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Photothermal alternative to device fabrication using atomic precision advanced manufacturing techniques

Proceedings of SPIE - The International Society for Optical Engineering

Katzenmeyer, Aaron M.; Dmitrovic, S.; Baczewski, Andrew D.; Bussmann, Ezra B.; Lu, Tzu-Ming L.; Anderson, Evan M.; Schmucker, S.W.; Ivie, J.A.; Campbell, DeAnna M.; Ward, D.R.; Wang, George T.; Misra, Shashank M.

The attachment of dopant precursor molecules to depassivated areas of hydrogen-terminated silicon templated with a scanning tunneling microscope (STM) has been used to create electronic devices with sub-nanometer precision, typically for quantum physics demonstrations, and to dope silicon past the solid-solubility limit, with potential applications in microelectronics and plasmonics. However, this process, which we call atomic precision advanced manufacturing (APAM), currently lacks the throughput required to develop sophisticated applications because there is no proven scalable hydrogen lithography pathway. Here, we demonstrate and characterize an APAM device workflow where STM lithography has been replaced with photolithography. An ultraviolet laser is shown to locally heat silicon controllably above the temperature required for hydrogen depassivation. STM images indicate a narrow range of laser energy density where hydrogen has been depassivated, and the surface remains well-ordered. A model for photothermal heating of silicon predicts a local temperature which is consistent with atomic-scale STM images of the photo-patterned regions. Finally, a simple device made by exposing photo-depassivated silicon to phosphine is found to have a carrier density and mobility similar to that produced by similar devices patterned by STM.

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TYPE Journal Article YEAR 2020
ScopusOSTIDOI

Designer quantum materials

Misra, Shashank M.; Ward, Daniel R.; Baczewski, Andrew D.; Campbell, Quinn C.; Schmucker, Scott W.; Mounce, Andrew M.; Tracy, Lisa A.; Lu, Tzu-Ming L.; Marshall, Michael T.; Campbell, DeAnna M.

Quantum materials have long promised to revolutionize everything from energy transmission (high temperature superconductors) to both quantum and classical information systems (topological materials). However, their discovery and application has proceeded in an Edisonian fashion due to both an incomplete theoretical understanding and the difficulty of growing and purifying new materials. This project leverages Sandia's unique atomic precision advanced manufacturing (APAM) capability to design small-scale tunable arrays (designer materials) made of donors in silicon. Their low-energy electronic behavior can mimic quantum materials, and can be tuned by changing the fabrication parameters for the array, thereby enabling the discovery of materials systems which can't yet be synthesized. In this report, we detail three key advances we have made towards development of designer quantum materials. First are advances both in APAM technique and underlying mechanisms required to realize high-yielding donor arrays. Second is the first-ever observation of distinct phases in this material system, manifest in disordered 2D sheets of donors. Finally are advances in modeling the electronic structure of donor clusters and regular structures incorporating them, critical to understanding whether an array is expected to show interesting physics. Combined, these establish the baseline knowledge required to manifest the strongly-correlated phases of the Mott-Hubbard model in donor arrays, the first step to deploying APAM donor arrays as analogues of quantum materials.

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TYPE SAND Report YEAR 2019
OSTIDOI

Gate-defined quantum dots in Ge/SiGe quantum wells as a platform for spin qubits

ECS Transactions

Hardy, Will H.; Su, Y.H.; Chuang, Y.; Maurer, L.N.; Brickson, M.; Baczewski, Andrew D.; Li, J.Y.; Lu, Tzu-Ming L.; Luhman, Dwight R.

In the field of semiconductor quantum dot spin qubits, there is growing interest in leveraging the unique properties of hole-carrier systems and their intrinsically strong spin-orbit coupling to engineer novel qubits. Recent advances in semiconductor heterostructure growth have made available high quality, undoped Ge/SiGe quantum wells, consisting of a pure strained Ge layer flanked by Ge-rich SiGe layers above and below. These quantum wells feature heavy hole carriers and a cubic Rashba-type spin-orbit interaction. Here, we describe progress toward realizing spin qubits in this platform, including development of multi-metal-layer gated device architectures, device tuning protocols, and charge-sensing capabilities. Iterative improvement of a three-layer metal gate architecture has significantly enhanced device performance over that achieved using an earlier single-layer gate design. We discuss ongoing, simulation-informed work to fine-tune the device geometry, as well as efforts toward a single-spin qubit demonstration.

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TYPE Conference Poster YEAR 2019
ScopusOSTIDOI

Weak anti-localization of two-dimensional holes in germanium beyond the diffusive regime

Nanoscale

Chou, C.T.; Jacobson, Noah T.; Moussa, J.E.; Baczewski, Andrew D.; Chuang, Y.; Liu, C.Y.; Li, J.Y.; Lu, Tzu-Ming L.

Gate-controllable spin-orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin-orbit precession time, spin-orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin-orbit coupling. As the density becomes larger than ∼6 × 1011 cm-2, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.

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TYPE Journal Article YEAR 2018
ScopusOSTIDOI
Results 51–100 of 178
Results 51–100 of 178