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Atomic-layer doping of SiGe heterostructures for atomic-precision donor devices

Physical Review Materials

Bussmann, Ezra B.; Gamble, John K.; Koepke, Justin K.; Laroche, D.; Huang, S.H.; Chuang, Y.; Li, J.Y.; Liu, C.W.; Swartzentruber, Brian S.; Lilly, M.P.; Carroll, Malcolm; Lu, Tzu-Ming L.

As a first step to porting scanning tunneling microscopy methods of atomic-precision fabrication to a strained-Si/SiGe platform, we demonstrate post-growth P atomic-layer doping of SiGe heterostructures. To preserve the substrate structure and elastic state, we use a T≤800 ° C process to prepare clean Si0.86Ge0.14 surfaces suitable for atomic-precision fabrication. P-saturated atomic-layer doping is incorporated and capped with epitaxial Si under a thermal budget compatible with atomic-precision fabrication. Hall measurements at T=0.3 K show that the doped heterostructure has R□=570±30Ω, yielding an electron density ne=2.1±0.1×1014cm-2 and mobility μe=52±3cm2V-1s-1, similar to saturated atomic-layer doping in pure Si and Ge. The magnitude of μe and the complete absence of Shubnikov-de Haas oscillations in magnetotransport measurements indicate that electrons are overwhelmingly localized in the donor layer, and not within a nearby buried Si well. This conclusion is supported by self-consistent Schrödinger-Poisson calculations that predict electron occupation primarily in the donor layer.

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TYPE Journal Article YEAR 2018
ScopusOSTIDOI

Enhancement-mode two-channel triple quantum dot from an undoped Si/Si0.8Ge0.2 quantum well hetero-structure

Applied Physics Letters

Studenikin, S.A.S.; Gaudreau, L.G.; Kataoka, K.K.; Austing, D.G.A.; Lu, Tzu-Ming L.; Luhman, Dwight R.; Bethke, Donald T.; Wanke, Michael W.; Lilly, Michael L.; Carroll, Malcolm; Sachrajda, A.S.S.

Here, we demonstrate coupled triple dot operation and charge sensing capability for the recently introduced quantum dot technology employing undoped Si/Si0.8Ge0.2 hetero-structures which also incorporate a single metal-gate layer to simplify fabrication. Si/SiGe hetero-structures with a Ge concentration of 20% rather than the more usual 30% typically encountered offer higher electron mobility. The devices consist of two in-plane parallel electron channels that host a double dot in one channel and a single dot in the other channel. In a device where the channels are sufficiently close a triple dot in a triangular configuration is induced leading to regions in the charge stability diagram where three charge-addition lines of different slope approach each other and anti-cross. In a device where the channels are further apart, the single dot charge-senses the double dot with relative change of ~2% in the sensor current.

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TYPE Journal Article YEAR 2018
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Silicon Qubits

Library Journal

Carroll, Malcolm; Ladd, Thaddeus L.

There are two good reasons to attempt to build quantum bits (qubits) out of silicon. The first is the obvious foundation of classical microelectronics. Although silicon quantum computers would operate in a fundamentally different way from classical computers$-$for example, at cryogenic temperatures$-$still the level of development in material quality, crystal growth, and fabrication methodologies for silicon is unrivaled by any other material in the world. Leveraging even a small fraction of the worldwide investment in silicon for qubit development could potentially put silicon-based qubits far ahead of other solid-state alternatives. The second, less obvious reason for choosing silicon is the remarkably clean magnetic environment witnessed by spins in highly purified and isotopically enriched silicon material. Fortuitously, 95.3% of the naturally occurring isotopes of Si nuclei (28Si and 30Si) are spin-0. These nuclei therefore have a “closed shell” of nuclear moments, providing no external magnetic field whatsoever. Add to this the possibility of intrinsic silicon with part-per-billion chemical quality and the system is remarkably close to “vacuum” with respect to magnetic noise properties.

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TYPE Journal Article YEAR 2018
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All-electrical universal control of a double quantum dot qubit in silicon MOS

Technical Digest - International Electron Devices Meeting, IEDM

Harvey-Collard, Patrick; Jock, Ryan M.; Jacobson, Noah T.; Baczewski, Andrew D.; Mounce, Andrew M.; Curry, Matthew J.; Ward, Daniel R.; Anderson, John M.; Manginell, Ronald P.; Wendt, J.R.; Rudolph, Martin R.; Pluym, Tammy P.; Lilly, Michael L.; Pioro-Ladrière, Michel; Carroll, Malcolm

Qubits based on transistor-like Si MOS nanodevices are promising for quantum computing. In this work, we demonstrate a double quantum dot spin qubit that is all-electrically controlled without the need for any external components, like micromagnets, that could complicate integration. Universal control of the qubit is achieved through spin-orbit-like and exchange interactions. Using single shot readout, we show both DC- and AC-control techniques. The fabrication technology used is completely compatible with CMOS.

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TYPE Conference Poster YEAR 2018
ScopusOSTI

Ion implantation for deterministic single atom devices

Review of Scientific Instruments

Pacheco, Jose L.; Singh, M.; Perry, Daniel L.; Wendt, J.R.; Ten Eyck, Gregory A.; Manginell, Ronald P.; Pluym, Tammy P.; Luhman, Dwight R.; Lilly, M.P.; Carroll, Malcolm; Bielejec, E.

We demonstrate a capability of deterministic doping at the single atom level using a combination of direct write focused ion beam and solid-state ion detectors. The focused ion beam system can position a single ion to within 35 nm of a targeted location and the detection system is sensitive to single low energy heavy ions. This platform can be used to deterministically fabricate single atom devices in materials where the nanostructure and ion detectors can be integrated, including donor-based qubits in Si and color centers in diamond.

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TYPE Journal Article YEAR 2017
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Tunnel coupling tuning of a QD-donor S-T qubit

Jock, Ryan M.; Jock, Ryan M.; Rudolph, Martin R.; Rudolph, Martin R.; Harvey-Collard, Patrick H.; Harvey-Collard, Patrick H.; Jacobson, Noah T.; Jacobson, Noah T.; Wendt, J.R.; Wendt, J.R.; Pluym, Tammy P.; Pluym, Tammy P.; Dominguez, Jason J.; Dominguez, Jason J.; Manginell, Ronald P.; Manginell, Ronald P.; Lilly, Michael L.; Lilly, Michael L.; Carroll, Malcolm; Carroll, Malcolm

Abstract not provided.

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TYPE Conference Poster YEAR 2017
OSTI

Coupling MOS quantum dot and phosphorous donor qubit systems

Technical Digest - International Electron Devices Meeting, IEDM

Rudolph, Martin R.; Harvey-Collard, P.; Jock, R.; Jacobson, Noah T.; Wendt, J.R.; Pluym, Tammy P.; Dominguez, Jason J.; Ten Eyck, Gregory A.; Manginell, Ronald P.; Lilly, M.P.; Carroll, Malcolm

Si-MOS based QD qubits are attractive due to their similarity to the current semiconductor industry. We introduce a highly tunable MOS foundry compatible qubit design that couples an electrostatic quantum dot (QD) with an implanted donor. We show for the first time coherent two-axis control of a two-electron spin logical qubit that evolves under the QD-donor exchange interaction and the hyperfine interaction with the donor nucleus. The two interactions are tuned electrically with surface gate voltages to provide control of both qubit axes. Qubit decoherence is influenced by charge noise, which is of similar strength as epitaxial systems like GaAs and Si/SiGe.

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TYPE Conference Poster YEAR 2017
ScopusOSTIDOI

Valley splitting of single-electron Si MOS quantum dots

Applied Physics Letters

Gamble, John K.; Harvey-Collard, Patrick; Jacobson, Noah T.; Baczewski, Andrew D.; Nielsen, Erik N.; Maurer, Leon; Montano, Ines M.; Rudolph, Martin R.; Carroll, Malcolm; Yang, C.H.; Rossi, A.; Dzurak, A.S.; Muller, Richard P.

Silicon-based metal-oxide-semiconductor quantum dots are prominent candidates for high-fidelity, manufacturable qubits. Due to silicon's band structure, additional low-energy states persist in these devices, presenting both challenges and opportunities. Although the physics governing these valley states has been the subject of intense study, quantitative agreement between experiment and theory remains elusive. Here, we present data from an experiment probing the valley states of quantum dot devices and develop a theory that is in quantitative agreement with both this and a recently reported experiment. Through sampling millions of realistic cases of interface roughness, our method provides evidence that the valley physics between the two samples is essentially the same.

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TYPE Journal Article YEAR 2016
ScopusOSTIDOI

Coupling MOS quantum dot and phosphorous donor qubit systems

IEEE International Electron Devices Meeting

Rudolph, Martin R.; Jock, Ryan M.; Jacobson, Noah T.; Wendt, J.R.; Pluym, Tammy P.; Dominguez, Jason J.; Ten Eyck, Gregory A.; Manginell, Ronald P.; Lilly, Michael L.; Carroll, Malcolm; Harvey-Collard, Patrick H.

Si-MOS based QD qubits are attractive due to their similarity to the current semiconductor industry. We introduce a highly tunable MOS foundry compatible qubit design that couples an electrostatic quantum dot (QD) with an implanted donor. We show for the first time coherent two-axis control of a two-electron spin logical qubit that evolves under the QD-donor exchange interaction and the hyperfine interaction with the donor nucleus. The two interactions are tuned electrically with surface gate voltages to provide control of both qubit axes. Qubit decoherence is influenced by charge noise, which is of similar strength as epitaxial systems like GaAs and Si/SiGe.

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TYPE Journal Article YEAR 2016
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Fabrication of quantum dots in undoped Si/Si0.8Ge0.2 heterostructures using a single metal-gate layer

Applied Physics Letters

Lu, Tzu-Ming L.; Gamble, John K.; Muller, Richard P.; Nielsen, Erik N.; Bethke, D.; Ten Eyck, Gregory A.; Pluym, Tammy P.; Wendt, J.R.; Dominguez, Jason J.; Lilly, M.P.; Carroll, Malcolm; Wanke, M.C.

Enhancement-mode Si/SiGe electron quantum dots have been pursued extensively by many groups for their potential in quantum computing. Most of the reported dot designs utilize multiple metal-gate layers and use Si/SiGe heterostructures with Ge concentration close to 30%. Here, we report the fabrication and low-temperature characterization of quantum dots in the Si/Si0.8Ge0.2 heterostructures using only one metal-gate layer. We find that the threshold voltage of a channel narrower than 1 μm increases as the width decreases. The higher threshold can be attributed to the combination of quantum confinement and disorder. We also find that the lower Ge ratio used here leads to a narrower operational gate bias range. The higher threshold combined with the limited gate bias range constrains the device design of lithographic quantum dots. We incorporate such considerations in our device design and demonstrate a quantum dot that can be tuned from a single dot to a double dot. The device uses only a single metal-gate layer, greatly simplifying device design and fabrication.

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TYPE Journal Article YEAR 2016
ScopusOSTIDOI

Single shot spin readout using a cryogenic high-electron-mobility transistor amplifier at sub-Kelvin temperatures

Applied Physics Letters

Tracy, Lisa A.; Luhman, Dwight R.; Carr, Stephen M.; Bishop, N.C.; Ten Eyck, Gregory A.; Pluym, Tammy P.; Wendt, J.R.; Lilly, M.P.; Carroll, Malcolm

We use a cryogenic high-electron-mobility transistor circuit to amplify the current from a single electron transistor, allowing for demonstration of single shot readout of an electron spin on a single P donor in Si with 100 kHz bandwidth and a signal to noise ratio of ∼9. In order to reduce the impact of cable capacitance, the amplifier is located adjacent to the Si sample, at the mixing chamber stage of a dilution refrigerator. For a current gain of ∼ 2.7 × 10 3, the power dissipation of the amplifier is 13 μW, the bandwidth is ∼ 1.3 MHz, and for frequencies above 300 kHz the current noise referred to input is ≤ 70 fA/ Hz. With this amplification scheme, we are able to observe coherent oscillations of a P donor electron spin in isotopically enriched 28Si with 96% visibility.

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TYPE Journal Article YEAR 2016
ScopusOSTIDOI

Silicon Quantum Dots with Counted Antimony Donor Implants

Sandia journal manuscript; Not yet accepted for publication

Singh, Meenakshi S.; Pacheco, Jose L.; Perry, Daniel L.; Ten Eyck, Gregory A.; Wendt, J.R.; Pluym, Tammy P.; Dominguez, Jason J.; Manginell, Ronald P.; Luhman, Dwight R.; Bielejec, Edward S.; Lilly, Michael L.; Carroll, Malcolm

Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. A focused ion beam is used to implant close to quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of ions implanted can be counted to a precision of a single ion. Regular coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization, are observed in devices with counted implants.

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TYPE Journal Article YEAR 2015
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Transport spectroscopy of low disorder silicon tunnel barriers with and without Sb implants

Nanotechnology

Shirkhorshidian, A.; Bishop, N.C.; Dominguez, Jason J.; Grubbs, R.K.; Wendt, J.R.; Lilly, M.P.; Carroll, Malcolm

We present transport measurements of silicon MOS split gate structures with and without Sb implants. We observe classical point contact (PC) behavior that is free of any pronounced unintentional resonances at liquid He temperatures. The implanted device has resonances superposed on the PC transport indicative of transport through the Sb donors. We fit the differential conductance to a rectangular tunnel barrier model with a linear barrier height dependence on source-drain voltage and non-linear dependence on gate bias. Effects such as Fowler-Nordheim (FN) tunneling and image charge barrier lowering (ICBL) are considered. Barrier heights and widths are estimated for the entire range of relevant biases. The barrier heights at the locations of some of the resonances for the implanted tunnel barrier are between 15-20 meV, which are consistent with transport through shallow partially hybridized Sb donors. The dependence of width and barrier height on gate voltage is found to be linear over a wide range of gate bias in the split gate geometry but deviates considerably when the barrier becomes large and is not described completely by standard 1D models such as FN or ICBL effects.

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TYPE Journal Article YEAR 2015
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Charge Sensed Pauli Blockade in a Metal–Oxide–Semiconductor Lateral Double Quantum Dot

Nano Letters

Nguyen, Khoi T.; Lu, Tzu-Ming L.; Muller, Richard P.; Carroll, Malcolm; Lilly, Michael L.; Nielsen, Erik N.; Bishop, Nathaniel B.; Young, Ralph W.; Wendt, J.R.; Dominguez, Jason J.; Pluym, Tammy P.; Stevens, Jeffrey S.

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.

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TYPE Journal Article YEAR 2013
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Enhancement-mode buried strained silicon channel double quantum dot with integrated electrometer

ECS Transactions

Lu, T.M.; Bishop, N.; Pluym, T.; Kotula, P.; Lilly, M.; Carroll, Malcolm

We proposed and demonstrated an enhancement-mode SiGe/strained-Si stack for a quantum dot [1], which both spaces the quantum dot away from interface defects and removes dopants. Smooth and predictable potentials for single electron quantum dots are highly desirable for beyond Moore's law approaches like quantum annealing and quantum computing. Enhancement-mode SiGe/sSi field-effect transistors (FETs) have been demonstrated previously [2,3] and have recently achieved mobilities as high as 1.6x106 cm2/V s [4], indicating that a smooth potential approaching other model systems like GaAs can be produced in Si. This material stack has subsequently been used successfully by a different group to produce coherent qubit spin rotations [5]. We report in this letter that low-disorder quantum dots can be formed using a double-top-gated lateral quantum dot nanostructure, defined using 180 nm line width platform and fabricated in a 150 mm wafer batch-processing tool set in the Sandia National Labs silicon foundry. This is an important step towards showing that defects, lithography and process tolerances in a Si foundry are sufficient to build low disorder double quantum dots for both quantum computing and quantum annealing. © The Electrochemical Society.

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TYPE Conference YEAR 2013
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Results 1–200 of 316
Results 1–200 of 316