743 research outputs found
Enhanced tunneling across nanometer-scale metal-semiconductor interfaces
We have measured electrical transport across epitaxial, nanometer-sized
metal-semiconductor interfaces by contacting CoSi2-islands grown on Si(111)
with an STM-tip. The conductance per unit area was found to increase with
decreasing diode area. Indeed, the zero-bias conductance was found to be about
10^4 times larger than expected from downscaling a conventional diode. These
observations are explained by a model, which predicts a narrower barrier for
small diodes and therefore a greatly increased contribution of tunneling to the
electrical transport.Comment: 3 pages, 2 EPS-figures; accepted for publication in Appl. Phys. Let
Scaling of nano-Schottky-diodes
A generally applicable model is presented to describe the potential barrier
shape in ultra small Schottky diodes. It is shown that for diodes smaller than
a characteristic length (associated with the semiconductor doping level)
the conventional description no longer holds. For such small diodes the
Schottky barrier thickness decreases with decreasing diode size. As a
consequence, the resistance of the diode is strongly reduced, due to enhanced
tunneling. Without the necessity of assuming a reduced (non-bulk) Schottky
barrier height, this effect provides an explanation for several experimental
observations of enhanced conduction in small Schottky diodes.Comment: 4 pages, 4 figures, accepted for publication in Appl. Phys. Lett.,
some minor additions and correction
Towards visualisation of central-cell-effects in scanning-tunnelling-microscope images of subsurface dopant qubits in silicon
Atomic-scale understanding of phosphorous donor wave functions underpins the
design and optimisation of silicon based quantum devices. The accuracy of
large-scale theoretical methods to compute donor wave functions is dependent on
descriptions of central-cell-corrections, which are empirically fitted to match
experimental binding energies, or other quantities associated with the global
properties of the wave function. Direct approaches to understanding such
effects in donor wave functions are of great interest. Here, we apply a
comprehensive atomistic theoretical framework to compute scanning tunnelling
microscopy (STM) images of subsurface donor wave functions with two
central-cell-correction formalisms previously employed in the literature. The
comparison between central-cell models based on real-space image features and
the Fourier transform profiles indicate that the central-cell effects are
visible in the simulated STM images up to ten monolayers below the silicon
surface. Our study motivates a future experimental investigation of the
central-cell effects via STM imaging technique with potential of fine tuning
theoretical models, which could play a vital role in the design of donor-based
quantum systems in scalable quantum computer architectures.Comment: Nanoscale 201
Balanced ternary addition using a gated silicon nanowire
We demonstrate the proof of principle for a ternary adder using silicon
metal-on-insulator single electron transistors (SET). Gate dependent rectifying
behavior of a single electron transistor results in a robust three-valued
output as a function of the potential of the SET island. Mapping logical,
ternary inputs to the three gates controlling the potential of the SET island
allows us to perform complex, inherently ternary operations, on a single
transistor
Magnetic Field Probing of an SU(4) Kondo Resonance in a Single Atom Transistor
Semiconductor nano-devices have been scaled to the level that transport can
be dominated by a single dopant atom. In the strong coupling case a Kondo
effect is observed when one electron is bound to the atom. Here, we report on
the spin as well as orbital Kondo ground state. We experimentally as well than
theoretically show how we can tune a symmetry transition from a SU(4) ground
state, a many body state that forms a spin as well as orbital singlet by
virtual exchange with the leads, to a pure SU(2) orbital ground state, as a
function of magnetic field. The small size and the s-like orbital symmetry of
the ground state of the dopant, make it a model system in which the magnetic
field only couples to the spin degree of freedom and allows for observation of
this SU(4) to SU(2) transition.Comment: 12 pages, 10 figures, accepted for publication in Physical Review
Letter
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