912 research outputs found
Charge Pumping Through a Single Donor Atom
Presented in this paper is a proof-of-concept for a new approach to single
electron pumping based on a Single Atom Transistor (SAT). By charge pumping
electrons through an isolated dopant atom in silicon, precise currents of up to
160 pA at 1 GHz are generated, even if operating at 4.2 K, with no magnetic
field applied, and only when one barrier is addressed by sinusoidal voltage
cycles.Comment: 14 pages, 10 figures, few changes in the text and in figure 8, New J.
Phys. (2014) at pres
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
Dopant metrology in advanced FinFETs
Ultra-scaled FinFET transistors bear unique fingerprint-like device-to-device
differences attributed to random single impurities. This paper describes how,
through correlation of experimental data with multimillion atom tight-binding
simulations using the NEMO 3-D code, it is possible to identify the impurity's
chemical species and determine their concentration, local electric field and
depth below the Si/SiO interface. The ability to model the
excited states rather than just the ground state is the critical component of
the analysis and allows the demonstration of a new approach to atomistic
impurity metrology.Comment: 6 pages, 3 figure
Engineered valley-orbit splittings in quantum confined nanostructures in silicon
An important challenge in silicon quantum electronics in the few electron
regime is the potentially small energy gap between the ground and excited
orbital states in 3D quantum confined nanostructures due to the multiple valley
degeneracies of the conduction band present in silicon. Understanding the
"valley-orbit" (VO) gap is essential for silicon qubits, as a large VO gap
prevents leakage of the qubit states into a higher dimensional Hilbert space.
The VO gap varies considerably depending on quantum confinement, and can be
engineered by external electric fields. In this work we investigate VO
splitting experimentally and theoretically in a range of confinement regimes.
We report measurements of the VO splitting in silicon quantum dot and donor
devices through excited state transport spectroscopy. These results are
underpinned by large-scale atomistic tight-binding calculations involving over
1 million atoms to compute VO splittings as functions of electric fields, donor
depths, and surface disorder. The results provide a comprehensive picture of
the range of VO splittings that can be achieved through quantum engineering.Comment: 4 pages, 4 figure
Two path transport measurements on a triple quantum dot
We present an advanced lateral triple quantum dot made by local anodic
oxidation. Three dots are coupled in a starlike geometry with one lead attached
to each dot thus allowing for multiple path transport measurements with two
dots per path. In addition charge detection is implemented using a quantum
point contact. Both in charge measurements as well as in transport we observe
clear signatures of states from each dot. Resonances of two dots can be
established allowing for serial transport via the corresponding path. Quadruple
points with all three dots in resonance are prepared for different electron
numbers and analyzed concerning the interplay of the simultaneously measured
transport along both paths.Comment: 4 pages, 4 figure
Thermodynamic insight into stimuli-responsive behaviour of soft porous crystals
Knowledge of the thermodynamic potential in terms of the independent variables allows to characterize the macroscopic state of the system. However, in practice, it is difficult to access this potential experimentally due to irreversible transitions that occur between equilibrium states. A showcase example of sudden transitions between (meta) stable equilibrium states is observed for soft porous crystals possessing a network with long-range structural order, which can transform between various states upon external stimuli such as pressure, temperature and guest adsorption. Such phase transformations are typically characterized by large volume changes and may be followed experimentally by monitoring the volume change in terms of certain external triggers. Herein, we present a generalized thermodynamic approach to construct the underlying Helmholtz free energy as a function of the state variables that governs the observed behaviour based on microscopic simulations. This concept allows a unique identification of the conditions under which a material becomes flexible
Lifetime enhanced transport in silicon due to spin and valley blockade
We report the observation of Lifetime Enhanced Transport (LET) based on
perpendicular valleys in silicon by transport spectroscopy measurements of a
two-electron system in a silicon transistor. The LET is manifested as a
peculiar current step in the stability diagram due to a forbidden transition
between an excited state and any of the lower energy states due perpendicular
valley (and spin) configurations, offering an additional current path. By
employing a detailed temperature dependence study in combination with a rate
equation model, we estimate the lifetime of this particular state to exceed 48
ns. The two-electron spin-valley configurations of all relevant confined
quantum states in our device were obtained by a large-scale atomistic
tight-binding simulation. The LET acts as a signature of the complicated valley
physics in silicon; a feature that becomes increasingly important in silicon
quantum devices.Comment: 4 pages, 4 figures. (The current version (v3) is the result of
splitting up the previous version (v2), and has been completely rewritten
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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