37 research outputs found
Measurement of phosphorus segregation in silicon at the atomic-scale using STM
In order to fabricate precise atomic-scale devices in silicon using a
combination of scanning tunnelling microscopy (STM) and molecular beam epitaxy
it is necessary to minimize the segregation/diffusion of dopant atoms during
silicon encapsulation. We characterize the surface segregation/diffusion of
phosphorus atoms from a -doped layer in silicon after encapsulation at
250C and room temperature using secondary ion mass spectrometry
(SIMS), Auger electron spectroscopy (AES), and STM. We show that the surface
phosphorus density can be reduced to a few percent of the initial
-doped density if the phosphorus atoms are encapsulated with 5 or 10
monolayers of epitaxial silicon at room temperature. We highlight the
limitations of SIMS and AES to determine phosphorus segregation at the
atomic-scale and the advantage of using STM directly
Exact location of dopants below the Si(001):H surface from scanning tunnelling microscopy and density functional theory
Control of dopants in silicon remains the most important approach to
tailoring the properties of electronic materials for integrated circuits, with
Group V impurities the most important n-type dopants. At the same time, silicon
is finding new applications in coherent quantum devices, thanks to the
magnetically quiet environment it provides for the impurity orbitals. The
ionization energies and the shape of the dopant orbitals depend on the surfaces
and interfaces with which they interact. The location of the dopant and local
environment effects will therefore determine the functionality of both future
quantum information processors and next-generation semiconductor devices. Here
we match observed dopant wavefunctions from low-temperature scanning tunnelling
microscopy (STM) to images simulated from first-principles density functional
theory (DFT) calculations. By this combination of experiment and theory we
precisely determine the substitutional sites of neutral As dopants between 5
and 15A below the Si(001):H surface. In the process we gain a full
understanding of the interaction of the donor-electron state with the surface,
and hence of the transition between the bulk dopant (with its delocalised
hydrogenic orbital) and the previously studied dopants in the surface layer.Comment: 12 pages; accepted for publication in Phys. Rev.
Topological phases of a dimerized Fermi-Hubbard model for semiconductor nano-lattices
Motivated by recent advances in fabricating artificial lattices in
semiconductors and their promise for quantum simulation of topological
materials, we study the one-dimensional dimerized Fermi-Hubbard model. We show
how the topological phases at half-filling can be characterized by a reduced
Zak phase defined based on the reduced density matrix of each spin subsystem.
Signatures of bulk-boundary correspondence are observed in the triplon
excitation of the bulk and the edge states of uncoupled spins at the
boundaries. At quarter-filling we show that owing to the presence of the
Hubbard interaction the system can undergo a transition to the topological
ground state of the non-interacting Su-Schrieffer-Heeger model with the
application of a moderate-strength external magnetic field. We propose a robust
experimental realization with a chain of dopant atoms in silicon or
gate-defined quantum dots in GaAs where the transition can be probed by
measuring the tunneling current through the many-body state of the chain.Comment: 11 pages, 7 figure
Bismuth trichloride as a molecular precursor for silicon doping
Dopant impurity species can be incorporated into the silicon (001) surface via the adsorption and dissociation of simple precursor molecules. Examples include phosphine (PH3), arsine (AsH3), and diborane (B2H6) for the incorporation of phosphorus, arsenic, and boron, respectively. Through exploitation of precursor surface chemistry, the spatial locations of these incorporated dopants can be controlled at the atomic scale via the patterning of a hydrogen lithographic resist layer using scanning tunneling microscopy (STM). There is strong interest in the spatial control of bismuth atoms incorporated into silicon for quantum technological applications; however, there is currently no known precursor for the incorporation of bismuth that is compatible with this STM-based lithographic method. Here, we explore the precursor chemistry (adsorption, diffusion, and dissociation) of bismuth trichloride (BiCl3) on Si(001). We show atomic-resolution STM images of BiCl3 exposed Si(001) surfaces at low coverage and combine this with density functional theory calculations to produce a model of the surface processes and the observed features. Our results show that, at room temperature, BiCl3 completely dissociates to produce bismuth ad-atoms, ad-dimers, and surface-bound chlorine, and we explain how BiCl3 is a strong candidate for a bismuth precursor compound compatible with lithographic patterning at the sub-nanometer scale
Spatially resolved dielectric loss at the Si/SiO interface
The Si/SiO interface is populated by isolated trap states which modify
its electronic properties. These traps are of critical interest for the
development of semiconductor-based quantum sensors and computers, as well as
nanoelectronic devices. Here, we study the electric susceptibility of the
Si/SiO interface with nm spatial resolution using frequency-modulated
atomic force microscopy to measure a patterned dopant delta-layer buried 2 nm
beneath the silicon native oxide interface. We show that surface charge
organization timescales, which range from 1-150 ns, increase significantly
around interfacial states. We conclude that dielectric loss under time-varying
gate biases at MHz and sub-MHz frequencies in metal-insulator-semiconductor
capacitor device architectures is highly spatially heterogeneous over nm length
scales
Room Temperature Incorporation of Arsenic Atoms into the Germanium (001) Surface**
Germanium has emerged as an exceptionally promising material for spintronics and quantum information applications, with significant fundamental advantages over silicon. However, efforts to create atomic-scale devices using donor atoms as qubits have largely focused on phosphorus in silicon. Positioning phosphorus in silicon with atomic-scale precision requires a thermal incorporation anneal, but the low success rate for this step has been shown to be a fundamental limitation prohibiting the scale-up to large-scale devices. Here, we present a comprehensive study of arsine (AsH3) on the germanium (001) surface. We show that, unlike any previously studied dopant precursor on silicon or germanium, arsenic atoms fully incorporate into substitutional surface lattice sites at room temperature. Our results pave the way for the next generation of atomic-scale donor devices combining the superior electronic properties of germanium with the enhanced properties of arsine/germanium chemistry that promises scale-up to large numbers of deterministically placed qubits
Room Temperature Incorporation of Arsenic Atoms into the Germanium (001) Surface
Germanium has emerged as an exceptionally promising material for spintronics and quantum information applications, with significant fundamental advantages over silicon. However, efforts to create atomic-scale devices using donor atoms as qubits have largely focused on phosphorus in silicon. Positioning phosphorus in silicon with atomic-scale precision requires a thermal incorporation anneal, but the low success rate for this step has been shown to be a fundamental limitation prohibiting the scale-up to large-scale devices. Here, we present a comprehensive study of arsine (AsH3) on the germanium (001) surface. We show that, unlike any previously studied dopant precursor on silicon or germanium, arsenic atoms fully incorporate into substitutional surface lattice sites at room temperature. Our results pave the way for the next generation of atomic-scale donor devices combining the superior electronic properties of germanium with the enhanced properties of arsine/germanium chemistry that promises scale-up to large numbers of deterministically placed qubits
Single-Atom Control of Arsenic Incorporation in Silicon for High-Yield Artificial Lattice Fabrication
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. In this
work, we report precise and repeatable, substitutional incorporation of single
arsenic atoms into a silicon lattice. We employ a combination of scanning
tunnelling microscopy hydrogen resist lithography and a detailed statistical
exploration of the chemistry of arsine on the hydrogen terminated silicon (001)
surface, to show that single arsenic dopants can be deterministically placed
within four silicon lattice sites and incorporated with 972% yield. These
findings bring us closer to the ultimate frontier in semiconductor technology:
the deterministic assembly of atomically precise dopant and qubit arrays at
arbitrarily large scales
Microwave Properties of 2D CMOS Compatible Co-Planar Waveguides Made from Phosphorus Dopant Monolayers in Silicon
Low-dimensional microwave interconnects have important applications for nanoscale electronics, from complementary metal–oxide-semiconductor (CMOS) to silicon quantum technologies. Graphene is naturally nanoscale and has already demonstrated attractive electronic properties, however its application to electronics is limited by available fabrication techniques and CMOS incompatibility. Here, the characteristics of transmission lines made from silicon doped with phosphorus are investigated using phosphine monolayer doping. S-parameter measurements are performed between 4–26 GHz from room temperature down to 4.5 K. At 20 GHz, the measured monolayer transmission line characteristics consist of an attenuation constant of 40 dB mm−1 and a characteristic impedance of 600 Ω. The results indicate that Si:P monolayers are a viable candidate for microwave transmission and that they have a.c. properties similar to graphene, with the additional benefit of extremely precise, reliable, stable, and inherently CMOS compatible fabrication