ORCID Profile
0000-0003-1649-823X
Current Organisations
Purdue University
,
University of New South Wales
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Condensed Matter Physics | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Quantum Optics | Quantum Information, Computation and Communication | Condensed Matter Modelling and Density Functional Theory |
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Physical Sciences | Scientific Instruments | Expanding Knowledge in Engineering | Expanding Knowledge in Technology
Related Links
Publications
Thickness Engineered Tunnel Field-Effect Transistors Based on Phosphorene
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2017
Valley dependent anisotropic spin splitting in silicon quantum dots
Publisher: Springer Science and Business Media LLC
Date: 05-06-2018
DOI: 10.1038/S41534-018-0075-1
Abstract: Spin qubits hosted in silicon (Si) quantum dots (QD) are attractive due to their exceptionally long coherence times and compatibility with the silicon transistor platform. To achieve electrical control of spins for qubit scalability, recent experiments have utilized gradient magnetic fields from integrated micro-magnets to produce an extrinsic coupling between spin and charge, thereby electrically driving electron spin resonance (ESR). However, spins in silicon QDs experience a complex interplay between spin, charge, and valley degrees of freedom, influenced by the atomic scale details of the confining interface. Here, we report experimental observation of a valley dependent anisotropic spin splitting in a Si QD with an integrated micro-magnet and an external magnetic field. We show by atomistic calculations that the spin-orbit interaction (SOI), which is often ignored in bulk silicon, plays a major role in the measured anisotropy. Moreover, inhomogeneities such as interface steps strongly affect the spin splittings and their valley dependence. This atomic-scale understanding of the intrinsic and extrinsic factors controlling the valley dependent spin properties is a key requirement for successful manipulation of quantum information in Si QDs.
Erratum: Lifetime-Enhanced Transport in Silicon due to Spin and Valley Blockade [Phys. Rev. Lett.107, 136602 (2011)]
Publisher: American Physical Society (APS)
Date: 23-01-2013
Nuclear spin induced decoherence of a quantum dot in Si confined at a SiGe interface: Decoherence dependence on 73Ge
Publisher: American Physical Society (APS)
Date: 11-05-2012
Spatially resolving valley quantum interference of a donor in silicon
Publisher: Springer Science and Business Media LLC
Date: 06-04-2014
DOI: 10.1038/NMAT3941
Abstract: Electron and nuclear spins of donor ensembles in isotopically pure silicon experience a vacuum-like environment, giving them extraordinary coherence. However, in contrast to a real vacuum, electrons in silicon occupy quantum superpositions of valleys in momentum space. Addressable single-qubit and two-qubit operations in silicon require that qubits are placed near interfaces, modifying the valley degrees of freedom associated with these quantum superpositions and strongly influencing qubit relaxation and exchange processes. Yet to date, spectroscopic measurements have only probed wavefunctions indirectly, preventing direct experimental access to valley population, donor position and environment. Here we directly probe the probability density of single quantum states of in idual subsurface donors, in real space and reciprocal space, using scanning tunnelling spectroscopy. We directly observe quantum mechanical valley interference patterns associated with linear superpositions of valleys in the donor ground state. The valley population is found to be within 5% of a bulk donor when 2.85 ± 0.45 nm from the interface, indicating that valley-perturbation-induced enhancement of spin relaxation will be negligible for depths greater than 3 nm. The observed valley interference will render two-qubit exchange gates sensitive to atomic-scale variations in positions of subsurface donors. Moreover, these results will also be of interest for emerging schemes proposing to encode information directly in valley polarization.
Universal Behavior of Atomistic Strain in Self-Assembled Quantum Dots
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2016
Silicon at the fundamental scaling limit-atomic-scale donor-based quantum electronics
Publisher: IEEE
Date: 06-2014
Hyperfine-mediated spin relaxation in donor-atom qubits in silicon
Publisher: American Physical Society (APS)
Date: 20-04-2023
The Use of Exchange Coupled Atom Qubits as Atomic‐Scale Magnetic Field Sensors (Adv. Mater. 6/2023)
Publisher: Wiley
Date: 02-2023
Bounds to electron spin qubit variability for scalable CMOS architectures
Publisher: Research Square Platform LLC
Date: 14-07-2023
DOI: 10.21203/RS.3.RS-3057916/V1
Abstract: Spins of electrons in CMOS quantum dots combine exquisite quantum properties and scalable fabrication. In the age of quantum technology, however, the metrics that crowned Si/SiO$_2$ as the microelectronics standard need to be reassessed with respect to their impact upon qubit performance. We chart spin qubit variability due to the unavoidable atomic-scale roughness of the Si/SiO$_2$ interface, compiling experiments across 12 devices, and develop theoretical tools to analyse these results. Atomistic tight binding and path integral Monte Carlo methods are adapted to describe fluctuations in devices with millions of atoms by directly analysing their wavefunctions and electron paths instead of their energy spectra. We correlate the effect of roughness with the variability in qubit position, deformation, valley splitting, valley phase, spin-orbit coupling and exchange coupling. These variabilities are found to be bounded, and they lie within the tolerances for scalable architectures for quantum computing as long as robust control methods are incorporated.
Spin-Lattice Relaxation Times of Single Donors and Donor Clusters in Silicon
Publisher: American Physical Society (APS)
Date: 11-12-2014
Coherent Control of a SingleSi
Publisher:
American Physical Society (APS)
Date:
09-12-2014
Publisher: American Physical Society (APS)
Date: 09-12-2014
Electron
g
Publisher: American Physical Society (APS)
Date: 15-01-2020
Polarization-Engineered III-Nitride Heterojunction Tunnel Field-Effect Transistors
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2015
Multi‐Scale Modeling of Tunneling in Nanoscale Atomically Precise Si:P Tunnel Junctions
Publisher: Wiley
Date: 08-03-2023
Abstract: Controlling electron tunneling is of fundamental importance in the design and operation of semiconductor nanostructures such as field effect transistors (FETs) and quantum computing device architectures. The exponential sensitivity of tunneling with distance requires precise fabrication techniques to engineer the desired device dimensions to achieve the appropriate tunneling resistances/tunnel rates. This is particularly important for high fidelity spin readout and qubit exchange in quantum computing architectures. Here, it is shown by combining precision fabrication techniques with accurate atomistic modeling, predictive device design criteria are achieved at atomic length scales. Such a tool is useful when devices become more complex or have arbitrary shapes/geometries. In particular, in this study, atomic precision patterning of monolayer degenerately phosphorus‐doped silicon tunnel junctions patterned by scanning tunnelling microscopy lithography and tight‐binding non‐equilibrium Green's function (TB‐NEGF) modeling is combined to describe the dependence of tunnel junction resistance R T on junction length. An agreement with experiment to within a factor of 2 over 4 orders of magnitude in R T is found, and this model allows to accurately determine the barrier height V 0 = 57.5 ± 1 meV and lateral seam s xy = 0.39 ± 0.01 nm in these nanoscale junctions. This study confirms the use of the TB‐NEGF formalism to accurately model highly doped atomically precise tunnel junctions in silicon. Further applications of this model will enable improved device performance at the nanoscale.
Atomic fluctuations lifting the energy degeneracy in Si/SiGe quantum dots
Publisher: Springer Science and Business Media LLC
Date: 13-12-2022
DOI: 10.1038/S41467-022-35458-0
Abstract: Electron spins in Si/SiGe quantum wells suffer from nearly degenerate conduction band valleys, which compete with the spin degree of freedom in the formation of qubits. Despite attempts to enhance the valley energy splitting deterministically, by engineering a sharp interface, valley splitting fluctuations remain a serious problem for qubit uniformity, needed to scale up to large quantum processors. Here, we elucidate and statistically predict the valley splitting by the holistic integration of 3D atomic-level properties, theory and transport. We find that the concentration fluctuations of Si and Ge atoms within the 3D landscape of Si/SiGe interfaces can explain the observed large spread of valley splitting from measurements on many quantum dot devices. Against the prevailing belief, we propose to boost these random alloy composition fluctuations by incorporating Ge atoms in the Si quantum well to statistically enhance valley splitting.
Shelving and latching spin readout in atom qubits in silicon
Publisher: American Physical Society (APS)
Date: 22-08-2022
Eigenvalue solvers for atomistic simulations of electronic structures with NEMO-3D
Publisher: Springer Science and Business Media LLC
Date: 22-02-2008
Limits to Quantum Gate Fidelity from Near-Field Thermal and Vacuum Fluctuations
Publisher: American Physical Society (APS)
Date: 12-06-2023
Atomically engineered electron spin lifetimes of 30 s in silicon
Publisher: American Association for the Advancement of Science (AAAS)
Date: 03-03-2017
Abstract: Atomic engineering of donor-based spin qubits results in long lifetimes and high-fidelity two-qubit readout.
Multiscale-multiphysics modeling of nonpolar InGaN LEDs
Publisher: IEEE
Date: 07-2017
Shallow dopant pairs in silicon: An atomistic full configuration interaction study
Publisher: American Physical Society (APS)
Date: 29-04-2022
Transport-based dopant metrology in advanced FinFETs
Publisher: IEEE
Date: 12-2008
Designing a large scale quantum computer with atomistic simulations
Publisher: IEEE
Date: 06-2014
Deep ultra-violet plasmonics: exploiting momentum-resolved electron energy loss spectroscopy to probe germanium
Publisher: Optica Publishing Group
Date: 31-03-2022
DOI: 10.1364/OE.447017
Abstract: Germanium is typically used for solid-state electronics, fiber-optics, and infrared applications, due to its semiconducting behavior at optical and infrared wavelengths. In contrast, here we show that the germanium displays metallic nature and supports propagating surface plasmons in the deep ultraviolet (DUV) wavelengths, that is typically not possible to achieve with conventional plasmonic metals such as gold, silver, and aluminum. We measure the photonic band spectrum and distinguish the plasmonic excitation modes: bulk plasmons, surface plasmons, and Cherenkov radiation using a momentum-resolved electron energy loss spectroscopy. The observed spectrum is validated through the macroscopic electrodynamic electron energy loss theory and first-principles density functional theory calculations. In the DUV regime, intraband transitions of valence electrons dominate over the interband transitions, resulting in the observed highly dispersive surface plasmons. We further employ these surface plasmons in germanium to design a DUV radiation source based on the Smith-Purcell effect. Our work opens a new frontier of DUV plasmonics to enable the development of DUV devices such as metasurfaces, detectors, and light sources based on plasmonic germanium thin films.
High Precision Quantum Control of Single Donor Spins in Silicon
Publisher: American Physical Society (APS)
Date: 20-07-2007
Scaling Theory of Electrically Doped 2D Transistors
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2015
Atomistic simulation of steep subthreshold slope Bi-layer MoS<inf>2</inf> transistors
Publisher: IEEE
Date: 06-2014
Nonadiabatic quantum control of valley states in silicon
Publisher: American Physical Society (APS)
Date: 07-02-2022
+Level Spectrum Of Single Gated As Donors
Publisher: AIP
Date: 2010
DOI: 10.1063/1.3295570
Valley Filtering in Spatial Maps of Coupling between Silicon Donors and Quantum Dots
Publisher: American Physical Society (APS)
Date: 27-08-2018
Transport of spin qubits with donor chains under realistic experimental conditions
Publisher: American Physical Society (APS)
Date: 25-07-2016
Two-electron states of a group-V donor in silicon from atomistic full configuration interactions
Publisher: American Physical Society (APS)
Date: 02-05-2018
Carrier leakage in Ge/Si core-shell nanocrystals for lasers: core size and strain effects
Publisher: SPIE
Date: 08-09-2011
DOI: 10.1117/12.894153
Spin-Valley Locking for In-Gap Quantum Dots in a MoS2 Transistor
Publisher: American Chemical Society (ACS)
Date: 26-06-2023
Publisher’s Note: Engineered valley-orbit splittings in quantum-confined nanostructures in silicon [Phys. Rev. B83, 195323 (2011)]
Publisher: American Physical Society (APS)
Date: 15-06-2011
Silicon quantum processor with robust long-distance qubit couplings
Publisher: Springer Science and Business Media LLC
Date: 06-09-2017
DOI: 10.1038/S41467-017-00378-X
Abstract: Practical quantum computers require a large network of highly coherent qubits, interconnected in a design robust against errors. Donor spins in silicon provide state-of-the-art coherence and quantum gate fidelities, in a platform adapted from industrial semiconductor processing. Here we present a scalable design for a silicon quantum processor that does not require precise donor placement and leaves le space for the routing of interconnects and readout devices. We introduce the flip-flop qubit, a combination of the electron-nuclear spin states of a phosphorus donor that can be controlled by microwave electric fields. Two-qubit gates exploit a second-order electric dipole-dipole interaction, allowing selective coupling beyond the nearest-neighbor, at separations of hundreds of nanometers, while microwave resonators can extend the entanglement to macroscopic distances. We predict gate fidelities within fault-tolerance thresholds using realistic noise models. This design provides a realizable blueprint for scalable spin-based quantum computers in silicon.
A many-electron tight binding method for the analysis of quantum dot systems
Publisher: AIP Publishing
Date: 12-2012
DOI: 10.1063/1.4759256
Abstract: We present a method which computes many-electron energies and eigenfunctions by a full configuration interaction, which uses a basis of atomistic tight-binding wave functions. This approach captures electron correlation as well as atomistic effects, and is well suited to solid state quantum dot systems containing few electrons, where valley physics and disorder contribute significantly to device behavior. Results are reported for a two-electron silicon double quantum dot as an ex le.
Optimization of the anharmonic strain model to capture realistic strain distributions in quantum dots
Publisher: IEEE
Date: 08-2014
SiGe quantum wells with oscillating Ge concentrations for quantum dot qubits
Publisher: Springer Science and Business Media LLC
Date: 15-12-2022
DOI: 10.1038/S41467-022-35510-Z
Abstract: Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings of the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance the valley splitting rely on sharp interfaces or modifications in the quantum well barriers that can be difficult to grow. Here, we propose and demonstrate a new heterostructure, the “Wiggle Well”, whose key feature is Ge concentration oscillations inside the quantum well. Experimentally, we show that placing Ge in the quantum well does not significantly impact our ability to form and manipulate single-electron quantum dots. We further observe large and widely tunable valley splittings, from 54 to 239 μ eV. Tight-binding calculations, and the tunability of the valley splitting, indicate that these results can mainly be attributed to random concentration fluctuations that are lified by the presence of Ge alloy in the heterostructure, as opposed to a deterministic enhancement due to the concentration oscillations. Quantitative predictions for several other heterostructures point to the Wiggle Well as a robust method for reliably enhancing the valley splitting in future qubit devices.
Aharonov–Bohm interference of fractional quantum Hall edge modes
Publisher: Springer Science and Business Media LLC
Date: 04-03-2019
Engineered valley-orbit splittings in quantum-confined nanostructures in silicon
Publisher: American Physical Society (APS)
Date: 26-05-2011
Dielectric Engineered Tunnel Field-Effect Transistor
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2015
A predictive analytic model for high-performance tunneling field-effect transistors approaching non-equilibrium Green's function simulations
Publisher: AIP Publishing
Date: 28-10-2015
DOI: 10.1063/1.4934682
Abstract: A new compact modeling approach is presented which describes the full current-voltage (I-V) characteristic of high-performance (aggressively scaled-down) tunneling field-effect-transistors (TFETs) based on homojunction direct-bandgap semiconductors. The model is based on an analytic description of two key features, which capture the main physical phenomena related to TFETs: (1) the potential profile from source to channel and (2) the elliptic curvature of the complex bands in the bandgap region. It is proposed to use 1D Poisson's equations in the source and the channel to describe the potential profile in homojunction TFETs. This allows to quantify the impact of source/drain doping on device performance, an aspect usually ignored in TFET modeling but highly relevant in ultra-scaled devices. The compact model is validated by comparison with state-of-the-art quantum transport simulations using a 3D full band atomistic approach based on non-equilibrium Green's functions. It is shown that the model reproduces with good accuracy the data obtained from the simulations in all regions of operation: the on/off states and the n branches of conduction. This approach allows calculation of energy-dependent band-to-band tunneling currents in TFETs, a feature that allows gaining deep insights into the underlying device physics. The simplicity and accuracy of the approach provide a powerful tool to explore in a quantitatively manner how a wide variety of parameters (material-, size-, and/or geometry-dependent) impact the TFET performance under any bias conditions. The proposed model presents thus a practical complement to computationally expensive simulations such as the 3D NEGF approach.
Configurable Electrostatically Doped High Performance Bilayer Graphene Tunnel FET
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2016
Innovative characterization techniques for ultra-scaled FinFETs
Publisher: IEEE
Date: 08-2010
Charge sensed Pauli blockade in a metal-oxide-semiconductor lateral double quantum dot
Publisher: American Chemical Society (ACS)
Date: 18-11-2013
DOI: 10.1021/NL4020759
Abstract: We report Pauli blockade in a multielectron silicon metal-oxide-semiconductor double quantum dot with an integrated charge sensor. The current is rectified up to a blockade energy of 0.18 ± 0.03 meV. The blockade energy is analogous to singlet-triplet splitting in a two electron double quantum dot. Built-in imbalances of tunnel rates in the MOS DQD obfuscate some edges of the bias triangles. A method to extract the bias triangles is described, and a numeric rate-equation simulation is used to understand the effect of tunneling imbalances and finite temperature on charge stability (honeycomb) diagram, in particular the identification of missing and shifting edges. A bound on relaxation time of the triplet-like state is also obtained from this measurement.
Electron spin relaxation of single phosphorus donors and donor clusters in atomically engineered silicon devices
Publisher: IEEE
Date: 06-2017
Orbital Stark effect and quantum confinement transition of donors in silicon
Publisher: American Physical Society (APS)
Date: 09-10-2009
Theoretical study of strain-dependent optical absorption in a doped self-assembled InAs/InGaAs/GaAs/AlGaAs quantum dot
Publisher: Beilstein Institut
Date: 04-04-2018
DOI: 10.3762/BJNANO.9.99
Abstract: A detailed theoretical study of the optical absorption in doped self-assembled quantum dots is presented. A rigorous atomistic strain model as well as a sophisticated 20-band tight-binding model are used to ensure accurate prediction of the single particle states in these devices. We also show that for doped quantum dots, many-particle configuration interaction is also critical to accurately capture the optical transitions of the system. The sophisticated models presented in this work reproduce the experimental results for both undoped and doped quantum dot systems. The effects of alloy mole fraction of the strain controlling layer and quantum dot dimensions are discussed. Increasing the mole fraction of the strain controlling layer leads to a lower energy gap and a larger absorption wavelength. Surprisingly, the absorption wavelength is highly sensitive to the changes in the diameter, but almost insensitive to the changes in dot height. This behavior is explained by a detailed sensitivity analysis of different factors affecting the optical transition energy.
Practical strategies for enhancing the valley splitting in Si/SiGe quantum wells
Publisher: American Physical Society (APS)
Date: 05-09-2023
Addressable electron spin resonance using donors and donor molecules in silicon
Publisher: American Association for the Advancement of Science (AAAS)
Date: 06-07-2018
Abstract: Built-in hyperfine couplings of donor qubits engineered by precision placement promote addressable electron spin resonance.
Coherent electron transport by adiabatic passage in an imperfect donor chain
Publisher: American Physical Society (APS)
Date: 18-10-2010
Combination of Equilibrium and Nonequilibrium Carrier Statistics Into an Atomistic Quantum Transport Model for Tunneling Heterojunctions
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2017
Statistical modeling of ultra-scaled donor-based silicon phosphorus devices
Publisher: IEEE
Date: 06-2014
Engineering the optical transitions of self-assembled quantum dots
Publisher: IEEE
Date: 09-2015
Spatially resolved resonant tunneling on single atoms in silicon
Publisher: IOP Publishing
Date: 18-03-2015
DOI: 10.1088/0953-8984/27/15/154203
Abstract: The ability to control single dopants in solid-state devices has opened the way towards reliable quantum computation schemes. In this perspective it is essential to understand the impact of interfaces and electric fields, inherent to address coherent electronic manipulation, on the dopants atomic scale properties. This requires both fine energetic and spatial resolution of the energy spectrum and wave-function, respectively. Here we present an experiment fulfilling both conditions: we perform transport on single donors in silicon close to a vacuum interface using a scanning tunneling microscope (STM) in the single electron tunneling regime. The spatial degrees of freedom of the STM tip provide a versatility allowing a unique understanding of electrostatics. We obtain the absolute energy scale from the thermal broadening of the resonant peaks, allowing us to deduce the charging energies of the donors. Finally we use a rate equations model to derive the current in presence of an excited state, highlighting the benefits of the highly tunable vacuum tunnel rates which should be exploited in further experiments. This work provides a general framework to investigate dopant-based systems at the atomic scale.
Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory
Publisher: IOP Publishing
Date: 18-03-2015
DOI: 10.1088/0953-8984/27/15/154207
Abstract: Atomistic tight-binding (TB) simulations are performed to calculate the Stark shift of the hyperfine coupling for a single arsenic (As) donor in silicon (Si). The role of the central-cell correction is studied by implementing both the static and the non-static dielectric screenings of the donor potential, and by including the effect of the lattice strain close to the donor site. The dielectric screening of the donor potential tunes the value of the quadratic Stark shift parameter (η2) from -1.3 × 10(-3) µm(2) V(-2) for the static dielectric screening to -1.72 × 10(-3) µm(2) V(-2) for the non-static dielectric screening. The effect of lattice strain, implemented by a 3.2% change in the As-Si nearest-neighbour bond length, further shifts the value of η2 to -1.87 × 10(-3) µm(2) V(-2), resulting in an excellent agreement of theory with the experimentally measured value of -1.9 ± 0.2 × 10(-3) µm(2) V(-2). Based on our direct comparison of the calculations with the experiment, we conclude that the previously ignored non-static dielectric screening of the donor potential and the lattice strain significantly influence the donor wave function charge density and thereby leads to a better agreement with the available experimental data sets.
Interface-induced spin-orbit interaction in silicon quantum dots and prospects for scalability
Publisher: American Physical Society (APS)
Date: 04-06-2018
III-N heterostructure devices for low-power logic
Publisher: IEEE
Date: 03-2017
Atomistic simulations of adiabatic coherent electron transport in triple donor systems
Publisher: American Physical Society (APS)
Date: 07-07-2009
Novel characterization of dopant-based qubits
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Electronic states of Ge/Si nanocrystals with crescent-shaped Ge-cores
Publisher: AIP Publishing
Date: 15-07-2012
DOI: 10.1063/1.4739715
Abstract: Ge/Si nanocrystals can serve as charge storage sites in a nanocrystal memory by providing a hole quantum-well in the Ge region. The electronic states of realistically shaped Ge/Si nanocrystals with crescent-shaped Ge-cores are calculated to determine the hole confinement energies, effective masses, barrier heights, and thermionic lifetimes. As the Ge crescent thickness increases from 1 nm to 3.5 nm, the hole confinement energy decreases from 0.52 to 0.28 eV, the barrier height to escape into the Si valence band increases from 0.25 to 0.51 eV, and the resulting thermionic hole lifetime increases from 10−9 to 10−5 s. The nanocrystals are modeled with an atomistic, 20-band sp3d5s* tight-binding model including spin-orbit coupling as implemented in NEMO3D. Geometry relaxation and strain are included using the valence-force-field model with Keating potentials.
Author Correction: Ab-initio calculations of shallow dopant qubits in silicon from pseudopotential and all-electron mixed approach
Publisher: Springer Science and Business Media LLC
Date: 22-09-2022
Determination of the eigenstates and wavefunctions of a single gated As donor
Publisher: IEEE
Date: 02-2008
Electric field reduced charging energies and two-electron bound excited states of single donors in silicon
Publisher: American Physical Society (APS)
Date: 19-09-2011
Atomistic Simulation of Realistically Sized Nanodevices Using NEMO 3-D—Part I: Models and Benchmarks
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2007
Core size dependence of the confinement energies, barrier heights, and hole lifetimes in Ge-core/Si-shell nanocrystals
Publisher: AIP Publishing
Date: 10-2011
DOI: 10.1063/1.3642970
Abstract: The effect of the Ge core size on the confinement energies, barrier heights, and hole lifetimes in spherical Ge/Si core-shell nanocrystals is studied using an atomistic, tight-binding model with an sp3d5s* basis including spin-orbit coupling. Nanocrystal diameters range from 11 nm to 17.5 nm with Ge core diameters ranging from 1 nm to 7.5 nm. With a Ge core diameter of ~4 nm, and a Si shell thickness of ≥3 nm, the thermionic barrier presented by the Si shell increases the hole lifetime by a factor of ~2×108 compared to the hole lifetime in an all-Si nanocrystal in SiO2. A retention lifetime of 10 years is obtained with a 3 nm Ge core and a 3 nm Si shell with a 3 nm SiO2 tunnel oxide.
Direct Observation of 2D Electrostatics and Ohmic Contacts in Template-Grown Graphene/WS2 Heterostructures
Publisher: American Chemical Society (ACS)
Date: 27-02-2017
Sensitivity Challenge of Steep Transistors
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2018
Design Rules for High Performance Tunnel Transistors From 2-D Materials
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2016
Ab-initio calculations of shallow dopant qubits in silicon from pseudopotential and all-electron mixed approach
Publisher: Springer Science and Business Media LLC
Date: 27-06-2022
DOI: 10.1038/S42005-022-00948-6
Abstract: Obtaining an accurate first-principle description of the electronic properties of dopant qubits is critical for engineering and optimizing high-performance quantum computing. However, density functional theory (DFT) has had limited success in providing a full quantitative description of these dopants due to their large wavefunction extent. Here, we build on recent advances in DFT to evaluate phosphorus dopants in silicon on a lattice comprised of 4096 atoms with hybrid functionals on a pseudopotential and all-electron mixed approach. Remarkable agreement is achieved with experimental measurements including: the electron-nuclear hyperfine coupling (115.5 MHz) and its electric field response (−2.65 × 10 −3 μm 2 /V 2 ), the binding energy (46.07 meV), excited valley-orbital energies of 1sT 2 (37.22 meV) and 1sE (35.87 meV) states, and super-hyperfine couplings of the proximal shells of the silicon lattice. This quantitative description of spin and orbital properties of phosphorus dopant simultaneously from a single theoretical framework will help as a predictive tool for the design of qubits.
Tunnel Field-Effect Transistors in 2-D Transition Metal Dichalcogenide Materials
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2015
Spin blockade and exchange in Coulomb-confined silicon double quantum dots
Publisher: Springer Science and Business Media LLC
Date: 13-04-2014
Abstract: Electron spins confined to phosphorus donors in silicon are promising candidates as qubits because of their long coherence times, exceeding seconds in isotopically purified bulk silicon. With the recent demonstrations of initialization, readout and coherent manipulation of in idual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling in two tunnel-coupled phosphorus donors. Spin-to-charge conversion via Pauli spin blockade, an essential ingredient for reading out in idual spin states, is challenging in donor-based systems due to the inherently large donor charging energies (∼45 meV), requiring large electric fields (>1 MV m(-1)) to transfer both electron spins onto the same donor. Here, in a carefully characterized double donor-dot device, we directly observe spin blockade of the first few electrons and measure the effective exchange interaction between electron spins in coupled Coulomb-confined systems.
Materials and device simulations for silicon qubit design and optimization
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Symmetry Breaking and Fine Structure Splitting in Zincblende Quantum Dots: Atomistic Simulations of Long-Range Strain and Piezoelectric Field
Publisher: AIP
Date: 2007
DOI: 10.1063/1.2730157
Electrically controlling single-spin qubits in a continuous microwave field
Publisher: American Association for the Advancement of Science (AAAS)
Date: 03-04-2015
Abstract: Control of in idual spin qubits through local electric fields, suitable for large-scale silicon quantum computers.
Optimization of edge state velocity in the integer quantum Hall regime
Publisher: American Physical Society (APS)
Date: 05-02-2018
Extreme ultraviolet plasmonics and Cherenkov radiation in silicon
Publisher: The Optical Society
Date: 07-12-2018
Interface-induced heavy-hole/light-hole splitting of acceptors in silicon
Publisher: AIP Publishing
Date: 18-05-2015
DOI: 10.1063/1.4921640
Abstract: The energy spectrum of spin-orbit coupled states of in idual sub-surface boron acceptor dopants in silicon have been investigated using scanning tunneling spectroscopy at cryogenic temperatures. The spatially resolved tunnel spectra show two resonances, which we ascribe to the heavy- and light-hole Kramers doublets. This type of broken degeneracy has recently been argued to be advantageous for the lifetime of acceptor-based qubits [R. Ruskov and C. Tahan, Phys. Rev. B 88, 064308 (2013)]. The depth dependent energy splitting between the heavy- and light-hole Kramers doublets is consistent with tight binding calculations, and is in excess of 1 meV for all acceptors within the experimentally accessible depth range (& nm from the surface). These results will aid the development of tunable acceptor-based qubits in silicon with long coherence times and the possibility for electrical manipulation.
Electrically doped WTe<inf>2</inf> tunnel transistors
Publisher: IEEE
Date: 09-2015
Electrically doped 2D material tunnel transistor
Publisher: IEEE
Date: 09-2015
Spin-Photon Coupling for Atomic Qubit Devices in Silicon
Publisher: American Physical Society (APS)
Date: 04-05-2022
Flopping-Mode Electric Dipole Spin Resonance in Phosphorus Donor Qubits in Silicon
Publisher: American Physical Society (APS)
Date: 04-05-2022
Channel Thickness Optimization for Ultrathin and 2-D Chemically Doped TFETs
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2018
Strain and electric field control of hyperfine interactions for donor spin qubits in silicon
Publisher: American Physical Society (APS)
Date: 25-06-2015
Spin readout and addressability of phosphorus-donor clusters in silicon
Publisher: Springer Science and Business Media LLC
Date: 18-06-2013
DOI: 10.1038/NCOMMS3017
Abstract: The spin states of an electron bound to a single phosphorus donor in silicon show remarkably long coherence and relaxation times, which makes them promising building blocks for the realization of a solid-state quantum computer. Here we demonstrate, by high-fidelity (93%) electrical spin readout, that a long relaxation time T1 of about 2 s, at B=1.2 T and T≈100 mK, is also characteristic of electronic spin states associated with a cluster of few phosphorus donors, suggesting their suitability as hosts for spin qubits. Owing to the difference in the hyperfine coupling, electronic spin transitions of such clusters can be sufficiently distinct from those of a single phosphorus donor. Our atomistic tight-binding calculations reveal that when neighbouring qubits are hosted by a single phosphorus atom and a cluster of two phosphorus donors, the difference in their electron spin resonance frequencies allows qubit rotations with error rates ≈10(-4). These results provide a new approach to achieving in idual qubit addressability.
Effect of strain on the electronic and optical properties of Ge–Si dome shaped nanocrystals
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CP03711A
Abstract: An atomistic study of Ge-core–Si-shell nanocrystals gives a detailed picture of how strain and confinement effect the electronic and optical properties.
Efficient and stable piezo-photocatalytic splitting of water and seawater by interfacial engineering of Na0.5Bi0.5TiO3/Na0.5Bi4.5Ti4O15 self-generated heterojunctions
Publisher: Elsevier BV
Date: 11-2023
Electrically Tunable Bandgaps in Bilayer MoS2
Publisher: American Chemical Society (ACS)
Date: 13-11-2015
DOI: 10.1021/ACS.NANOLETT.5B03218
Abstract: Artificial semiconductors with manufactured band structures have opened up many new applications in the field of optoelectronics. The emerging two-dimensional (2D) semiconductor materials, transition metal dichalcogenides (TMDs), cover a large range of bandgaps and have shown potential in high performance device applications. Interestingly, the ultrathin body and anisotropic material properties of the layered TMDs allow a wide range modification of their band structures by electric field, which is obviously desirable for many nanoelectronic and nanophotonic applications. Here, we demonstrate a continuous bandgap tuning in bilayer MoS2 using a dual-gated field-effect transistor (FET) and photoluminescence (PL) spectroscopy. Density functional theory (DFT) is employed to calculate the field dependent band structures, attributing the widely tunable bandgap to an interlayer direct bandgap transition. This unique electric field controlled spontaneous bandgap modulation approaching the limit of semiconductor-to-metal transition can open up a new field of not yet existing applications.
Dramatic Impact of Dimensionality on the Electrostatics of P-N Junctions and Its Sensing and Switching Applications
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2018
Switching Mechanism and the Scalability of Vertical-TFETs
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2018
Gate-inducedg
Publisher: American Physical Society (APS)
Date: 10-2009
WSe2 Homojunction Devices: Electrostatically Configurable as Diodes, MOSFETs, and Tunnel FETs for Reconfigurable Computing
Publisher: Wiley
Date: 25-08-2019
Abstract: In this paper, electrostatically configurable 2D tungsten diselenide (WSe
Lifetime-Enhanced Transport in Silicon due to Spin and Valley Blockade
Publisher: American Physical Society (APS)
Date: 19-09-2011
Exchange Coupling in a Linear Chain of Three Quantum-Dot Spin Qubits in Silicon
Publisher: American Chemical Society (ACS)
Date: 22-01-2021
Noninvasive Spatial Metrology of Single-Atom Devices
Publisher: American Chemical Society (ACS)
Date: 18-04-2013
DOI: 10.1021/NL303863S
Abstract: The exact location of a single dopant atom in a nanostructure can influence or fully determine the functionality of highly scaled transistors or spin-based devices. We demonstrate here a noninvasive spatial metrology technique, based on the microscopic modeling of three electrical measurements on a single-atom (phosphorus in silicon) spin qubit device: hyperfine coupling, ground state energy, and capacitive coupling to nearby gates. This technique allows us to locate the qubit atom with a precision of ±2.5 nm in two directions and ±15 nm in the third direction, which represents a 1500-fold improvement with respect to the prefabrication statistics obtainable from the ion implantation parameters.
A low resistance and stable lithium-garnet electrolyte interface enabled by a multifunctional anode additive for solid-state lithium batteries
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1TA07804F
Abstract: Limited reaction between Li 0.3 La 0.5 TiO 3 and molten lithium sufficiently modifies the properties of the lithium anode, improving the overall performance of solid-state lithium batteries.
Transport spectroscopy of a single atom in a FinFET
Publisher: IOP Publishing
Date: 03-2008
Achieving a higher performance in bilayer graphene FET - strain engineering
Publisher: IEEE
Date: 09-2015
Spin–orbit coupling in silicon for electrons bound to donors
Publisher: Springer Science and Business Media LLC
Date: 23-11-2018
DOI: 10.1038/S41534-018-0111-1
Abstract: Spin–orbit coupling (SOC) is fundamental to a wide range of phenomena in condensed matter, spanning from a renormalisation of the free-electron g -factor, to the formation of topological insulators, and Majorana Fermions. SOC has also profound implications in spin-based quantum information, where it is known to limit spin lifetimes ( T 1 ) in the inversion asymmetric semiconductors such as GaAs. However, for electrons in silicon—and in particular those bound to phosphorus donor qubits—SOC is usually regarded weak, allowing for spin lifetimes of minutes in the bulk. Surprisingly, however, in a nanoelectronic device donor spin lifetimes have only reached values of seconds. Here, we reconcile this difference by demonstrating that electric field induced SOC can dominate spin relaxation of donor-bound electrons. Eliminating this lifetime-limiting effect by careful alignment of an external vector magnetic field in an atomically engineered device, allows us to reach the bulk-limit of spin-relaxation times. Given the unexpected strength of SOC in the technologically relevant silicon platform, we anticipate that our results will stimulate future theoretical and experimental investigation of phenomena that rely on strong magnetoelectric coupling of atomically confined spins.
From Fowler–Nordheim to Nonequilibrium Green’s Function Modeling of Tunneling
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2016
Gate-induced quantum-confinement transition of a single dopant atom in a silicon FinFET
Publisher: Springer Science and Business Media LLC
Date: 15-06-2008
DOI: 10.1038/NPHYS994
2D tunnel transistors for ultra-low power applications: Promises and challenges
Publisher: IEEE
Date: 10-2015
Valley interference and spin exchange at the atomic scale in silicon
Publisher: Springer Science and Business Media LLC
Date: 30-11-2020
DOI: 10.1038/S41467-020-19835-1
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.
Valley population of donor states in highly strained silicon
Publisher: IOP Publishing
Date: 06-04-2022
Abstract: Strain is extensively used to controllably tailor the electronic properties of materials. In the context of indirect band-gap semiconductors such as silicon, strain lifts the valley degeneracy of the six conduction band minima, and by extension the valley states of electrons bound to phosphorus donors. Here, single phosphorus atoms are embedded in an engineered thin layer of silicon strained to 0.8% and their wave function imaged using spatially resolved spectroscopy. A prevalence of the out-of-plane valleys is confirmed from the real-space images, and a combination of theoretical modelling tools is used to assess how this valley repopulation effect can yield isotropic exchange and tunnel interactions in the xy -plane relevant for atomically precise donor qubit devices. Finally, the residual presence of in-plane valleys is evidenced by a Fourier analysis of both experimental and theoretical images, and atomistic calculations highlight the importance of higher orbital excited states to obtain a precise relationship between valley population and strain. Controlling the valley degree of freedom in engineered strained epilayers provides a new competitive asset for the development of donor-based quantum technologies in silicon.
Can Homojunction Tunnel FETs Scale Below 10 nm?
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2016
Stark tuning of the charge states of a two-donor molecule in silicon
Publisher: IOP Publishing
Date: 04-2011
DOI: 10.1088/0957-4484/22/22/225202
Abstract: A singly ionized two-donor molecule in silicon is an interesting test-bed system for implementing a quantum bit using charge degrees of freedom at the atomic limit of device fabrication. The operating principles of such a device are based on wavefunction symmetries defined by charge localizations and energy gaps in the spectrum. The Stark-shifted electronic structure of a two-donor phosphorus molecule is investigated using a multi-million-atom tight-binding framework. The effects of surface (S) and barrier (B) gates are analyzed for various voltage regimes. It is found that gate control is smooth for any donor separation, although at certain donor orientations the S and B gates may alter in functionality. Effects such as interface ionization, saturation of the lowest energy gap, and sensitivity to donor and gate placements are also investigated. Excited molecular states of P(2) + are found to impose limits on the allowed donor separations and operating gate voltages for coherent operation. This work therefore outlines and analyzes the various issues that are of importance in the design and control of such donor molecular systems.
Alloy Engineered Nitride Tunneling Field-Effect Transistor: A Solution for the Challenge of Heterojunction TFETs
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2019
Mapping Donor Electron Wave Function Deformations at a Sub-Bohr Orbit Resolution
Publisher: American Physical Society (APS)
Date: 04-09-2009
Optimisation of electron spin qubits in electrically driven multi-donor quantum dots
Publisher: Springer Science and Business Media LLC
Date: 04-11-2022
DOI: 10.1038/S41534-022-00646-9
Abstract: Multi-donor quantum dots have been at the forefront of recent progress in Si-based quantum computation. Among them, 2 P : 1 P spin qubits have a built-in dipole moment, making them ideal for electron dipole spin resonance (EDSR) using the donor hyperfine interaction, and thus all-electrical spin operation. We report fast EDSR, with T π ~ 10 − 50 ns and a Rabi ratio ( T 1 / T π ) ~ 10 6 . The fastest EDSR time T π occurs when the 2 P : 1 P axis is ∥ [111], while the best Rabi ratio occurs when it is ∥ [100]. Sensitivity to random telegraph noise due to nearby charge defects depends strongly on the location of the nearby defects. The qubit is robust against 1/ f noise provided it is operated away from the charge anti-crossing. Entanglement via exchange is several orders of magnitude faster than dipole-dipole coupling. These findings pave the way towards fast, low-power, coherent and scalable donor dot-based quantum computing.
The sub-band structure of atomically sharp dopant profiles in silicon
Publisher: Springer Science and Business Media LLC
Date: 06-2020
DOI: 10.1038/S41535-020-0237-1
Abstract: The downscaling of silicon-based structures and proto-devices has now reached the single-atom scale, representing an important milestone for the development of a silicon-based quantum computer. One especially notable platform for atomic-scale device fabrication is the so-called Si:P δ -layer, consisting of an ultra-dense and sharp layer of dopants within a semiconductor host. Whilst several alternatives exist, it is on the Si:P platform that many quantum proto-devices have been successfully demonstrated. Motivated by this, both calculations and experiments have been dedicated to understanding the electronic structure of the Si:P δ -layer platform. In this work, we use high-resolution angle-resolved photoemission spectroscopy to reveal the structure of the electronic states which exist because of the high dopant density of the Si:P δ -layer. In contrast to published theoretical work, we resolve three distinct bands, the most occupied of which shows a large anisotropy and significant deviation from simple parabolic behaviour. We investigate the possible origins of this fine structure, and conclude that it is primarily a consequence of the dielectric constant being large (ca. double that of bulk Si). Incorporating this factor into tight-binding calculations leads to a major revision of band structure specifically, the existence of a third band, the separation of the bands, and the departure from purely parabolic behaviour. This new understanding of the band structure has important implications for quantum proto-devices which are built on the Si:P δ -layer platform.
Voltage controlled exchange energies of a two-electron silicon double quantum dot with and without charge defects in the dielectric
Publisher: American Physical Society (APS)
Date: 20-03-2012
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