra-Sincrotrone Trieste, s.s. 14-km.163,5 in Area Science Park, Basovizza, Trieste 34149, Italy
| | - Justin W Wells
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
- Department of Physics and Centre for Materials Science and Nanotechnology, University of Oslo (UiO), Oslo 0318, Norway
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3
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Wang X, Khatami E, Fei F, Wyrick J, Namboodiri P, Kashid R, Rigosi AF, Bryant G, Silver R. Experimental realization of an extended Fermi-Hubbard model using a 2D lattice of dopant-based quantum dots. Nat Commun 2022; 13:6824. [PMID: 36369280 PMCID: PMC9652469 DOI: 10.1038/s41467-022-34220-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 10/14/2022] [Indexed: 11/13/2022] Open
Abstract
The Hubbard model is an essential tool for understanding many-body physics in condensed matter systems. Artificial lattices of dopants in silicon are a promising method for the analog quantum simulation of extended Fermi-Hubbard Hamiltonians in the strong interaction regime. However, complex atom-based device fabrication requirements have meant emulating a tunable two-dimensional Fermi-Hubbard Hamiltonian in silicon has not been achieved. Here, we fabricate 3 × 3 arrays of single/few-dopant quantum dots with finite disorder and demonstrate tuning of the electron ensemble using gates and probe the many-body states using quantum transport measurements. By controlling the lattice constants, we tune the hopping amplitude and long-range interactions and observe the finite-size analogue of a transition from metallic to Mott insulating behavior. We simulate thermally activated hopping and Hubbard band formation using increased temperatures. As atomically precise fabrication continues to improve, these results enable a new class of engineered artificial lattices to simulate interactive fermionic models. Atomically precise artificial lattices of dopant-based quantum dots offer a tunable platform for simulations of interacting fermionic models. By leveraging advances in fabrication and atomic-state control, Wang et al. report quantum simulations of the 2D Fermi-Hubbard model on a 3 × 3 few-dopant quantum dot array.
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Owen JHG, Campbell Q, Santini R, Ivie JA, Baczewski AD, Schmucker SW, Bussmann E, Misra S, Randall JN. Al-alkyls as acceptor dopant precursors for atomic-scale devices. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:464001. [PMID: 34399418 DOI: 10.1088/1361-648x/ac1ddf] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 08/16/2021] [Indexed: 06/13/2023]
Abstract
Atomically precise ultradoping of silicon is possible with atomic resists, area-selective surface chemistry, and a limited set of hydride and halide precursor molecules, in a process known as atomic precision advanced manufacturing (APAM). It is desirable to expand this set of precursors to include dopants with organic functional groups and here we consider aluminium alkyls, to expand the applicability of APAM. We explore the impurity content and selectivity that results from using trimethyl aluminium and triethyl aluminium precursors on Si(001) to ultradope with aluminium through a hydrogen mask. Comparison of the methylated and ethylated precursors helps us understand the impact of hydrocarbon ligand selection on incorporation surface chemistry. Combining scanning tunneling microscopy and density functional theory calculations, we assess the limitations of both classes of precursor and extract general principles relevant to each.
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Affiliation(s)
- J H G Owen
- Zyvex Labs, Richardson, TX, United States of America
| | - Q Campbell
- Sandia National Labs, Albuquerque, NM, United States of America
| | - R Santini
- Zyvex Labs, Richardson, TX, United States of America
| | - J A Ivie
- Sandia National Labs, Albuquerque, NM, United States of America
| | - A D Baczewski
- Sandia National Labs, Albuquerque, NM, United States of America
| | - S W Schmucker
- Sandia National Labs, Albuquerque, NM, United States of America
| | - E Bussmann
- Sandia National Labs, Albuquerque, NM, United States of America
| | - S Misra
- Sandia National Labs, Albuquerque, NM, United States of America
| | - J N Randall
- Zyvex Labs, Richardson, TX, United States of America
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5
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Valley interference and spin exchange at the atomic scale in silicon. Nat Commun 2020; 11:6124. [PMID: 33257680 PMCID: PMC7705737 DOI: 10.1038/s41467-020-19835-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 10/29/2020] [Indexed: 11/23/2022] Open
Abstract
Tunneling is a fundamental quantum process with no classical equivalent, which can compete with Coulomb interactions to give rise to complex phenomena. Phosphorus dopants in silicon can be placed with atomic precision to address the different regimes arising from this competition. However, they exploit wavefunctions relying on crystal band symmetries, which tunneling interactions are inherently sensitive to. Here we directly image lattice-aperiodic valley interference between coupled atoms in silicon using scanning tunneling microscopy. Our atomistic analysis unveils the role of envelope anisotropy, valley interference and dopant placement on the Heisenberg spin exchange interaction. We find that the exchange can become immune to valley interference by engineering in-plane dopant placement along specific crystallographic directions. A vacuum-like behaviour is recovered, where the exchange is maximised to the overlap between the donor orbitals, and pair-to-pair variations limited to a factor of less than 10 considering the accuracy in dopant positioning. This robustness remains over a large range of distances, from the strongly Coulomb interacting regime relevant for high-fidelity quantum computation to strongly coupled donor arrays of interest for quantum simulation in silicon. Coupled donor wavefunctions in silicon are spatially resolved to evidence valley interference processes. An atomic-scale understanding of the interplay between interference, envelope anisotropy and crystal symmetries unveils a placement strategy compatible with existing technology where the exchange is insensitive to interference.
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6
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Stock TJZ, Warschkow O, Constantinou PC, Li J, Fearn S, Crane E, Hofmann EVS, Kölker A, McKenzie DR, Schofield SR, Curson NJ. Atomic-Scale Patterning of Arsenic in Silicon by Scanning Tunneling Microscopy. ACS NANO 2020; 14:3316-3327. [PMID: 32142256 PMCID: PMC7146850 DOI: 10.1021/acsnano.9b08943] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Over the past two decades, prototype devices for future classical and quantum computing technologies have been fabricated by using scanning tunneling microscopy and hydrogen resist lithography to position phosphorus atoms in silicon with atomic-scale precision. Despite these successes, phosphine remains the only donor precursor molecule to have been demonstrated as compatible with the hydrogen resist lithography technique. The potential benefits of atomic-scale placement of alternative dopant species have, until now, remained unexplored. In this work, we demonstrate the successful fabrication of atomic-scale structures of arsenic-in-silicon. Using a scanning tunneling microscope tip, we pattern a monolayer hydrogen mask to selectively place arsenic atoms on the Si(001) surface using arsine as the precursor molecule. We fully elucidate the surface chemistry and reaction pathways of arsine on Si(001), revealing significant differences to phosphine. We explain how these differences result in enhanced surface immobilization and in-plane confinement of arsenic compared to phosphorus, and a dose-rate independent arsenic saturation density of 0.24 ± 0.04 monolayers. We demonstrate the successful encapsulation of arsenic delta-layers using silicon molecular beam epitaxy, and find electrical characteristics that are competitive with equivalent structures fabricated with phosphorus. Arsenic delta-layers are also found to offer confinement as good as similarly prepared phosphorus layers, while still retaining >80% carrier activation and sheet resistances of <2 kΩ/square. These excellent characteristics of arsenic represent opportunities to enhance existing capabilities of atomic-scale fabrication of dopant structures in silicon, and may be important for three-dimensional devices, where vertical control of the position of device components is critical.
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Affiliation(s)
- Taylor J. Z. Stock
- London
Centre for Nanotechnology, University College
London, London WC1H 0AH, U.K.
| | - Oliver Warschkow
- Centre
for Quantum Computation and Communication Technology, School of Physics, The University of Sydney, Sydney, NSW 2006, Australia
| | | | - Juerong Li
- Advanced
Technology Institute, University of Surrey, Guildford GU2 7XH, U.K.
| | - Sarah Fearn
- London
Centre for Nanotechnology, University College
London, London WC1H 0AH, U.K.
- Department
of Materials, Imperial College of London, London SW7 2AZ, U.K.
| | - Eleanor Crane
- London
Centre for Nanotechnology, University College
London, London WC1H 0AH, U.K.
| | - Emily V. S. Hofmann
- London
Centre for Nanotechnology, University College
London, London WC1H 0AH, U.K.
- IHP
− Leibniz-Institut für Innovative Mikroelektronik, Frankfurt (Oder) 15236, Germany
| | - Alexander Kölker
- London
Centre for Nanotechnology, University College
London, London WC1H 0AH, U.K.
| | - David R. McKenzie
- Centre
for Quantum Computation and Communication Technology, School of Physics, The University of Sydney, Sydney, NSW 2006, Australia
| | - Steven R. Schofield
- London
Centre for Nanotechnology, University College
London, London WC1H 0AH, U.K.
- Department
of Physics and Astronomy, University College
London, London WC1E 6BT, U.K.
| | - Neil J. Curson
- London
Centre for Nanotechnology, University College
London, London WC1H 0AH, U.K.
- Department
of Electronic and Electrical Engineering, University College London, London WC1E 7JE, U.K.
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7
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Schmucker SW, Namboodiri PN, Kashid R, Wang X, Hu B, Wyrick JE, Myers AF, Schumacher JD, Silver RM, Stewart MD. Low-Resistance, High-Yield Electrical Contacts to Atom Scale Si:P Devices Using Palladium Silicide. PHYSICAL REVIEW APPLIED 2019; 11:10.1103/PhysRevApplied.11.034071. [PMID: 31579257 PMCID: PMC6774366 DOI: 10.1103/physrevapplied.11.034071] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Scanning tunneling microscopy (STM) enables the fabrication of two-dimensional δ-doped structures in Si with atomistic precision, with applications from tunnel field-effect transistors to qubits. The combination of a very small contact area and the restrictive thermal budget necessary to maintain the integrity of the δ layer make developing a robust electrical contact method a significant challenge to realizing the potential of atomically precise devices. We demonstrate a method for electrical contact using Pd2Si formed at the temperature of silicon overgrowth (250 °C), minimizing the diffusive impact on the δ layer. We use the transfer length method to show our Pd2Si contacts have very high yield (99.7% +0.2% -1.5%) and low resistivity (272±41Ωμm) in contacting mesa-etched Si:P δ layers. We also present three terminal measurements of low contact resistance (<1 kΩ) to devices written by STM hydrogen depassivation lithography with similarly high yield (100% +0% -3.2%).
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Affiliation(s)
| | | | - Ranjit Kashid
- National Institute of Standards & Technology, Gaithersburg, Maryland 20899, USA
| | - Xiqiao Wang
- University of Maryland, College Park, Maryland 20742, USA
| | - Binhui Hu
- University of Maryland, College Park, Maryland 20742, USA
| | - Jonathan E. Wyrick
- National Institute of Standards & Technology, Gaithersburg, Maryland 20899, USA
| | - Alline F. Myers
- National Institute of Standards & Technology, Gaithersburg, Maryland 20899, USA
| | | | - Richard M. Silver
- National Institute of Standards & Technology, Gaithersburg, Maryland 20899, USA
| | - M. D. Stewart
- National Institute of Standards & Technology, Gaithersburg, Maryland 20899, USA
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