All pulications (111)

• 81:

  Title: Verduijn J; Tettamanzi GC; Roggea S, 2013, 'Orbital structure and transport characteristics of single donors', in Prati E; Shinada T (ed.), Single-Atom Nanoelectronics, Pan Stanford Publishing, Stanford, pp. 211 - 230
     

  Year : 2013

  Publication Type: Book Chapters

  Topic: 2D Materials

  Abstract

  Single-Atom Nanoelectronics covers the fabrication of single-atom devices and related technology, as well as the relevant electronic equipment and the intriguing new phenomena related to single-atom and single-electron effects in quantum devices. It also covers the alternative approaches related to both silicon- and carbon-based technologies, also from the point of view of large-scale industrial production. The publication provides a comprehensive picture of the state of the art at the cutting edge and constitutes a milestone in the emerging field of beyond-CMOS technology.Although there are numerous publications on nanoelectronics, no book highlights the effect of a single atom on device performance, which can be beneficial for making extensive use of CMOS technologies. This book is the first to deal with topics related to single-atom control, which is the final frontier for nanoelectronics.

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• 82:

  Title: Tettamanzi G, 2012, 'Dopant Metrology in Advanced FinFETs', in Collaert N (ed.), CMOS NANOELECTRONICS: INNOVATIVE DEVICES, ARCHITECTURES, AND APPLICATIONS, Pan Stanford Publishing 2012, Singapore, pp. 399 - 412
     

  Year : 2012

  Publication Type: Book Chapters

  Topic:

  Abstract

  Ultra-scaled FinFET transistors bear unique fingerprint-like device-to-device differences attributed to random single impurities. Thischapter describes how, through correlation of experimental datawith multimillion atom tight-binding simulations using the NEMO3-D code, it is possible to identify the impurity’s chemical speciesand determine their concentration, local electric field and depthbelow the Si/SiO2 interface. The ability to model the excited statesrather than just the ground state is the critical component ofthe analysis and allows the demonstration of a new approach toatomistic impurity metrology.

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• 83:

  Title: Rahman R; Nielsen E; Muller RP; Carroll MS, 2012, 'Voltage controlled exchange energies of a two-electron silicon double quantum dot with and without charge defects in the dielectric', Physical Review B - Condensed Matter and Materials Physics, vol. 85
     

  Year : 2012

  Publication Type: Journal Papers

  Topic:

  Abstract

  Quantum dots are artificial atoms used for a multitude of purposes. Charge defects are commonly present and can significantly perturb the designed energy spectrum and purpose of the dots. Voltage controlled exchange energy in silicon double quantum dots (DQDs) represents a system that is very sensitive to charge position and is of interest for quantum computing. We calculate the energy spectrum of the silicon double quantum dot system using a full configuration interaction that uses tight-binding single-particle wave functions. This approach allows us to analyze atomic scale charge perturbations of the DQD while accounting for the details of the complex momentum space physics of silicon (i.e., valley and valley-orbit physics). We analyze how the energy levels and exchange curves for a DQD are affected by nearby charge defects at various positions relative to the dot, which are consistent with defects expected in the metal-oxide-semiconductor system.

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• 84:

  Title: Witzel WM; Rahman R; Carroll MS, 2012, 'Nuclear spin induced decoherence of a quantum dot in Si confined at a SiGe interface: Decoherence dependence on 73Ge', Physical Review B - Condensed Matter and Materials Physics, vol. 85
     

  Year : 2012

  Publication Type: Journal Papers

  Topic:

  Abstract

  We theoretically study the nuclear spin induced decoherence of a quantum dot in Si that is confined at a SiGe interface. We calculate decoherence time dependence on 73 Ge in the barrier layer to evaluate the importance of Ge as well as Si enrichment for long decoherence times. We use atomistic tight-binding modeling for an accurate account of the electron wave function which is particularly important for determining the contact hyperfine interactions with the Ge nuclear spins. We find decoherence times due to Ge spins at natural concentrations to be milliseconds. This suggests that SiGe/Si quantum dot devices employing enriched Si will require enriched Ge as well in order to benefit from long coherence times. We provide a comparison of T 2 times for various fractions of nonzero spin isotopes of Si and Ge.

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• 85:

  Title: Neupane MR; Lake RK; Rahman R, 2012, 'Electronic states of Ge/Si nanocrystals with crescent-shaped Ge-cores', Journal of Applied Physics, vol. 112
     

  Year : 2012

  Publication Type: Journal Papers

  Topic:

  Abstract

  Ge/Si nanocrystals can serve as charge storage sites in a nanocrystal memory by providing a hole quantum-well in the Ge region. The electronic states of realistically shaped Ge/Si nanocrystals with crescent-shaped Ge-cores are calculated to determine the hole confinement energies, effective masses, barrier heights, and thermionic lifetimes. As the Ge crescent thickness increases from 1 nm to 3.5 nm, the hole confinement energy decreases from 0.52 to 0.28 eV, the barrier height to escape into the Si valence band increases from 0.25 to 0.51 eV, and the resulting thermionic hole lifetime increases from 10−9 to 10−5 s. The nanocrystals are modeled with an atomistic, 20-band sp3d5s* tight-binding model including spin-orbit coupling as implemented in NEMO3D. Geometry relaxation and strain are included using the valence-force-field model with Keating potentials.

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• 86:

  Title: Nielsen E; Rahman R; Muller RP, 2012, 'A many-electron tight binding method for the analysis of quantum dot systems', Journal of Applied Physics, vol. 112
     

  Year : 2012

  Publication Type: Journal Papers

  Topic:

  Abstract

  We present a method which computes many-electron energies and eigenfunctions by a full configuration interaction, which uses a basis of atomistic tight-binding wave functions. This approach captures electron correlation as well as atomistic effects, and is well suited to solid state quantum dot systems containing few electrons, where valley physics and disorder contribute significantly to device behavior. Results are reported for a two-electron silicon double quantum dot as an example.

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• 87:

  Title: Lansbergen G; Rahman R; Verduijn A; Tettamanzi G; Collaert N; Biesemans S; Klimeck G; Rogge S; Hollenberg L, 2011, 'Lifetime-enhanced transport in silicon due to spin and valley blockade', Physical Review Letters, vol. 107, pp. 136602-1 - 136602-5
     

  Year : 2011

  Publication Type: Journal Papers

  Topic:

  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 to 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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• 88:

  Title: Rahman R; Verduijn JA; Kharche N; Lansbergen G; Klimeck ; Hollenberg ; Rogge S, 2011, 'Engineered valley-orbit splittings in quantum-confined nanostructures in silicon', Physical Review B, vol. 83, pp. 195323-1 - 195323-5
     

  Year : 2011

  Publication Type: Journal Papers

  Topic:

  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

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• 89:

  Title: Rahman ; Lansbergen ; Verduijn A; Tettamanzi G; Park ; Collaert ; Biesemans ; Klimeck ; Hollenberg ; Rogge S, 2011, 'Electric field reduced charging energies and two-electron bound excited states of single donors in silicon', Physical Review B, vol. 84, pp. 115458-1 - 115458-7
     

  Year : 2011

  Publication Type: Journal Papers

  Topic:

  Abstract

  We present atomistic simulations of the D 0 to D − charging energies of a gated donor in silicon as a function of applied fields and donor depths and find good agreement with experimental measurements. A self-consistent field large-scale tight-binding method is used to compute the D − binding energies with a domain of over 1.4 million atoms, taking into account the full band structure of the host, applied fields, and interfaces. An applied field pulls the loosely bound D − electron toward the interface and reduces the charging energy significantly below the bulk values. This enables formation of bound excited D − states in these gated donors, in contrast to bulk donors. A detailed quantitative comparison of the charging energies with transport spectroscopy measurements with multiple samples of arsenic donors in ultrascaled metal-oxide-semiconductor transistors validates the model results and provides physical insights. We also report measured D − data showing the presence of bound D − excited states under applied fields.

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• 90:

  Title: Rahman R; Park SH; Klimeck G; Hollenberg LCL, 2011, 'Stark tuning of the charge states of a two-donor molecule in silicon', Nanotechnology, vol. 22
     

  Year : 2011

  Publication Type: Journal Papers

  Topic:

  Abstract

  A singly ionized two-donor molecule in silicon is an interesting test-bed system for implementing a quantum bit using charge degrees of freedom at the atomic limit of device fabrication. The operating principles of such a device are based on wavefunction symmetries defined by charge localizations and energy gaps in the spectrum. The Stark-shifted electronic structure of a two-donor phosphorus molecule is investigated using a multi-million-atom tight-binding framework. The effects of surface (S) and barrier (B) gates are analyzed for various voltage regimes. It is found that gate control is smooth for any donor separation, although at certain donor orientations the S and B gates may alter in functionality. Effects such as interface ionization, saturation of the lowest energy gap, and sensitivity to donor and gate placements are also investigated. Excited molecular states of P2 + are found to impose limits on the allowed donor separations and operating gate voltages for coherent operation. This work therefore outlines and analyzes the various issues that are of importance in the design and control of such donor molecular systems.

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