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Search Results: 1 - 10 of 351270 matches for " G. P. Lansbergen "
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Coherent transport through a double donor system in silicon
J. Verduijn,G. C. Tettamanzi,G. P. Lansbergen,N. Collaert,S. Biesemans,S. Rogge
Physics , 2009, DOI: 10.1063/1.3318271
Abstract: Quantum coherence is of crucial importance for the applicability of donor based quantum computing. In this Letter we describe the observation of the interference of conduction paths induced by two donors in a nano-MOSFET resulting in a Fano resonance. This demonstrates the coherent exchange of electrons between two donors. In addition, the phase difference between the two conduction paths can be tuned by means of a magnetic field, in full analogy to the Aharonov-Bohm effect.
Heterointerface effects on the charging energy of shallow D- ground state in silicon: the role of dielectric mismatch
M. J. Calderon,J. Verduijn,G. P. Lansbergen,G. C. Tettamanzi,S. Rogge,Belita Koiller
Physics , 2010, DOI: 10.1103/PhysRevB.82.075317
Abstract: Donor states in Si nanodevices can be strongly modified by nearby insulating barriers and metallic gates. We report here experimental results indicating a strong reduction in the charging energy of isolated As dopants in Si FinFETs relative to the bulk value. By studying the problem of two electrons bound to a shallow donor within the effective mass approach, we find that the measured small charging energy may be due to a combined effect of the insulator screening and the proximity of metallic gates.
Tunable Kondo effect in a single donor atom
G. P. Lansbergen,G. C. Tettamanzi,J. Verduijn,N. Collaert,S. Biesemans,M. Blaauboer,S. Rogge
Physics , 2009, DOI: 10.1021/nl9031132
Abstract: The Kondo effect has been observed in a single gate-tunable atom. The measurement device consists of a single As dopant incorporated in a Silicon nanostructure. The atomic orbitals of the dopant are tunable by the gate electric field. When they are tuned such that the ground state of the atomic system becomes a (nearly) degenerate superposition of two of the Silicon valleys, an exotic and hitherto unobserved valley Kondo effect appears. Together with the regular spin Kondo, the tunable valley Kondo effect allows for reversible electrical control over the symmetry of the Kondo ground state from an SU(2)- to an SU(4) -configuration.
Dopant metrology in advanced FinFETs
G. P. Lansbergen,R. Rahman,G. C. Tettamanzi,J. Verduijn,L. C. L. Hollenberg,G. Klimeck,S. Rogge
Physics , 2011,
Abstract: 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$_{\mathrm{2}}$ 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.
Magnetic Field Probing of an SU(4) Kondo Resonance in a Single Atom Transistor
G. C. Tettamanzi,J. Verduijn,G. P. Lansbergen,M. Blaauboer,M. J. Calderón,R. Aguado,S. Rogge
Physics , 2011, DOI: 10.1103/PhysRevLett.108.046803
Abstract: 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.
Engineered valley-orbit splittings in quantum confined nanostructures in silicon
R. Rahman,J. Verduijn,N. Kharche,G. P. Lansbergen,G. Klimeck,L. C. L. Hollenberg,S. Rogge
Physics , 2011, DOI: 10.1103/PhysRevB.83.195323
Abstract: 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.
Orbital Stark effect and quantum confinement transition of donors in silicon
Rajib Rahman,G. P. Lansbergen,Seung H. Park,J. Verduijn,Gerhard Klimeck,S. Rogge,Lloyd C. L. Hollenberg
Physics , 2009, DOI: 10.1103/PhysRevB.80.165314
Abstract: Adiabatic shuttling of single impurity bound electrons to gate induced surface states in semiconductors has attracted much attention in recent times, mostly in the context of solid-state quantum computer architecture. A recent transport spectroscopy experiment for the first time was able to probe the Stark shifted spectrum of a single donor in silicon buried close to a gate. Here we present the full theoretical model involving large-scale quantum mechanical simulations that was used to compute the Stark shifted donor states in order to interpret the experimental data. Use of atomistic tight-binding technique on a domain of over a million atoms helped not only to incorporate the full band structure of the host, but also to treat realistic device geometries and donor models, and to use a large enough basis set to capture any number of donor states. The method yields a quantitative description of the symmetry transition that the donor electron undergoes from a 3D Coulomb confined state to a 2D surface state as the electric field is ramped up adiabatically. In the intermediate field regime, the electron resides in a superposition between the states of the atomic donor potential and that of the quantum dot like states at the surface. In addition to determining the effect of field and donor depth on the electronic structure, the model also provides a basis to distinguish between a phosphorus and an arsenic donor based on their Stark signature. The method also captures valley-orbit splitting in both the donor well and the interface well, a quantity critical to silicon qubits. The work concludes with a detailed analysis of the effects of screening on the donor spectrum.
Transport spectroscopy of a single dopant in a gated silicon nanowire
H. Sellier,G. P. Lansbergen,J. Caro,N. Collaert,I. Ferain,M. Jurczak,S. Biesemans,S. Rogge
Physics , 2006, DOI: 10.1103/PhysRevLett.97.206805
Abstract: We report on spectroscopy of a single dopant atom in silicon by resonant tunneling between source and drain of a gated nanowire etched from silicon on insulator. The electronic states of this dopant isolated in the channel appear as resonances in the low temperature conductance at energies below the conduction band edge. We observe the two possible charge states successively occupied by spin-up and spin-down electrons under magnetic field. The first resonance is consistent with the binding energy of the neutral $D^0$ state of an arsenic donor. The second resonance shows a reduced charging energy due to the electrostatic coupling of the charged $D^-$ state with electrodes. Excited states and Zeeman splitting under magnetic field present large energies potentially useful to build atomic scale devices.
Sub-threshold channels at the edges of nanoscale triple-gate silicon transistors
H. Sellier,G. P. Lansbergen,J. Caro,N. Collaert,I. Ferain,M. Jurczak,S. Biesemans,S. Rogge
Physics , 2006, DOI: 10.1063/1.2476343
Abstract: We investigate by low-temperature transport experiments the sub-threshold behavior of triple-gate silicon field-effect transistors. These three-dimensional nano-scale devices consist of a lithographically defined silicon nanowire surrounded by a gate with an active region as small as a few tens of nanometers, down to 50x60x35 nm^3. Conductance versus gate voltage show Coulomb-blockade oscillations with a large charging energy due to the formation of a small potential well below the gate. According to dependencies on device geometry and thermionic current analysis, we conclude that sub-threshold channels, a few nanometers wide, appear at the nanowire edges, hence providing an experimental evidence for the corner-effect.
Lifetime enhanced transport in silicon due to spin and valley blockade
G. P. Lansbergen,R. Rahman,J. Verduijn,G. C. Tettamanzi,N. Collaert,S. Biesemans,G. Klimeck,L. C. L. Hollenberg,S. Rogge
Physics , 2010, DOI: 10.1103/PhysRevLett.107.136602
Abstract: 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.
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