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Search Results: 1 - 10 of 2144 matches for " Sven Rogge "
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Local Kondo temperatures in atomic chains
Ricardo Agundez,Joe Salfi,Sven Rogge,Miriam Blaauboer
Physics , 2014, DOI: 10.1103/PhysRevB.91.041117
Abstract: We study the effect of disorder in strongly interacting small atomic chains. Using the Kotliar- Ruckenstein slave-boson approach we diagonalize the Hamiltonian via scattering matrix theory. We numerically solve the Kondo transmission and the slave-boson parameters that allow us to calculate the Kondo temperature. We demonstrate that in the weak disorder regime, disorder in the energy levels of the dopants induces a non-screened disorder in the Kondo couplings of the atoms. We show that disorder increases the Kondo temperature of a perfect chain. We find that this disorder in the couplings comes from a local distribution of Kondo temperatures along the chain. We propose two experimental setups where the impact of local Kondo temperatures can be observed.
Gate induced g-factor control and dimensional transition for donors in multi-valley semiconductors
Rajib Rahman,Seung H. Park,Timothy B. Boykin,Gerhard Klimeck,Sven Rogge,Lloyd C. L. Hollenberg
Physics , 2009, DOI: 10.1103/PhysRevB.80.155301
Abstract: The dependence of the g-factors of semiconductor donors on applied electric and magnetic fields is of immense importance in spin based quantum computation and in semiconductor spintronics. The donor g-factor Stark shift is sensitive to the orientation of the electric and magnetic fields and strongly influenced by the band-structure and spin-orbit interactions of the host. Using a multimillion atom tight-binding framework the spin-orbit Stark parameters are computed for donors in multi-valley semiconductors, silicon and germanium. Comparison with limited experimental data shows good agreement for a donor in silicon. Results for gate induced transition from 3D to 2D wave function confinement show that the corresponding g-factor shift in Si is experimentally observable.
Coherent frequency up-conversion of microwaves to the optical telecommunications band in an Er:YSO crystal
Xavier Fernandez-Gonzalvo,Yu-Hui Chen,Chunming Yin,Sven Rogge,Jevon J. Longdell
Physics , 2015,
Abstract: The ability to convert quantum states from microwave photons to optical photons is important for hybrid system approaches to quantum information processing. In this paper we report the up-conversion of a microwave signal into the optical telecommunications wavelength band using erbium dopants in a yttrium orthosilicate crystal via stimulated Raman scattering. The microwaves were applied to the sample using a 3D copper loop-gap resonator and the coupling and signal optical fields were single passed. The conversion efficiency was low, in agreement with a theoretical analysis, but can be significantly enhanced with an optical resonator.
Bulk and sub-surface donor bound excitons in silicon under electric fields
Rajib Rahman,Jan Verduijn,Yu Wang,Chunming Yin,Gabriele De Boo,Gerhard Klimeck,Sven Rogge
Physics , 2015,
Abstract: The electronic structure of the three-particle donor bound exciton (D$^0$X) in silicon is computed using a large-scale atomic orbital tight-binding method within the Hartree approximation. The calculations yield a transition energy close to the experimentally measured value of 1150 meV in bulk, and show how the transition energy and transition probability can change with applied fields and proximity to surfaces, mimicking the conditions of realistic devices. The spin-resolved transition energy from a neutral donor state (D$^0$) to D$^0$X depends on the three-particle Coulomb energy, and the interface and electric field induced hyperfine splitting and heavy-hole-light-hole splitting. Although the Coulomb energy decreases as a result of Stark shift, the spatial separation of the electron and hole wavefunctions by the field also reduces the transition dipole. A bulk-like D$^0$X dissociates abruptly at a modest electric field, while a D$^0$X at a donor close to an interface undergoes a gradual ionization process. Our calculations take into account the full bandstructure of silicon and the full energy spectrum of the donor including spin directly in the atomic orbital basis and treat the three-particle Coulomb interaction self-consistently to provide quantitative guidance to experiments aiming to realize hybrid opto-electric techniques for addressing donor qubits.
Thermionic Emission as a tool to study transport in undoped nFinFETs
Giuseppe C. Tettamanzi,Abhijeet Paul,Gabriel P. Lansbergen,Jan Verduijn,Sunhee Lee,Nadine Collaert,Serge Biesemans,Gerhard Klimeck,Sven Rogge
Physics , 2010, DOI: 10.1109/LED.2009.2036134
Abstract: Thermally activated sub-threshold transport has been investigated in undoped triple gate MOSFETs. The evolution of the barrier height and of the active cross-section area of the channel as a function of gate voltage has been determined. The results of our experiments and of the Tight Binding simulations we have developed are both in good agreement with previous analytical calculations, confirming the validity of thermionic approach to investigate transport in FETs. This method provides an important tool for the improvement of devices characteristics.
Interface trap density metrology from sub-threshold transport in highly scaled undoped Si n-FinFETs
Abhijeet Paul,Giuseppe C. Tettamanzi,Sunhee Lee,Saumitra Mehrotra,Nadine Colleart,Serge Biesemans,Sven Rogge,Gerhard Klimeck
Physics , 2011, DOI: 10.1063/1.3660697
Abstract: Channel conductance measurements can be used as a tool to study thermally activated electron transport in the sub-threshold region of state-of-art FinFETs. Together with theoretical Tight-Binding (TB) calculations, this technique can be used to understand the evolution of source-to-channel barrier height (Eb) and of active channel area (S) with gate bias (Vgs). The quantitative difference between experimental and theoretical values that we observe can be attributed to the interface traps present in these FinFETs. Therefore, based on the difference between measured and calculated values of (i) S and (ii) |dEb/dVgs| (channel to gate coupling), two new methods of interface trap density (Dit) metrology are outlined. These two methods are shown to be very consistent and reliable, thereby opening new ways of analyzing in situ state-of-the-art multi-gate FETs down to the few nm width limit. Furthermore, theoretical investigation of the spatial current density reveal volume inversion in thinner FinFETs near the threshold voltage.
Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory
Muhammad Usman,Rajib Rahman,Joe Salfi,Juanita Bocquel,Benoit Voisin,Sven Rogge,Gerhard Klimeck,Lloyd L. C. Hollenberg
Physics , 2014, DOI: 10.1088/0953-8984/27/15/154207
Abstract: Atomistic tight-binding (TB) simulations are performed to calculate the Stark shift of the hyperfine coupling for a single Arsenic (As) donor in Silicon (Si). The role of the central-cell correction is studied by implementing both the static and the non-static dielectric screenings of the donor potential, and by including the effect of the lattice strain close to the donor site. The dielectric screening of the donor potential tunes the value of the quadratic Stark shift parameter ($\eta_2$) from -1.3 $\times$ 10$^{-3} \mu$m$^2$/V$^2$ for the static dielectric screening to -1.72 $\times$ 10$^{-3} \mu$m$^2$/V$^2$ for the non-static dielectric screening. The effect of lattice strain, implemented by a 3.2% change in the As-Si nearest-neighbour bond length, further shifts the value of $\eta_2$ to -1.87 $\times$ 10$^{-3} \mu$m$^2$/V$^2$, resulting in an excellent agreement of theory with the experimentally measured value of -1.9 $\pm$ 0.2 $\times$ 10$^{-3} \mu$m$^2$/V$^2$. Based on our direct comparison of the calculations with the experiment, we conclude that the previously ignored non-static dielectric screening of the donor potential and the lattice strain significantly influence the donor wave function charge density and thereby leads to a better agreement with the available experimental data sets.
Strain and Electric Field Control of Hyperfine Interactions for Donor Spin Qubits in Silicon
Muhammad Usman,Charles D. Hill,Rajib Rahman,Gerhard Klimeck,Michelle Y. Simmons,Sven Rogge,Lloyd C. L. Hollenberg
Physics , 2015, DOI: 10.1103/PhysRevB.91.245209
Abstract: Control of hyperfine interactions is a fundamental requirement for quantum computing architecture schemes based on shallow donors in silicon. However, at present, there is lacking an atomistic approach including critical effects of central-cell corrections and non-static screening of the donor potential capable of describing the hyperfine interaction in the presence of both strain and electric fields in realistically sized devices. We establish and apply a theoretical framework, based on atomistic tight-binding theory, to quantitatively determine the strain and electric field dependent hyperfine couplings of donors. Our method is scalable to millions of atoms, and yet captures the strain effects with an accuracy level of DFT method. Excellent agreement with the available experimental data sets allow reliable investigation of the design space of multi-qubit architectures, based on both strain-only as well as hybrid (strain+field) control of qubits. The benefits of strain are uncovered by demonstrating that a hybrid control of qubits based on (001) compressive strain and in-plane (100 or 010) fields results in higher gate fidelities and/or faster gate operations, for all of the four donor species considered (P, As, Sb, and Bi). The comparison between different donor species in strained environments further highlights the trends of hyperfine shifts, providing predictions where no experimental data exists. Whilst faster gate operations are realisable with in-plane fields for P, As, and Sb donors, only for the Bi donor, our calculations predict faster gate response in the presence of both in-plane and out-of-plane fields, truly benefiting from the proposed planar field control mechanism of the hyperfine interactions.
A planar Al-Si Schottky Barrier MOSFET operated at cryogenic temperatures
Wendy E. Purches,Alessandro Rossi,Ruichen Zhao,Sergey Kafanov,Timothy L. Duty,Andrew S. Dzurak,Sven Rogge,Giuseppe C. Tettamanzi
Physics , 2015, DOI: 10.1063/1.4928589
Abstract: Schottky Barrier (SB)-MOSFET technology offers intriguing possibilities for cryogenic nano-scale devices, such as Si quantum devices and superconducting devices. We present experimental results on a novel device architecture where the gate electrode is self-aligned with the device channel and overlaps the source and drain electrodes. This facilitates a sub-5 nm gap between the source/drain and channel, and no spacers are required. At cryogenic temperatures, such devices function as p-MOS Tunnel FETs, as determined by the Schottky barrier at the Al-Si interface, and as a further advantage, fabrication processes are compatible with both CMOS and superconducting logic technology.
Interface Trap Density Metrology of state-of-the-art undoped Si n-FinFETs
Giuseppe Carlo Tettamanzi,Abhijeet Paul,Sunhee Lee,Saumitra R. Mehrotra,Nadine Collaert,Serge Biesemans,Gerhard Klimeck,Sven Rogge
Physics , 2010,
Abstract: The presence of interface states at the MOS interface is a well-known cause of device degradation. This is particularly true for ultra-scaled FinFET geometries where the presence of a few traps can strongly influence device behavior. Typical methods for interface trap density (Dit) measurements are not performed on ultimate devices, but on custom designed structures. We present the first set of methods that allow direct estimation of Dit in state-of-the-art FinFETs, addressing a critical industry need.
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