Journal Papers (79)

• 31:

  Title: Usman M; Bocquel J; Salfi J; Voisin B; Tankasala A; Rahman R; Simmons MY; Rogge S; Hollenberg LCL, 2016, 'Spatial metrology of dopants in silicon with exact lattice site precision', Nature Nanotechnology, vol. 11, pp. 763 - 768
     

  Year : 2016

  Publication Type: Journal Papers

  Topic:

  Abstract

  Scaling of Si-based nanoelectronics has reached the regime where device function is affected not only by the presence of individual dopants, but also by their positions in the crystal. Determination of the precise dopant location is an unsolved problem in applications from channel doping in ultrascaled transistors to quantum information processing. Here, we establish a metrology combining low-temperature scanning tunnelling microscopy (STM) imaging and a comprehensive quantum treatment of the dopant–STM system to pinpoint the exact coordinates of the dopant in the Si crystal. The technique is underpinned by the observation that STM images contain atomic-sized features in ordered patterns that are highly sensitive to the STM tip orbital and the absolute dopant lattice site. The demonstrated ability to determine the locations of P and As dopants to 5 nm depths will provide critical information for the design and optimization of nanoscale devices for classical and quantum computing applications.

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• 32:

  Title: Wang Y; Chen C-Y; Klimeck G; Simmons MY; Rahman R, 2016, 'Characterizing Si:P quantum dot qubits with spin resonance techniques (vol 6, 31830, 2016)', SCIENTIFIC REPORTS, vol. 6
     

  Year : 2016

  Publication Type: Journal Papers

  Topic:

  Abstract

  Corrigendum: Characterizing Si:P quantum dot qubits with spin resonance techniques

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• 33:

  Title: Wang Y; Tankasala A; Hollenberg LCL; Klimeck G; Simmons MY; Rahman R, 2016, 'Highly tunable exchange in donor qubits in silicon', npj Quantum Information, vol. 2
     

  Year : 2016

  Publication Type: Journal Papers

  Topic:

  Abstract

  In this article we have investigated the electrical control of the exchange coupling (J) between donor-bound electrons in silicon with a detuning gate bias, crucial for the implementation of the two-qubit gate in a silicon quantum computer. We found that the asymmetric 2P–1P system provides a highly tunable exchange curve with mitigated J-oscillation, in which 5 orders of magnitude change in the exchange coupling can be achieved using a modest range of electric field (3 MV/m) for ~15-nm qubit separation. Compared with the barrier gate control of exchange in the Kane qubit, the detuning gate design reduces the gate density by a factor of ~2. By combining large-scale atomistic tight-binding method with a full configuration interaction technique, we captured the full two-electron spectrum of gated donors, providing state-of-the-art calculations of exchange energy in 1P–1P and 2P–1P qubits.

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• 34:

  Title: Ilatikhameneh H; Klimeck G; Rahman R, 2016, 'Can Homojunction Tunnel FETs Scale below 10 nm?', IEEE Electron Device Letters, vol. 37, pp. 115 - 118
     

  Year : 2016

  Publication Type: Journal Papers

  Topic:

  Abstract

  The main promise of tunnel FETs (TFETs) is to enable supply voltage (V DD ) scaling in conjunction with dimension scaling of transistors to reduce power consumption. However, reducing V DD and channel length (L ch ) typically deteriorates the ON- and OFF-state performance of TFETs, respectively. Accordingly, there is not yet any report of a high-performance TFET with both low V DD (~0.2 V) and small L ch (~6 nm). In this letter, it is shown that scaling TFETs in general requires scaling down the bandgap Eg and scaling up the effective mass m* for high performance. Quantitatively, a channel material with an optimized bandgap (E g ~ 1.2qV DD [eV]) and an engineered effective mass (m* -1 ~ 40V DD 2.5 [m 0 -1 ]) makes both V DD and L ch scaling feasible with the scaling rule of L ch /V DD = 30 nm/V for L ch from 15 to 6 nm and the corresponding V DD from 0.5 to 0.2 V.

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• 35:

  Title: Salfi J; Mol JA; Rahman R; Klimeck G; Simmons MY; Hollenberg LCL; Rogge S, 2016, 'Quantum simulation of the Hubbard model with dopant atoms in silicon', Nature Communications, vol. 7
     

  Year : 2016

  Publication Type: Journal Papers

  Topic:

  Abstract

  In quantum simulation, many-body phenomena are probed in controllable quantum systems. Recently, simulation of Bose–Hubbard Hamiltonians using cold atoms revealed previously hidden local correlations. However, fermionic many-body Hubbard phenomena such as unconventional superconductivity and spin liquids are more difficult to simulate using cold atoms. To date the required single-site measurements and cooling remain problematic, while only ensemble measurements have been achieved. Here we simulate a two-site Hubbard Hamiltonian at low effective temperatures with single-site resolution using subsurface dopants in silicon. We measure quasi-particle tunnelling maps of spin-resolved states with atomic resolution, finding interference processes from which the entanglement entropy and Hubbard interactions are quantified. Entanglement, determined by spin and orbital degrees of freedom, increases with increasing valence bond length. We find separation-tunable Hubbard interaction strengths that are suitable for simulating strongly correlated phenomena in larger arrays of dopants, establishing dopants as a platform for quantum simulation of the Hubbard model.

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• 36:

  Title: Chen FW; Ilatikhameneh H; Klimeck G; Chen Z; Rahman R, 2016, 'Configurable Electrostatically Doped High Performance Bilayer Graphene Tunnel FET', IEEE Journal of the Electron Devices Society, vol. 4, pp. 124 - 128
     

  Year : 2016

  Publication Type: Journal Papers

  Topic:

  Abstract

  A bilayer graphene-based electrostatically doped tunnel field-effect transistor (BED-TFET) is proposed. Unlike graphene nanoribbon TFETs in which the edge states deteriorate the OFF-state performance, BED-TFETs operate based on bandgaps induced by vertical electric fields in the source, channel, and drain regions without any chemical doping. The performance of the transistor is evaluated by self-consistent quantum transport simulations. This device has several advantages: 1) ultra-low power (V DD =0.1 V); 2) high performance (I ON /I OFF >10 4 ); 3) steep subthreshold swing (SS<;10mv/dec); and 4) electrically configurable between N-TFET and P-TFET post fabrication. The operation principle of the BED-TFET and its performance sensitivity to the device design parameters are presented

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• 37:

  Title: Ameen TA; Ilatikhameneh H; Klimeck G; Rahman R, 2016, 'Few-layer phosphorene: An ideal 2D material for tunnel transistors', Scientific Reports, vol. 6
     

  Year : 2016

  Publication Type: Journal Papers

  Topic:

  Abstract

  2D transition metal dichalcogenides (TMDs) have attracted a lot of attention recently for energy-efficient tunneling-field-effect transistor (TFET) applications due to their excellent gate control resulting from their atomically thin dimensions. However, most TMDs have bandgaps (Eg) and effective masses (m*) outside the optimum range needed for high performance. It is shown here that the newly discovered 2D material, few-layer phosphorene, has several properties ideally suited for TFET applications: 1) direct Eg in the optimum range ~1.0–0.4 eV, 2) light transport m* (0.15 m0), 3) anisotropic m* which increases the density of states near the band edges and 4) a high mobility. These properties combine to provide phosphorene TFET outstanding ION ~ 1 mA/um, ON/OFF ratio ~ 106 for a 15 nm channel and 0.5 V supply voltage, thereby significantly outperforming the best TMD-TFETs and CMOS in many aspects such as ON/OFF current ratio and energy-delay products. Furthermore, phosphorene TFETS can scale down to 6 nm channel length and 0.2 V supply voltage within acceptable range in deterioration of the performance metrics. Full-band atomistic quantum transport simulations establish phosphorene TFETs as serious candidates for energy-efficient and scalable replacements of MOSFETs.

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• 38:

  Title: Salazar RB; Ilatikhameneh H; Rahman R; Klimeck G; Appenzeller J, 2015, 'A predictive analytic model for high-performance tunneling field-effect transistors approaching non-equilibrium Green's function simulations', Journal of Applied Physics, vol. 118
     

  Year : 2015

  Publication Type: Journal Papers

  Topic:

  Abstract

  A new compact modeling approach is presented which describes the full current-voltage (I-V) characteristic of high-performance (aggressively scaled-down) tunneling field-effect-transistors (TFETs) based on homojunction direct-bandgap semiconductors. The model is based on an analytic description of two key features, which capture the main physical phenomena related to TFETs: (1) the potential profile from source to channel and (2) the elliptic curvature of the complex bands in the bandgap region. It is proposed to use 1D Poisson's equations in the source and the channel to describe the potential profile in homojunction TFETs. This allows to quantify the impact of source/drain doping on device performance, an aspect usually ignored in TFET modeling but highly relevant in ultra-scaled devices. The compact model is validated by comparison with state-of-the-art quantum transport simulations using a 3D full band atomistic approach based on non-equilibrium Green's functions. It is shown that the model reproduces with good accuracy the data obtained from the simulations in all regions of operation: the on/off states and the n/p branches of conduction. This approach allows calculation of energy-dependent band-to-band tunneling currents in TFETs, a feature that allows gaining deep insights into the underlying device physics. The simplicity and accuracy of the approach provide a powerful tool to explore in a quantitatively manner how a wide variety of parameters (material-, size-, and/or geometry-dependent) impact the TFET performance under any bias conditions. The proposed model presents thus a practical complement to computationally expensive simulations such as the 3D NEGF approach.

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• 39:

  Title: Ilatikhameneh H; Tan Y; Novakovic B; Klimeck G; Rahman R; Appenzeller J, 2015, 'Tunnel Field-Effect Transistors in 2-D Transition Metal Dichalcogenide Materials', IEEE Journal on Exploratory Solid-State Computational Devices and Circuits, vol. 1, pp. 12 - 18
     

  Year : 2015

  Publication Type: Journal Papers

  Topic:

  Abstract

  In this paper, the performance of tunnel field-effect transistors (TFETs) based on 2-D transition metal dichalcogenide (TMD) materials is investigated by atomistic quantum transport simulations. One of the major challenges of TFETs is their low ON-currents. 2-D material-based TFETs can have tight gate control and high electric fields at the tunnel junction, and can, in principle, generate high ON-currents along with a subthreshold swing (SS) smaller than 60 mV/decade. Our simulations reveal that high-performance TMD TFETs not only require good gate control, but also rely on the choice of the right channel material with optimum bandgap, effective mass, and source/drain doping level. Unlike previous works, a full-band atomistic tight-binding method is used self-consistently with 3-D Poisson equation to simulate ballistic quantum transport in these devices. The effect of the choice of the TMD material on the performance of the device and its transfer characteristics are discussed. Moreover, the criteria for high ON-currents are explained with a simple analytic model, showing the related fundamental factors. Finally, the SS and energy delay of these TFETs are compared with conventional CMOS devices.

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• 40:

  Title: Li W; Sharmin S; Ilatikhameneh H; Rahman R; Lu Y; Wang J; Yan X; Seabaugh A; Klimeck G; Jena D; Fay P, 2015, 'Polarization-Engineered III-Nitride Heterojunction Tunnel Field-Effect Transistors', IEEE Journal on Exploratory Solid-State Computational Devices and Circuits, vol. 1, pp. 28 - 34
     

  Year : 2015

  Publication Type: Journal Papers

  Topic:

  Abstract

  The concept and simulated device characteristics of tunneling field-effect transistors (TFETs) based on III-nitride heterojunctions are presented for the first time. Through polarization engineering, interband tunneling can become significant in III-nitride heterojunctions, leading to the potential for a viable TFET technology. Two prototype device designs, inline and sidewall-gated TFETs, are discussed. Polarization-assisted p-type doping is used in the source region to mitigate the effect of the deep Mg acceptor level in p-type GaN. Simulations indicate that TFETs based on III-nitride heterojunctions can be expected to achieve ON/OFF ratios of 106 or more, with switching slopes well below 60 mV/decade, ON-current densities approaching 100 μA/μm, and energy delay products as low as 67 aJ-ps/μm.

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