1
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Tranter A, Kranz L, Sutherland S, Keizer JG, Gorman SK, Buchler BC, Simmons MY. Machine Learning-Assisted Precision Manufacturing of Atom Qubits in Silicon. ACS NANO 2024; 18. [PMID: 39018335 PMCID: PMC11295186 DOI: 10.1021/acsnano.4c00080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Revised: 06/10/2024] [Accepted: 06/13/2024] [Indexed: 07/19/2024]
Abstract
Donor-based qubits in silicon, manufactured using scanning tunneling microscope (STM) lithography, provide a promising route to realizing full-scale quantum computing architectures. This is due to the precision of donor placement, long coherence times, and scalability of the silicon material platform. The properties of multiatom quantum dot qubits, however, depend on the exact number and location of the donor atoms within the quantum dots. In this work, we develop machine learning techniques that allow accurate and real-time prediction of the donor number at the qubit site during STM patterning. Machine learning image recognition is used to determine the probability distribution of donor numbers at the qubit site directly from STM images during device manufacturing. Models in excess of 90% accuracy are found to be consistently achieved by mitigating overfitting through reduced model complexity, image preprocessing, data augmentation, and examination of the intermediate layers of the convolutional neural networks. The results presented in this paper constitute an important milestone in automating the manufacture of atom-based qubits for computation and sensing applications.
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Affiliation(s)
- Aaron
D. Tranter
- Centre
of Excellence for Quantum Computation and Communication Technology,
Department of Quantum Science and Technology, Research School of Physics, The Australian National University, Acton 2601, Australia
| | - Ludwik Kranz
- Centre
of Excellence for Quantum Computation and Communication Technology,
School of Physics, UNSW Sydney, Kensington 2052, New South Wales, Australia
- Silicon
Quantum Computing Pty Ltd, UNSW Sydney, Kensington 2052, New South Wales, Australia
| | - Sam Sutherland
- Centre
of Excellence for Quantum Computation and Communication Technology,
School of Physics, UNSW Sydney, Kensington 2052, New South Wales, Australia
- Silicon
Quantum Computing Pty Ltd, UNSW Sydney, Kensington 2052, New South Wales, Australia
| | - Joris G. Keizer
- Centre
of Excellence for Quantum Computation and Communication Technology,
School of Physics, UNSW Sydney, Kensington 2052, New South Wales, Australia
- Silicon
Quantum Computing Pty Ltd, UNSW Sydney, Kensington 2052, New South Wales, Australia
| | - Samuel K. Gorman
- Centre
of Excellence for Quantum Computation and Communication Technology,
School of Physics, UNSW Sydney, Kensington 2052, New South Wales, Australia
- Silicon
Quantum Computing Pty Ltd, UNSW Sydney, Kensington 2052, New South Wales, Australia
| | - Benjamin C. Buchler
- Centre
of Excellence for Quantum Computation and Communication Technology,
Department of Quantum Science and Technology, Research School of Physics, The Australian National University, Acton 2601, Australia
| | - Michelle Y. Simmons
- Centre
of Excellence for Quantum Computation and Communication Technology,
School of Physics, UNSW Sydney, Kensington 2052, New South Wales, Australia
- Silicon
Quantum Computing Pty Ltd, UNSW Sydney, Kensington 2052, New South Wales, Australia
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2
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Stock TJZ, Warschkow O, Constantinou PC, Bowler DR, Schofield SR, Curson NJ. Single-Atom Control of Arsenic Incorporation in Silicon for High-Yield Artificial Lattice Fabrication. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2312282. [PMID: 38380859 DOI: 10.1002/adma.202312282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 01/29/2024] [Indexed: 02/22/2024]
Abstract
Artificial lattices constructed from individual dopant atoms within a semiconductor crystal hold promise to provide novel materials with tailored electronic, magnetic, and optical properties. These custom-engineered lattices are anticipated to enable new, fundamental discoveries in condensed matter physics and lead to the creation of new semiconductor technologies including analog quantum simulators and universal solid-state quantum computers. This work reports precise and repeatable, substitutional incorporation of single arsenic atoms into a silicon lattice. A combination of scanning tunneling microscopy hydrogen resist lithography and a detailed statistical exploration of the chemistry of arsine on the hydrogen-terminated silicon (001) surface are employed to show that single arsenic dopants can be deterministically placed within four silicon lattice sites and incorporated with 97 ± 2% yield. These findings bring closer to the ultimate frontier in semiconductor technology: the deterministic assembly of atomically precise dopant and qubit arrays at arbitrarily large scales.
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Affiliation(s)
- Taylor J Z Stock
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, UK
- Department of Electronic and Electrical Engineering, University College London, London, WC1E 7JE, UK
| | - Oliver Warschkow
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, UK
| | - Procopios C Constantinou
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, UK
| | - David R Bowler
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, UK
- Department of Physics and Astronomy, University College London, London, WC1E 6BT, UK
| | - Steven R Schofield
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, UK
- Department of Physics and Astronomy, University College London, London, WC1E 6BT, UK
| | - Neil J Curson
- London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, UK
- Department of Electronic and Electrical Engineering, University College London, London, WC1E 7JE, UK
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3
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Pitters J, Croshaw J, Achal R, Livadaru L, Ng S, Lupoiu R, Chutora T, Huff T, Walus K, Wolkow RA. Atomically Precise Manufacturing of Silicon Electronics. ACS NANO 2024; 18:6766-6816. [PMID: 38376086 PMCID: PMC10919096 DOI: 10.1021/acsnano.3c10412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 02/01/2024] [Accepted: 02/06/2024] [Indexed: 02/21/2024]
Abstract
Atomically precise manufacturing (APM) is a key technique that involves the direct control of atoms in order to manufacture products or components of products. It has been developed most successfully using scanning probe methods and has received particular attention for developing atom scale electronics with a focus on silicon-based systems. This review captures the development of silicon atom-based electronics and is divided into several sections that will cover characterization and atom manipulation of silicon surfaces with scanning tunneling microscopy and atomic force microscopy, development of silicon dangling bonds as atomic quantum dots, creation of atom scale devices, and the wiring and packaging of those circuits. The review will also cover the advance of silicon dangling bond logic design and the progress of silicon quantum atomic designer (SiQAD) simulators. Finally, an outlook of APM and silicon atom electronics will be provided.
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Affiliation(s)
- Jason Pitters
- Nanotechnology
Research Centre, National Research Council
of Canada, Edmonton, Alberta T6G 2M9, Canada
| | - Jeremiah Croshaw
- Department
of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
| | - Roshan Achal
- Department
of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
- Quantum
Silicon Inc., Edmonton, Alberta T6G 2M9, Canada
| | - Lucian Livadaru
- Department
of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
- Quantum
Silicon Inc., Edmonton, Alberta T6G 2M9, Canada
| | - Samuel Ng
- Department
of Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Robert Lupoiu
- School
of Engineering, Stanford University, Stanford, California 94305, United States
| | - Taras Chutora
- Department
of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
| | - Taleana Huff
- Canadian
Bank Note Company, Ottawa, Ontario K1Z 1A1, Canada
| | - Konrad Walus
- Department
of Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - Robert A. Wolkow
- Department
of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
- Quantum
Silicon Inc., Edmonton, Alberta T6G 2M9, Canada
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4
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Basso L, Kehayias P, Henshaw J, Saleh Ziabari M, Byeon H, Lilly MP, Bussmann E, Campbell DM, Misra S, Mounce AM. Electric current paths in a Si:P delta-doped device imaged by nitrogen-vacancy diamond magnetic microscopy. NANOTECHNOLOGY 2022; 34:015001. [PMID: 36170794 DOI: 10.1088/1361-6528/ac95a0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 09/28/2022] [Indexed: 06/16/2023]
Abstract
The recently-developed ability to control phosphorous-doping of silicon at an atomic level using scanning tunneling microscopy, a technique known as atomic precision advanced manufacturing (APAM), has allowed us to tailor electronic devices with atomic precision, and thus has emerged as a way to explore new possibilities in Si electronics. In these applications, critical questions include where current flow is actually occurring in or near APAM structures as well as whether leakage currents are present. In general, detection and mapping of current flow in APAM structures are valuable diagnostic tools to obtain reliable devices in digital-enhanced applications. In this paper, we used nitrogen-vacancy (NV) centers in diamond for wide-field magnetic imaging (with a few-mm field of view and micron-scale resolution) of magnetic fields from surface currents flowing in an APAM test device made of a P delta-doped layer on a Si substrate, a standard APAM witness material. We integrated a diamond having a surface NV ensemble with the device (patterned in two parallel mm-sized ribbons), then mapped the magnetic field from the DC current injected in the APAM device in a home-built NV wide-field microscope. The 2D magnetic field maps were used to reconstruct the surface current densities, allowing us to obtain information on current paths, device failures such as choke points where current flow is impeded, and current leakages outside the APAM-defined P-doped regions. Analysis on the current density reconstructed map showed a projected sensitivity of ∼0.03 A m-1, corresponding to a smallest-detectable current in the 200μm wide APAM ribbon of ∼6μA. These results demonstrate the failure analysis capability of NV wide-field magnetometry for APAM materials, opening the possibility to investigate other cutting-edge microelectronic devices.
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Affiliation(s)
- Luca Basso
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico NM-87123, United States of America
| | - Pauli Kehayias
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
| | - Jacob Henshaw
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico NM-87123, United States of America
| | - Maziar Saleh Ziabari
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico NM-87123, United States of America
- Center for High Technology Materials and Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico NM-87131, United States of America
| | - Heejun Byeon
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico NM-87123, United States of America
| | - Michael P Lilly
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico NM-87123, United States of America
| | - Ezra Bussmann
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico NM-87123, United States of America
| | - Deanna M Campbell
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
| | - Shashank Misra
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
| | - Andrew M Mounce
- Sandia National Laboratories, Albuquerque, New Mexico NM-87185, United States of America
- Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico NM-87123, United States of America
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5
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Islam S, Shamim S, Ghosh A. Benchmarking Noise and Dephasing in Emerging Electrical Materials for Quantum Technologies. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022:e2109671. [PMID: 35545231 DOI: 10.1002/adma.202109671] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Revised: 05/01/2022] [Indexed: 06/15/2023]
Abstract
As quantum technologies develop, a specific class of electrically conducting materials is rapidly gaining interest because they not only form the core quantum-enabled elements in superconducting qubits, semiconductor nanostructures, or sensing devices, but also the peripheral circuitry. The phase coherence of the electronic wave function in these emerging materials will be crucial when incorporated in the quantum architecture. The loss of phase memory, or dephasing, occurs when a quantum system interacts with the fluctuations in the local electromagnetic environment, which manifests in "noise" in the electrical conductivity. Hence, characterizing these materials and devices therefrom, for quantum applications, requires evaluation of both dephasing and noise, although there are very few materials where these properties are investigated simultaneously. Here, the available data on magnetotransport and low-frequency fluctuations in electrical conductivity are reviewed to benchmark the dephasing and noise. The focus is on new materials that are of direct interest to quantum technologies. The physical processes causing dephasing and noise in these systems are elaborated, the impact of both intrinsic and extrinsic parameters from materials synthesis and devices realization are evaluated, and it is hoped that a clearer pathway to design and characterize both material and devices for quantum applications is thus provided.
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Affiliation(s)
- Saurav Islam
- Department of Physics, Indian Institute of Science, Bengaluru, 560012, India
| | - Saquib Shamim
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Arindam Ghosh
- Department of Physics, Indian Institute of Science, Bengaluru, 560012, India
- Centre for Nano Science and Engineering, Indian Institute of Science, Bengaluru, 560012, India
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6
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Kölker A, Gramse G, Stock TJZ, Aeppli G, Curson NJ. In operando charge transport imaging of atomically thin dopant nanostructures in silicon. NANOSCALE 2022; 14:6437-6448. [PMID: 35416206 DOI: 10.1039/d1nr08381c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Novel approaches to materials design, fabrication processes and device architectures have accelerated next-generation electronics component production, pushing device dimensions down to the nano- and atomic-scale. For device metrology methods to keep up with these developments, they should not only measure the relevant electrical parameters at these length-scales, but ideally do so during active operation of the device. Here, we demonstrate such a capability using the full functionality of an advanced scanning microwave/scanning capacitance/kelvin probe atomic force microscope to inspect the charge transport and performance of an atomically thin buried phosphorus wire device during electrical operation. By interrogation of the contact potential, carrier density and transport properties, we demonstrate the capability to distinguish between the different material components and device imperfections, and assess their contributions to the overall electric characteristics of the device in operando. Our experimental methodology will facilitate rapid feedback for the fabrication of patterned nanoscale dopant device components in silicon, now important for the emerging field of silicon quantum information technology. More generally, the versatile setup, with its advanced inspection capabilities, delivers a comprehensive method to determine the performance of nanoscale devices while they function, in a broad range of material systems.
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Affiliation(s)
- Alexander Kölker
- London Centre of Nanotechnology, UCL, 17-19 Gordon Street, London WC1H 0AH, UK.
| | - Georg Gramse
- Johannes Kepler University, Biophysics Institute, Gruberstrasse 40, 4020 Linz, Austria
- Keysight Laboratories, Keysight Technologies, Inc., Gruberstrasse 40, 4020 Linz, Austria
| | - Taylor J Z Stock
- London Centre of Nanotechnology, UCL, 17-19 Gordon Street, London WC1H 0AH, UK.
| | - Gabriel Aeppli
- Department of Physics and Quantum Center, ETH, Zurich CH-8093, Switzerland
- Institut de Physique, EPFL, Lausanne CH-1015, Switzerland
- Paul Scherrer Institut, Villigen CH-5232, Switzerland
| | - Neil J Curson
- London Centre of Nanotechnology, UCL, 17-19 Gordon Street, London WC1H 0AH, UK.
- Department of Electronic and Electrical Engineering, UCL, Torrington Place, London, WC1E 7JE, UK
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7
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Ultra-shallow dopant profiles as in-situ electrodes in scanning probe microscopy. Sci Rep 2022; 12:3783. [PMID: 35260623 PMCID: PMC8904578 DOI: 10.1038/s41598-022-07551-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 02/21/2022] [Indexed: 11/25/2022] Open
Abstract
The application of nano materials to control advanced functionality in semiconductor devices has reached the atomic scale. At this dimension the exact chemical and structural composition of a device is crucial for its performance. Rapid inspection techniques are required to find the optimal combination among numerous materials. However, to date the earliest electrical inspection is carried out after multiple fabrication processes. This delay makes the fabrication of atomically designed components very challenging. Here, we propose a sample system to chemically characterize nanoscale devices in-operando. We introduce ion-implanted contacts which embedded in the sample serve as additional electrodes to carry out scanning gate experiments. We demonstrate that the presence of these electrodes does not deteriorate the surface quality. The potential of this approach is highlighted by controlling the charge state of single dangling bonds on the silicon surface. Apart from our novel sample holder, the experimental setup was not modified making this approach compatible to most commercial low-temperature scanning probe microscopes. For silicon based devices, the versatility of this method is a promising avenue to gain a detailed and rapid understanding of functionalized atomic devices and quantum interactions at the atomic level.
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8
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Electronic transport in planar atomic-scale structures measured by two-probe scanning tunneling spectroscopy. Nat Commun 2019; 10:1573. [PMID: 30952953 PMCID: PMC6450957 DOI: 10.1038/s41467-019-09315-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 02/27/2019] [Indexed: 11/09/2022] Open
Abstract
Miniaturization of electronic circuits into the single-atom level requires novel approaches to characterize transport properties. Due to its unrivaled precision, scanning probe microscopy is regarded as the method of choice for local characterization of atoms and single molecules supported on surfaces. Here we investigate electronic transport along the anisotropic germanium (001) surface with the use of two-probe scanning tunneling spectroscopy and first-principles transport calculations. We introduce a method for the determination of the transconductance in our two-probe experimental setup and demonstrate how it captures energy-resolved information about electronic transport through the unoccupied surface states. The sequential opening of two transport channels within the quasi-one-dimensional Ge dimer rows in the surface gives rise to two distinct resonances in the transconductance spectroscopic signal, consistent with phase-coherence lengths of up to 50 nm and anisotropic electron propagation. Our work paves the way for the electronic transport characterization of quantum circuits engineered on surfaces. Measuring electronic transport at the atomic scale requires atom precise contacts. Here, the authors demonstrate quasi-one-dimensional electronic transport along a single dimer row on a germanium surface using a two probe scanning tunneling microscopy protocol.
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9
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Škereň T, Pascher N, Garnier A, Reynaud P, Rolland E, Thuaire A, Widmer D, Jehl X, Fuhrer A. CMOS platform for atomic-scale device fabrication. NANOTECHNOLOGY 2018; 29:435302. [PMID: 30070975 DOI: 10.1088/1361-6528/aad7ab] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Controlled atomic scale fabrication based on scanning probe patterning or surface assembly typically involves a complex process flow, stringent requirements for an ultra-high vacuum environment, long fabrication times and, consequently, limited throughput and device yield. We demonstrate a device platform that overcomes these limitations by integrating scanning-probe based dopant device fabrication with a CMOS-compatible process flow. Silicon on insulator substrates are used featuring a reconstructed Si(001):H surface that is protected by a capping chip and has pre-implanted contacts ready for scanning tunneling microscope (STM) patterning. Processing in ultra-high vacuum is thereby reduced to a few critical steps. Subsequent reintegration of the samples into the CMOS process flow opens the door to successful application of STM fabricated dopant devices in more complex device architectures. Full functionality of this approach is demonstrated with magnetotransport measurements on degenerately doped STM patterned Si:P nanowires up to room temperature.
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Affiliation(s)
- Tomáš Škereň
- IBM Research-Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
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10
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Broome MA, Gorman SK, House MG, Hile SJ, Keizer JG, Keith D, Hill CD, Watson TF, Baker WJ, Hollenberg LCL, Simmons MY. Two-electron spin correlations in precision placed donors in silicon. Nat Commun 2018. [PMID: 29515115 PMCID: PMC5841377 DOI: 10.1038/s41467-018-02982-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Substitutional donor atoms in silicon are promising qubits for quantum computation with extremely long relaxation and dephasing times demonstrated. One of the critical challenges of scaling these systems is determining inter-donor distances to achieve controllable wavefunction overlap while at the same time performing high fidelity spin readout on each qubit. Here we achieve such a device by means of scanning tunnelling microscopy lithography. We measure anti-correlated spin states between two donor-based spin qubits in silicon separated by 16 ± 1 nm. By utilising an asymmetric system with two phosphorus donors at one qubit site and one on the other (2P−1P), we demonstrate that the exchange interaction can be turned on and off via electrical control of two in-plane phosphorus doped detuning gates. We determine the tunnel coupling between the 2P−1P system to be 200 MHz and provide a roadmap for the observation of two-electron coherent exchange oscillations. Donor impurities in silicon are promising candidates as qubits but in order to create a large-scale quantum computer inter-qubit coupling must be introduced by precise positioning of the donors. Here the authors demonstrate the fabrication, manipulation and readout of a two qubit phosphorous donor device.
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Affiliation(s)
- M A Broome
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - S K Gorman
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - M G House
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - S J Hile
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - J G Keizer
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - D Keith
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - C D Hill
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - T F Watson
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - W J Baker
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia
| | - L C L Hollenberg
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, The University of Melbourne, Parkville, VIC, 3010, Australia
| | - M Y Simmons
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW, 2052, Australia.
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11
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Wang X, Hagmann JA, Namboodiri P, Wyrick J, Li K, Murray RE, Myers A, Misenkosen F, Stewart MD, Richter CA, Silver RM. Quantifying atom-scale dopant movement and electrical activation in Si:P monolayers. NANOSCALE 2018; 10:4488-4499. [PMID: 29459919 PMCID: PMC11305481 DOI: 10.1039/c7nr07777g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Advanced hydrogen lithography techniques and low-temperature epitaxial overgrowth enable the patterning of highly phosphorus-doped silicon (Si:P) monolayers (ML) with atomic precision. This approach to device fabrication has made Si:P monolayer systems a testbed for multiqubit quantum computing architectures and atomically precise 2-D superlattice designs whose behaviors are directly tied to the deterministic placement of single dopants. However, dopant segregation, diffusion, surface roughening, and defect formation during the encapsulation overgrowth introduce large uncertainties to the exact dopant placement and activation ratio. In this study, we develop a unique method by combining dopant segregation/diffusion models with sputter profiling simulation to monitor and control, at the atomic scale, dopant movement using room-temperature grown locking layers (LLs). We explore the impact of LL growth rate, thickness, rapid thermal annealing, surface accumulation, and growth front roughness on dopant confinement, local crystalline quality, and electrical activation within Si:P 2-D systems. We demonstrate that dopant movement can be more efficiently suppressed by increasing the LL growth rate than by increasing the LL thickness. We find that the dopant segregation length can be suppressed below a single Si lattice constant by increasing the LL growth rates at room temperature while maintaining epitaxy. Although dopant diffusivity within the LL is found to remain high (on the order of 10-17 cm2 s-1) even below the hydrogen desorption temperature, we demonstrate that exceptionally sharp dopant confinement with high electrical quality within Si:P monolayers can be achieved by combining a high LL growth rate with low-temperature LL rapid thermal annealing. The method developed in this study provides a key tool for 2-D fabrication techniques that require precise dopant placement to suppress, quantify, and predict a single dopant's movement at the atomic scale.
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Affiliation(s)
- Xiqiao Wang
- National Institute of Standards and Technology, 100 Bureau Dr., Gaithersburg, Maryland 20899, USA.
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12
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Broome MA, Watson TF, Keith D, Gorman SK, House MG, Keizer JG, Hile SJ, Baker W, Simmons MY. High-Fidelity Single-Shot Singlet-Triplet Readout of Precision-Placed Donors in Silicon. PHYSICAL REVIEW LETTERS 2017; 119:046802. [PMID: 29341777 DOI: 10.1103/physrevlett.119.046802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Indexed: 06/07/2023]
Abstract
In this work we perform direct single-shot readout of the singlet-triplet states in exchange coupled electrons confined to precision-placed donor atoms in silicon. Our method takes advantage of the large energy splitting given by the Pauli-spin blockaded (2,0) triplet states, from which we can achieve a single-shot readout fidelity of 98.4±0.2%. We measure the triplet-minus relaxation time to be of the order 3 s at 2.5 T and observe its predicted decrease as a function of magnetic field, reaching 0.5 s at 1 T.
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Affiliation(s)
- M A Broome
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - T F Watson
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - D Keith
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - S K Gorman
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - M G House
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - J G Keizer
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - S J Hile
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - W Baker
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - M Y Simmons
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
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13
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Deng X, Namboodiri P, Li K, Wang X, Stan G, Myers AF, Cheng X, Li T, Silver RM. Silicon epitaxy on H-terminated Si (100) surfaces at 250 °C. APPLIED SURFACE SCIENCE 2016; 378:301-307. [PMID: 27397949 PMCID: PMC4929620 DOI: 10.1016/j.apsusc.2016.03.212] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Low temperature Si epitaxy has become increasingly important due to its critical role in the encapsulation and performance of buried nanoscale dopant devices. We demonstrate epitaxial growth up to nominally 25 nm, at 250°C, with analysis at successive growth steps using STM and cross section TEM to reveal the nature and quality of the epitaxial growth. STM images indicate that growth morphology of both Si on Si and Si on H-terminated Si (H: Si) is epitaxial in nature at temperatures as low as 250 °C. For Si on Si growth at 250 °C, we show that the Si epitaxial growth front maintains a constant morphology after reaching a specific thickness threshold. Although the in-plane mobility of silicon is affected on the H: Si surface due to the presence of H atoms during initial sub-monolayer growth, STM images reveal long range order and demonstrate that growth proceeds by epitaxial island growth albeit with noticeable surface roughening.
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Affiliation(s)
- Xiao Deng
- School of Physics Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China; National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Pradeep Namboodiri
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Kai Li
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Xiqiao Wang
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States; University of Maryland, College Park, Maryland 20740, United States
| | - Gheorghe Stan
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Alline F Myers
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Xinbin Cheng
- School of Physics Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China
| | - Tongbao Li
- School of Physics Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China
| | - Richard M Silver
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
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14
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Engelund M, Godlewski S, Kolmer M, Zuzak R, Such B, Frederiksen T, Szymonski M, Sánchez-Portal D. The butterfly - a well-defined constant-current topography pattern on Si(001):H and Ge(001):H resulting from current-induced defect fluctuations. Phys Chem Chem Phys 2016; 18:19309-17. [PMID: 27375264 DOI: 10.1039/c6cp04031d] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Dangling bond (DB) arrays on Si(001):H and Ge(001):H surfaces can be patterned with atomic precision and they exhibit complex and rich physics making them interesting from both technological and fundamental perspectives. But their complex behavior often makes scanning tunneling microscopy (STM) images difficult to interpret and simulate. Recently it was shown that low-temperature imaging of unoccupied states of an unpassivated dimer on Ge(001):H results in a symmetric butterfly-like STM pattern, despite the fact that the equilibrium dimer configuration is expected to be a bistable, buckled geometry. Here, based on a thorough characterization of the low-bias switching events on Ge(001):H, we propose a new imaging model featuring a dynamical two-state rate equation. On both Si(001):H and Ge(001):H, this model allows us to reproduce the features of the observed symmetric empty-state images which strongly corroborates the idea that the patterns arise due to fast switching events and provides an insight into the relationship between the tunneling current and switching rates. We envision that our new imaging model can be applied to simulate other bistable systems where fluctuations arise from transiently charged electronic states.
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Affiliation(s)
- Mads Engelund
- Centro de Física de Materiales (CFM), CSIC-UPV/EHU, Paseo Manuel de Lardizabal 5, 20018, Donostia-San Sebastián, Spain.
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15
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Watson TF, Weber B, House MG, Büch H, Simmons MY. High-Fidelity Rapid Initialization and Read-Out of an Electron Spin via the Single Donor D(-) Charge State. PHYSICAL REVIEW LETTERS 2015; 115:166806. [PMID: 26550896 DOI: 10.1103/physrevlett.115.166806] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2015] [Indexed: 05/14/2023]
Abstract
We demonstrate high-fidelity electron spin read-out of a precision placed single donor in silicon via spin selective tunneling to either the D(+) or D(-) charge state of the donor. By performing read-out at the stable two electron D(0)↔D(-) charge transition we can increase the tunnel rates to a nearby single electron transistor charge sensor by nearly 2 orders of magnitude, allowing faster qubit read-out (1 ms) with minimum loss in read-out fidelity (98.4%) compared to read-out at the D(+)↔D(0) transition (99.6%). Furthermore, we show that read-out via the D(-) charge state can be used to rapidly initialize the electron spin qubit in its ground state with a fidelity of F(I)=99.8%.
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Affiliation(s)
- T F Watson
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - B Weber
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - M G House
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - H Büch
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - M Y Simmons
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales, Sydney, New South Wales 2052, Australia
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16
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Engelund M, Zuzak R, Godlewski S, Kolmer M, Frederiksen T, García-Lekue A, Sánchez-Portal D, Szymonski M. Tunneling spectroscopy of close-spaced dangling-bond pairs in Si(001):H. Sci Rep 2015; 5:14496. [PMID: 26404520 PMCID: PMC4585918 DOI: 10.1038/srep14496] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 09/01/2015] [Indexed: 11/12/2022] Open
Abstract
We present a combined experimental and theoretical study of the electronic properties of close-spaced dangling-bond (DB) pairs in a hydrogen-passivated Si(001):H p-doped surface. Two types of DB pairs are considered, called “cross” and “line” structures. Our scanning tunneling spectroscopy (STS) data show that, although the spectra taken over different DBs in each pair exhibit a remarkable resemblance, they appear shifted by a constant energy that depends on the DB-pair type. This spontaneous asymmetry persists after repeated STS measurements. By comparison with density functional theory (DFT) calculations, we demonstrate that the magnitude of this shift and the relative position of the STS peaks can be explained by distinct charge states for each DB in the pair. We also explain how the charge state is modified by the presence of the scanning tunneling microscopy (STM) tip and the applied bias. Our results indicate that, using the STM tip, it is possible to control the charge state of individual DBs in complex structures, even if they are in close proximity. This observation might have important consequences for the design of electronic circuits and logic gates based on DBs in passivated silicon surfaces.
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Affiliation(s)
- Mads Engelund
- Centro de Física de Materiales CSIC-UPV/EHU, Paseo Manual de Lardizabal 5, E-20018, Donostia-San Sebastián, Spain
| | - Rafał Zuzak
- Center for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, PL-30-348, Krakow, Poland
| | - Szymon Godlewski
- Center for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, PL-30-348, Krakow, Poland
| | - Marek Kolmer
- Center for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, PL-30-348, Krakow, Poland
| | - Thomas Frederiksen
- Donostia International Physics Center, Paseo Manual de Lardizabal 4, 20018, Donostia-San Sebastián, Spain.,IKERBASQUE, Basque Foundation for Science, E-48013, Bilbao, Spain
| | - Aran García-Lekue
- Donostia International Physics Center, Paseo Manual de Lardizabal 4, 20018, Donostia-San Sebastián, Spain.,IKERBASQUE, Basque Foundation for Science, E-48013, Bilbao, Spain
| | - Daniel Sánchez-Portal
- Centro de Física de Materiales CSIC-UPV/EHU, Paseo Manual de Lardizabal 5, E-20018, Donostia-San Sebastián, Spain.,Donostia International Physics Center, Paseo Manual de Lardizabal 4, 20018, Donostia-San Sebastián, Spain
| | - Marek Szymonski
- Center for Nanometer-Scale Science and Advanced Materials, NANOSAM, Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, PL-30-348, Krakow, Poland
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17
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Lo CC, Urdampilleta M, Ross P, Gonzalez-Zalba MF, Mansir J, Lyon SA, Thewalt MLW, Morton JJL. Hybrid optical-electrical detection of donor electron spins with bound excitons in silicon. NATURE MATERIALS 2015; 14:490-494. [PMID: 25799326 DOI: 10.1038/nmat4250] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 02/12/2015] [Indexed: 06/04/2023]
Abstract
Electrical detection of spins is an essential tool for understanding the dynamics of spins, with applications ranging from optoelectronics and spintronics, to quantum information processing. For electron spins bound to donors in silicon, bulk electrically detected magnetic resonance has relied on coupling to spin readout partners such as paramagnetic defects or conduction electrons, which fundamentally limits spin coherence times. Here we demonstrate electrical detection of donor electron spin resonance in an ensemble by transport through a silicon device, using optically driven donor-bound exciton transitions. We measure electron spin Rabi oscillations, and obtain long electron spin coherence times, limited only by the donor concentration. We also experimentally address critical issues such as non-resonant excitation, strain, and electric fields, laying the foundations for realizing a single-spin readout method with relaxed magnetic field and temperature requirements compared with spin-dependent tunnelling, enabling donor-based technologies such as quantum sensing.
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Affiliation(s)
- C C Lo
- 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, UK
| | - M Urdampilleta
- London Centre for Nanotechnology, University College London, London WC1H 0AH, UK
| | - P Ross
- London Centre for Nanotechnology, University College London, London WC1H 0AH, UK
| | - M F Gonzalez-Zalba
- Hitachi Cambridge Laboratory, J. J. Thomson Avenue Cambridge CB3 0HE, UK
| | - J Mansir
- London Centre for Nanotechnology, University College London, London WC1H 0AH, UK
| | - S A Lyon
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - M L W Thewalt
- Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
| | - J J L Morton
- 1] London Centre for Nanotechnology, University College London, London WC1H 0AH, UK [2] Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, UK
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18
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Ryu H, Lee S, Fuechsle M, Miwa JA, Mahapatra S, Hollenberg LCL, Simmons MY, Klimeck G. A tight-binding study of single-atom transistors. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2015; 11:374-381. [PMID: 25293353 DOI: 10.1002/smll.201400724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Revised: 07/29/2014] [Indexed: 06/03/2023]
Abstract
A detailed theoretical study of the electronic and transport properties of a single atom transistor, where a single phosphorus atom is embedded within a single crystal transistor architecture, is presented. Using a recently reported deterministic single-atom transistor as a reference, the electronic structure of the device is represented atomistically with a tight-binding model, and the channel modulation is simulated self-consistently with a Thomas-Fermi method. The multi-scale modeling approach used allows confirmation of the charging energy of the one-electron donor charge state and explains how the electrostatic environments of the device electrodes affects the donor confinement potential and hence extent in gate voltage of the two-electron charge state. Importantly, whilst devices are relatively insensitive to dopant ordering in the highly doped leads, a ∼1% variation of the charging energy is observed when a dopant is moved just one lattice spacing within the device. The multi-scale modeling method presented here lays a strong foundation for the understanding of single-atom device structures: essential for both classical and quantum information processing.
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Affiliation(s)
- Hoon Ryu
- National Institute of Supercomputing and Networking, Korea Institute of Science and Technology Information, Daejeon, 305-806, Republic of Korea; Network for Computational Nanotechnology, Purdue University, Indiana, 47907, USA
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19
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Weber B, Ryu H, Tan YHM, Klimeck G, Simmons MY. Limits to metallic conduction in atomic-scale quasi-one-dimensional silicon wires. PHYSICAL REVIEW LETTERS 2014; 113:246802. [PMID: 25541793 DOI: 10.1103/physrevlett.113.246802] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Indexed: 06/04/2023]
Abstract
The recent observation of ultralow resistivity in highly doped, atomic-scale silicon wires has sparked interest in what limits conduction in these quasi-1D systems. Here we present electron transport measurements of gated Si:P wires of widths 4.6 and 1.5 nm. At 4.6 nm we find an electron mobility, μ(el)≃60 cm²/V s, in excellent agreement with that of macroscopic Hall bars. Metallic conduction persists to millikelvin temperatures where we observe Gaussian conductance fluctuations of order δG∼e²/h. In thinner wires (1.5 nm), metallic conduction breaks down at G≲e²/h, where localization of carriers leads to Coulomb blockade. Metallic behavior is explained by the large carrier densities in Si:P δ-doped systems, allowing the occupation of all six valleys of the silicon conduction band, enhancing the number of 1D channels and hence the localization length.
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Affiliation(s)
- Bent Weber
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Hoon Ryu
- National Institute of Supercomputing and Networking, KISTI, Daejeon 305-806, South Korea
| | - Y-H Matthias Tan
- Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - Gerhard Klimeck
- Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - Michelle Y Simmons
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
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20
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Lee WCT, McKibbin SR, Thompson DL, Xue K, Scappucci G, Bishop N, Celler GK, Carroll MS, Simmons MY. Lithography and doping in strained Si towards atomically precise device fabrication. NANOTECHNOLOGY 2014; 25:145302. [PMID: 24633016 DOI: 10.1088/0957-4484/25/14/145302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We investigate the ability to introduce strain into atomic-scale silicon device fabrication by performing hydrogen lithography and creating electrically active phosphorus δ-doped silicon on strained silicon-on-insulator (sSOI) substrates. Lithographic patterns were obtained by selectively desorbing hydrogen atoms from a H resist layer adsorbed on a clean, atomically flat sSOI(001) surface with a scanning tunnelling microscope tip operating in ultra-high vacuum. The influence of the tip-to-sample bias on the lithographic process was investigated allowing us to pattern feature-sizes from several microns down to 1.3 nm. In parallel we have investigated the impact of strain on the electrical properties of P:Si δ-doped layers. Despite the presence of strain inducing surface variations in the silicon substrate we still achieve high carrier densities (>1.0 × 10(14) cm(-2)) with mobilities of ∼100 cm(2) V(-1) s(-1). These results open up the possibility of a scanning-probe lithography approach to the fabrication of strained atomic-scale devices in silicon.
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Affiliation(s)
- W C T Lee
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
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21
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Watson TF, Weber B, Miwa JA, Mahapatra S, Heijnen RMP, Simmons MY. Transport in asymmetrically coupled donor-based silicon triple quantum dots. NANO LETTERS 2014; 14:1830-1835. [PMID: 24661142 DOI: 10.1021/nl4045026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We demonstrate serial electron transport through a donor-based triple quantum dot in silicon fabricated with nanoscale precision by scanning tunnelling microscopy lithography. From an equivalent circuit model, we calculate the electrochemical potentials of the dots allowing us to identify ground and excited states in finite bias transport. Significantly, we show that using a scanning tunnelling microscope, we can directly demonstrate that a ∼1 nm difference in interdot distance dramatically affects transport pathways between the three dots.
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Affiliation(s)
- Thomas F Watson
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales , Sydney, New South Wales 2052, Australia
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22
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Ryu H, Lee S, Weber B, Mahapatra S, Hollenberg LCL, Simmons MY, Klimeck G. Atomistic modeling of metallic nanowires in silicon. NANOSCALE 2013; 5:8666-8674. [PMID: 23897026 DOI: 10.1039/c3nr01796f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Scanning tunneling microscope (STM) lithography has recently demonstrated the ultimate in device scaling with buried, conducting nanowires just a few atoms wide and the realization of single atom transistors, where a single P atom has been placed inside a transistor architecture with atomic precision accuracy. Despite the dimensions of the critical parts of these devices being defined by a small number of P atoms, the device electronic properties are influenced by the surrounding 10(4) to 10(6) Si atoms. Such effects are hard to capture with most modeling approaches, and prior to this work no theory existed that could explore the realistic size of the complete device in which both dopant disorder and placement are important. This work presents a comprehensive study of the electronic and transport properties of ultra-thin (<10 nm wide) monolayer highly P δ-doped Si (Si:P) nanowires in a fully atomistic self-consistent tight-binding approach. This atomistic approach covering large device volumes allows for a systematic study of disorder on the physical properties of the nanowires. Excellent quantitative agreement is observed with recent resistance measurements of STM-patterned nanowires [Weber et al., Science, 2012, 335, 64], confirming the presence of metallic behavior at the scaling limit. At high doping densities the channel resistance is shown to be insensitive to the exact channel dopant placement highlighting their future use as metallic interconnects. This work presents the first theoretical study of Si:P nanowires that are realistically extended and disordered, providing a strong theoretical foundation for the design and understanding of atomic-scale electronics.
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Affiliation(s)
- Hoon Ryu
- National Institute of Supercomputing and Networking, Korea Institute of Science and Technology Information, Daejeon 305-806, Republic of Korea
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23
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Scappucci G, Capellini G, Klesse WM, Simmons MY. New avenues to an old material: controlled nanoscale doping of germanium. NANOSCALE 2013; 5:2600-2615. [PMID: 23455600 DOI: 10.1039/c3nr34258a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We review our recent research into n-type doping of Ge for nanoelectronics and integrated photonics. We demonstrate a doping method in ultra-high vacuum to achieve high electron concentrations in Ge while maintaining atomic-level control of the doping process. We integrated this doping technique with ultra-high vacuum scanning tunneling microscope lithography and femtosecond laser ablation micron-scale lithography, and demonstrated basic components of donor-based nanoelectronic circuitry such as wires and tunnel gaps. By repetition of controlled doping cycles we have shown that stacking of multiple Ge:P two-dimensional electron gases results in high electron densities in Ge (>10(20) cm(-3)). Because of the strong vertical electron confinement, closely stacked 2D layers - although interacting - maintain their individuality in terms of electron transport. These results bode well towards the realization of nanoscale 3D epitaxial circuits in Ge comprising stacked 2DEGs and/or atomic-scale Ge:P devices with confinement in more dimensions.
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Affiliation(s)
- Giordano Scappucci
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
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24
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Kepenekian M, Robles R, Joachim C, Lorente N. Surface-state engineering for interconnects on H-passivated Si(100). NANO LETTERS 2013; 13:1192-1195. [PMID: 23432608 DOI: 10.1021/nl304611m] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Surface-state engineering strategies for atomic-size interconnects on H-passivated Si(100) surfaces are explored. The well-known simple interconnect formed by removing H-atoms from one of the Si atoms per dimer of a dimer row along the Si(100) surface is poorly conducting. This is because one-dimensional-like instabilities open electronic gaps. Here, we explore two strategies to reduce the instabilities: spacing the dangling bonds with H atoms and changing the geometry by increasing the lateral size of the wires. The resulting wires are evaluated using density functional theory. Surprisingly, zigzag dangling-bond wires attain atomically confined conduction properties comparable with the conduction of free-standing metallic monatomic wires. These results hint at band-engineering strategies for the development of electronically driven nanocircuits.
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Affiliation(s)
- Mikaël Kepenekian
- Centro de Investigación en Nanociencia y Nanotecnología CIN2 (CSIC-ICN), Campus de la UAB, E-08193 Bellaterra, Spain.
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25
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Drumm DW, Budi A, Per MC, Russo SP, L Hollenberg LC. Ab initio calculation of valley splitting in monolayer δ-doped phosphorus in silicon. NANOSCALE RESEARCH LETTERS 2013; 8:111. [PMID: 23445785 PMCID: PMC3606473 DOI: 10.1186/1556-276x-8-111] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Accepted: 01/26/2013] [Indexed: 05/29/2023]
Abstract
: The differences in energy between electronic bands due to valley splitting are of paramount importance in interpreting transport spectroscopy experiments on state-of-the-art quantum devices defined by scanning tunnelling microscope lithography. Using vasp, we develop a plane-wave density functional theory description of systems which is size limited due to computational tractability. Nonetheless, we provide valuable data for the benchmarking of empirical modelling techniques more capable of extending this discussion to confined disordered systems or actual devices. We then develop a less resource-intensive alternative via localised basis functions in siesta, retaining the physics of the plane-wave description, and extend this model beyond the capability of plane-wave methods to determine the ab initio valley splitting of well-isolated δ-layers. In obtaining an agreement between plane-wave and localised methods, we show that valley splitting has been overestimated in previous ab initio calculations by more than 50%.
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Affiliation(s)
- Daniel W Drumm
- School of Physics, The University of Melbourne, Parkville, Victoria 3010, Australia
- School of Applied Sciences, RMIT University, Melbourne, Victoria 3001, Australia
| | - Akin Budi
- School of Physics, The University of Melbourne, Parkville, Victoria 3010, Australia
- School of Applied Sciences, RMIT University, Melbourne, Victoria 3001, Australia
| | - Manolo C Per
- School of Applied Sciences, RMIT University, Melbourne, Victoria 3001, Australia
- Virtual Nanoscience Laboratory, CSIRO Materials Science and Engineering, Parkville, Victoria 3052, Australia
| | - Salvy P Russo
- School of Applied Sciences, RMIT University, Melbourne, Victoria 3001, Australia
| | - Lloyd C L Hollenberg
- School of Physics, The University of Melbourne, Parkville, Victoria 3010, Australia
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26
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McKibbin SR, Scappucci G, Pok W, Simmons MY. Epitaxial top-gated atomic-scale silicon wire in a three-dimensional architecture. NANOTECHNOLOGY 2013; 24:045303. [PMID: 23291418 DOI: 10.1088/0957-4484/24/4/045303] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Three-dimensional (3D) control of dopant profiles in silicon is a critical requirement for fabricating atomically precise transistors. We demonstrate conductance modulation through an atomic scale 3 nm wide δ-doped silicon-phosphorus wire using a vertically separated epitaxial doped Si:P top-gate. We show that intrinsic crystalline silicon grown at low temperatures (∼250 °C) serves as an effective gate dielectric permitting us to achieve large gate ranges (∼2.6 V) with leakage currents below 1 pA. Combining scanning tunneling lithography for precise lateral confinement, with monolayer doping and low temperature epitaxial overgrowth for precise vertical confinement, we can realize multiple layers of nano-patterned dopants in a single crystal material. These results demonstrate the viability of highly doped, vertically separated epitaxial gates in an all-crystalline architecture with long-term implications for monolithic 3D silicon circuits and for the realization of atomically precise donor architectures for quantum computing.
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Affiliation(s)
- S R McKibbin
- Centre of Excellence for Quantum Computation and Communication Technology and School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
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27
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Weber B, Mahapatra S, Watson TF, Simmons MY. Engineering independent electrostatic control of atomic-scale (∼4 nm) silicon double quantum dots. NANO LETTERS 2012; 12:4001-4006. [PMID: 22686257 DOI: 10.1021/nl3012903] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Scalable quantum computing architectures with electronic spin qubits hosted by arrays of single phosphorus donors in silicon require local electric and magnetic field control of individual qubits separated by ∼10 nm. This daunting task not only requires atomic-scale accuracy of single P donor positioning to control interqubit exchange interaction but also demands precision alignment of control electrodes with careful device design at these small length scales to minimize cross capacitive coupling. Here we demonstrate independent electrostatic control of two Si:P quantum dots, each consisting of ∼15 P donors, in an optimized device design fabricated by scanning tunneling microscope (STM)-based lithography. Despite the atomic-scale dimensions of the quantum dots and control electrodes reducing overall capacitive coupling, the electrostatic behavior of the device shows an excellent match to results of a priori capacitance calculations. These calculations highlight the importance of the interdot angle in achieving independent control at these length-scales. This combination of predictive electrostatic modeling and the atomic-scale fabrication accuracy of STM-lithography, provides a powerful tool for scaling multidonor dots to the single donor limit.
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Affiliation(s)
- Bent Weber
- Centre for Quantum Computation and Communication Technology, School of Physics, The University of New South Wales, Sydney, NSW 2052, Australia
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28
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Culcer D, Saraiva AL, Koiller B, Hu X, Das Sarma S. Valley-based noise-resistant quantum computation using Si quantum dots. PHYSICAL REVIEW LETTERS 2012; 108:126804. [PMID: 22540611 DOI: 10.1103/physrevlett.108.126804] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Indexed: 05/31/2023]
Abstract
We devise a platform for noise-resistant quantum computing using the valley degree of freedom of Si quantum dots. The qubit is encoded in two polarized (1,1) spin-triplet states with different valley compositions in a double quantum dot, with a Zeeman field enabling unambiguous initialization. A top gate gives a difference in the valley splitting between the dots, allowing controllable interdot tunneling between opposite valley eigenstates, which enables one-qubit rotations. Two-qubit operations rely on a stripline resonator, and readout on charge sensing. Sensitivity to charge and spin fluctuations is determined by intervalley processes and is greatly reduced as compared to conventional spin and charge qubits. We describe a valley echo for further noise suppression.
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Affiliation(s)
- Dimitrie Culcer
- ICQD, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
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Fuechsle M, Miwa JA, Mahapatra S, Ryu H, Lee S, Warschkow O, Hollenberg LCL, Klimeck G, Simmons MY. A single-atom transistor. NATURE NANOTECHNOLOGY 2012; 7:242-6. [PMID: 22343383 DOI: 10.1038/nnano.2012.21] [Citation(s) in RCA: 283] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 01/26/2012] [Indexed: 05/03/2023]
Abstract
The ability to control matter at the atomic scale and build devices with atomic precision is central to nanotechnology. The scanning tunnelling microscope can manipulate individual atoms and molecules on surfaces, but the manipulation of silicon to make atomic-scale logic circuits has been hampered by the covalent nature of its bonds. Resist-based strategies have allowed the formation of atomic-scale structures on silicon surfaces, but the fabrication of working devices-such as transistors with extremely short gate lengths, spin-based quantum computers and solitary dopant optoelectronic devices-requires the ability to position individual atoms in a silicon crystal with atomic precision. Here, we use a combination of scanning tunnelling microscopy and hydrogen-resist lithography to demonstrate a single-atom transistor in which an individual phosphorus dopant atom has been deterministically placed within an epitaxial silicon device architecture with a spatial accuracy of one lattice site. The transistor operates at liquid helium temperatures, and millikelvin electron transport measurements confirm the presence of discrete quantum levels in the energy spectrum of the phosphorus atom. We find a charging energy that is close to the bulk value, previously only observed by optical spectroscopy.
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Affiliation(s)
- Martin Fuechsle
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
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Weber B, Mahapatra S, Ryu H, Lee S, Fuhrer A, Reusch TCG, Thompson DL, Lee WCT, Klimeck G, Hollenberg LCL, Simmons MY. Ohm’s Law Survives to the Atomic Scale. Science 2012; 335:64-7. [DOI: 10.1126/science.1214319] [Citation(s) in RCA: 263] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- B. Weber
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - S. Mahapatra
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - H. Ryu
- Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA
| | - S. Lee
- Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA
| | - A. Fuhrer
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - T. C. G. Reusch
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - D. L. Thompson
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - W. C. T. Lee
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - G. Klimeck
- Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA
| | - L. C. L. Hollenberg
- Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville, VIC 3010, Australia
| | - M. Y. Simmons
- Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
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Mahapatra S, Büch H, Simmons MY. Charge sensing of precisely positioned p donors in Si. NANO LETTERS 2011; 11:4376-81. [PMID: 21919458 DOI: 10.1021/nl2025079] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Real-time sensing of (spin-dependent) single-electron tunneling is fundamental to electrical readout of qubit states in spin quantum computing. Here, we demonstrate the feasibility of detecting such single-electron tunneling events using an atomically planar charge sensing layout, which can be readily integrated in scalable quantum computing architectures with phosphorus-donor-based spin qubits in silicon (Si:P). Using scanning tunneling microscopy (STM) lithography on a Si(001) surface, we patterned a single-electron transistor (SET), both tunnel and electrostatically coupled to a coplanar ultrasmall quantum dot, the latter consisting of approximately four P donors. Charge transitions of the quantum dot could be detected both in time-averaged and single-shot current response of the SET. Single electron tunneling between the quantum dot and the SET island on a time-scale (τ ∼ ms) two-orders-of-magnitude faster than the spin-lattice relaxation time of a P donor in Si makes this device geometry suitable for projective readout of Si:P spin qubits. Crucial to scalability is the ability to reproducibly achieve sufficient electron tunnel rates and charge sensitivity of the SET. The inherent atomic-scale control of STM lithography bodes extremely well to precisely optimize both of these parameters.
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Affiliation(s)
- Suddhasatta Mahapatra
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, University of New South Wales, Sydney, NSW 2052, Australia
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Abstract
Scaling down the size of computing circuits is about to reach the limitations imposed by the discrete atomic structure of matter. Reducing the power requirements and thereby dissipation of integrated circuits is also essential. New paradigms are needed to sustain the rate of progress that society has become used to. Single-atom transistors, SATs, cascaded in a circuit are proposed as a promising route that is compatible with existing technology. We demonstrate the use of quantum degrees of freedom to perform logic operations in a complementary-metal-oxide-semiconductor device. Each SAT performs multilevel logic by electrically addressing the electronic states of a dopant atom. A single electron transistor decodes the physical multivalued output into the conventional binary output. A robust scalable circuit of two concatenated full adders is reported, where by utilizing charge and quantum degrees of freedom, the functionality of the transistor is pushed far beyond that of a simple switch.
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Scappucci G, Capellini G, Johnston B, Klesse WM, Miwa JA, Simmons MY. A complete fabrication route for atomic-scale, donor-based devices in single-crystal germanium. NANO LETTERS 2011; 11:2272-2279. [PMID: 21553900 DOI: 10.1021/nl200449v] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Despite the rapidly growing interest in Ge for ultrascaled classical transistors and innovative quantum devices, the field of Ge nanoelectronics is still in its infancy. One major hurdle has been electron confinement since fast dopant diffusion occurs when traditional Si CMOS fabrication processes are applied to Ge. We demonstrate a complete fabrication route for atomic-scale, donor-based devices in single-crystal Ge using a combination of scanning tunneling microscope lithography and high-quality crystal growth. The cornerstone of this fabrication process is an innovative lithographic procedure based on direct laser patterning of the semiconductor surface, allowing the gap between atomic-scale STM-patterned structures and the outside world to be bridged. Using this fabrication process, we show electron confinement in a 5 nm wide phosphorus-doped nanowire in single-crystal Ge. At cryogenic temperatures, Ohmic behavior is observed and a low planar resistivity of 8.3 kΩ/□ is measured.
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Affiliation(s)
- G Scappucci
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
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Klesse WM, Scappucci G, Capellini G, Simmons MY. Preparation of the Ge(001) surface towards fabrication of atomic-scale germanium devices. NANOTECHNOLOGY 2011; 22:145604. [PMID: 21368353 DOI: 10.1088/0957-4484/22/14/145604] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We demonstrate the preparation of a clean Ge(001) surface with minimal roughness (RMS ~0.6 Å), low defect densities (~0.2% ML) and wide mono-atomic terraces (~80-100 nm). We use an ex situ wet chemical process combined with an in situ anneal treatment followed by a homoepitaxial buffer layer grown by molecular beam epitaxy and a subsequent final thermal anneal. Using scanning tunneling microscopy, we investigate the effect on the surface morphology of using different chemical reagents, concentrations as well as substrate temperature during growth. Such a high quality Ge(001) surface enables the formation of defect-free H-terminated Ge surfaces for subsequent patterning of atomic-scale devices by scanning tunneling lithography. We have achieved atomic-scale dangling bond wire structures 1.6 nm wide and 40 nm long as well as large, micron-size patterns with clear contrast of lithography in STM images.
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Affiliation(s)
- W M Klesse
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
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Carter DJ, Marks NA, Warschkow O, McKenzie DR. Phosphorus δ-doped silicon: mixed-atom pseudopotentials and dopant disorder effects. NANOTECHNOLOGY 2011; 22:065701. [PMID: 21212477 DOI: 10.1088/0957-4484/22/6/065701] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Within a full density functional theory framework we calculate the band structure and doping potential for phosphorus δ-doped silicon. We compare two different representations of the dopant plane; pseudo-atoms in which the nuclear charge is fractional between silicon and phosphorus, and explicit arrangements employing distinct silicon and phosphorus atoms. While the pseudo-atom approach offers several computational advantages, the explicit model calculations differ in a number of key points, including the valley splitting, the Fermi level and the width of the doping potential. These findings have implications for parameters used in device modelling.
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Affiliation(s)
- Damien J Carter
- Nanochemistry Research Institute, Curtin University, Perth, WA, Australia.
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Lin H, Rauba JMC, Thygesen KS, Jacobsen KW, Simmons MY, Hofer WA. First-principles modelling of scanning tunneling microscopy using non-equilibrium Green’s functions. ACTA ACUST UNITED AC 2010. [DOI: 10.1007/s11467-010-0133-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Escott CC, Zwanenburg FA, Morello A. Resonant tunnelling features in quantum dots. NANOTECHNOLOGY 2010; 21:274018. [PMID: 20571205 DOI: 10.1088/0957-4484/21/27/274018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We present a systematic review of features due to resonant electron tunnelling, observable in transport spectroscopy experiments on quantum dots and single donors. The review covers features attributable to intrinsic properties of the dot (orbital, spin and valley states) as well as extrinsic effects (phonon/photon emission/absorption, features in the charge reservoirs, coupling to nearby charge centres). We focus on the most common operating conditions, neglecting effects due to strong coupling to the leads. By discussing the experimental signatures of each type of feature, we aim at providing practical methods to distinguish between their different physical origins. The correct classification of the resonant tunnelling features is an essential requirement to understand the details of the confining potential or to predict the performance of the dot for quantum information processing.
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Affiliation(s)
- C C Escott
- Australian Research Council Centre of Excellence for Quantum Computer Technology, School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, NSW 2052, Australia
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Fuechsle M, Mahapatra S, Zwanenburg FA, Friesen M, Eriksson MA, Simmons MY. Spectroscopy of few-electron single-crystal silicon quantum dots. NATURE NANOTECHNOLOGY 2010; 5:502-505. [PMID: 20495552 DOI: 10.1038/nnano.2010.95] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Accepted: 04/13/2010] [Indexed: 05/29/2023]
Abstract
A defining feature of modern CMOS devices and almost all quantum semiconductor devices is the use of many different materials. For example, although electrical conduction often occurs in single-crystal semiconductors, gates are frequently made of metals and dielectrics are commonly amorphous. Such devices have demonstrated remarkable improvements in performance over recent decades, but the heterogeneous nature of these devices can lead to defects at the interfaces between the different materials, which is a disadvantage for applications in spintronics and quantum information processing. Here we report the fabrication of a few-electron quantum dot in single-crystal silicon that does not contain any heterogeneous interfaces. The quantum dot is defined by atomically abrupt changes in the density of phosphorus dopant atoms, and the resulting confinement produces novel effects associated with energy splitting between the conduction band valleys. These single-crystal devices offer the opportunity to study how very sharp, atomic-scale confinement--which will become increasingly important for both classical and quantum devices--influences the operation and performance of devices.
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Affiliation(s)
- Martin Fuechsle
- Centre for Quantum Computer Technology, University of New South Wales, Sydney NSW 2052, Australia
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Bielejec E, Seamons JA, Carroll MS. Single ion implantation for single donor devices using Geiger mode detectors. NANOTECHNOLOGY 2010; 21:85201. [PMID: 20101077 DOI: 10.1088/0957-4484/21/8/085201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Electronic devices that are designed to use the properties of single atoms such as donors or defects have become a reality with recent demonstrations of donor spectroscopy, single photon emission sources, and magnetic imaging using defect centers in diamond. Ion implantation, an industry standard for atom placement in materials, requires augmentation for single ion capability including a method for detecting a single ion arrival. Integrating single ion detection techniques with the single donor device construction region allows single ion arrival to be assured. Improving detector sensitivity is linked to improving control over the straggle of the ion as well as providing more flexibility in lay-out integration with the active region of the single donor device construction zone by allowing ion sensing at potentially greater distances. Using a remotely located passively gated single ion Geiger mode avalanche diode (SIGMA) detector we have demonstrated 100% detection efficiency at a distance of >75 microm from the center of the collecting junction. This detection efficiency is achieved with sensitivity to approximately 600 or fewer electron-hole pairs produced by the implanted ion. Ion detectors with this sensitivity and integrated with a thin dielectric, for example a 5 nm gate oxide, using low energy Sb implantation would have an end of range straggle of <2.5 nm. Significant reduction in false count probability is, furthermore, achieved by modifying the ion beam set-up to allow for cryogenic operation of the SIGMA detector. Using a detection window of 230 ns at 1 Hz, the probability of a false count was measured as approximately 10(-1) and 10(-4) for operation temperatures of approximately 300 K and approximately 77 K, respectively. Low temperature operation and reduced false, 'dark', counts are critical to achieving high confidence in single ion arrival. For the device performance in this work, the confidence is calculated as a probability of >98% for counting one and only one ion for a false count probability of 10(-4) at an average ion number per gated window of 0.015.
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Affiliation(s)
- E Bielejec
- Sandia National Laboratories, PO Box 5800, Albuquerque, NM 87185-1056, USA
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Rogge S. Nanoelectronics: single dopants learn their place. NATURE NANOTECHNOLOGY 2010; 5:100-101. [PMID: 20130587 DOI: 10.1038/nnano.2010.11] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
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Scappucci G, Capellini G, Lee WCT, Simmons MY. Atomic-scale patterning of hydrogen terminated Ge(001) by scanning tunneling microscopy. NANOTECHNOLOGY 2009; 20:495302. [PMID: 19893153 DOI: 10.1088/0957-4484/20/49/495302] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In this paper we demonstrate atomic-scale lithography on hydrogen terminated Ge(001). The lithographic patterns were obtained by selectively desorbing hydrogen atoms from a H resist layer adsorbed on a clean, atomically flat Ge(001) surface with a scanning tunneling microscope tip operating in ultra-high vacuum. The influence of the tip-to-sample bias on the lithographic process have been investigated. Lithographic patterns with feature-sizes from 200 to 1.8 nm have been achieved by varying the tip-to-sample bias. These results open up the possibility of a scanning-probe lithography approach to the fabrication of future atomic-scale devices in germanium.
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Affiliation(s)
- G Scappucci
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
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Simmons CB, Thalakulam M, Rosemeyer BM, Van Bael BJ, Sackmann EK, Savage DE, Lagally MG, Joynt R, Friesen M, Coppersmith SN, Eriksson MA. Charge sensing and controllable tunnel coupling in a Si/SiGe double quantum dot. NANO LETTERS 2009; 9:3234-3238. [PMID: 19645459 DOI: 10.1021/nl9014974] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report integrated charge sensing measurements on a Si/SiGe double quantum dot. The quantum dot is shown to be tunable from a single, large dot to a well-isolated double dot. Charge sensing measurements enable the extraction of the tunnel coupling t between the quantum dots as a function of the voltage on the top gates defining the device. Control of the voltage on a single such gate tunes the barrier separating the two dots. The measured tunnel coupling is an exponential function of the gate voltage. The ability to control t is an important step toward controlling spin qubits in silicon quantum dots.
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Affiliation(s)
- C B Simmons
- University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
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