All pulications (111)
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31: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. 6Year : 2016
Publication Type: Journal Papers
Topic:
Abstract
Corrigendum: Characterizing Si:P quantum dot qubits with spin resonance techniques
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32: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. 2Year : 2016
Publication Type: Journal Papers
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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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33:Title: Ilatikhameneh H; Klimeck G; Rahman R, 2016, 'Can Homojunction Tunnel FETs Scale below 10 nm?', IEEE Electron Device Letters, vol. 37, pp. 115 - 118Year : 2016
Publication Type: Journal Papers
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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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34: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. 7Year : 2016
Publication Type: Journal Papers
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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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35: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 - 128Year : 2016
Publication Type: Journal Papers
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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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36:Title: Ameen TA; Ilatikhameneh H; Klimeck G; Rahman R, 2016, 'Few-layer phosphorene: An ideal 2D material for tunnel transistors', Scientific Reports, vol. 6Year : 2016
Publication Type: Journal Papers
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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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37:Title: Ilatikhameneh H; Ameen TA; Klimeck G; Rahman R, 2016, 'Universal Behavior of Atomistic Strain in Self-Assembled Quantum Dots', IEEE Journal of Quantum Electronics, vol. 52Year : 2016
Publication Type: Journal Papers
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Abstract
Self-assembled quantum dots (QDs) are highly strained heterostructures. The lattice strain significantly modifies the electronic and optical properties of these devices. A universal behavior is observed in atomistic strain simulations (in terms of both strain magnitude and profile) of QDs with different shapes and materials. In this paper, this universal behavior is investigated by atomistic as well as analytic continuum models. Atomistic strain simulations are very accurate but computationally expensive. On the other hand, analytic continuum solutions are based on assumptions that significantly reduce the accuracy of the strain calculations, but are very fast. Both techniques indicate that the strain depends on the aspect ratio (AR) of the QDs, and not on the individual dimensions. Thus, simple closed-form equations are introduced which directly provide the atomistic strain values inside the QD as a function of the AR and the material parameters. Moreover, the conduction and valence band edges E C/V and their effective masses m* C/V of the QDs are dictated by the strain and AR consequently. The universal dependence of atomistic strain on the AR is useful in many ways. Not only does it reduce the computational cost of atomistic simulations significantly, but it also provides information about the optical transitions of QDs given the knowledge of E C/V and m* C/V from AR. Finally, these expressions are used to calculate optical transition wavelengths in InAs/GaAs QDs, and the results agree well with the experimental measurements and atomistic simulations.
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38:Title: Ilatikhameneh H; Salazar RB; Klimeck G; Rahman R; Appenzeller J, 2016, 'From Fowler-Nordheim to Nonequilibrium Green's Function Modeling of Tunneling', IEEE Transactions on Electron Devices, vol. 63, pp. 2871 - 2878Year : 2016
Publication Type: Journal Papers
Topic:
Abstract
In this paper, an analytic model is proposed, which provides, in a continuous manner, the current–voltage ( $I$ – $V$ ) characteristic of high-performance tunneling FETs (TFETs) based on direct bandgap semiconductors. The model provides the closed-form expressions for $I$ – $V$ based on: 1) a modified version of the well-known Fowler–Nordheim (FN) formula (in the ON-state) and 2) an equation that describes the OFF-state performance while providing continuity at the ON/OFF threshold by means of a term introduced as the continuity factor. It is shown that the traditional approaches, such as FN, are accurate in TFETs only through correct evaluation of the total band bending distance and the tunneling effective mass. General expressions for these two key parameters are provided. Moreover, it is demonstrated that the tunneling effective mass captures both the ellipticity of evanescent states and the dual (electron/hole) behavior of the tunneling carriers, and it is further shown that such a concept is even applicable to semiconductors with nontrivial energy dispersion. Ultimately, it is found that the $I$ – $V$ characteristics obtained by using this model are in close agreement with the state-of-the-art quantum transport simulations both in the ON- and OFF-state, thus providing the validation of the analytic approach
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39:Title: Mohiyaddin FA; Kalra R; Laucht A; Rahman R; Klimeck G; Morello A, 2016, 'Transport of spin qubits with donor chains under realistic experimental conditions', Physical Review B, vol. 94Year : 2016
Publication Type: Journal Papers
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Abstract
The ability to transport quantum information across some distance can facilitate the design and operation of a quantum processor. One-dimensional spin chains provide a compact platform to realize scalable spin transport for a solid-state quantum computer. Here, we model odd-sized donor chains in silicon under a range of experimental nonidealities, including variability of donor position within the chain. We show that the tolerance against donor placement inaccuracies is greatly improved by operating the spin chain in a mode where the electrons are confined at the Si- SiO 2 interface. We then estimate the required time scales and exchange couplings, and the level of noise that can be tolerated to achieve high-fidelity transport. We also propose a protocol to calibrate and initialize the chain, thereby providing a complete guideline for realizing a functional donor chain and utilizing it for spin transport.
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40:Title: Ilatikhameneh H; Ameen T; Novakovic B; Tan Y; Klimeck G; Rahman R, 2016, 'Saving Moore's Law Down to 1 nm Channels with Anisotropic Effective Mass', Scientific Reports, vol. 6Year : 2016
Publication Type: Journal Papers
Topic:
Abstract
Scaling transistors’ dimensions has been the thrust for the semiconductor industry in the last four decades. However, scaling channel lengths beyond 10 nm has become exceptionally challenging due to the direct tunneling between source and drain which degrades gate control, switching functionality, and worsens power dissipation. Fortunately, the emergence of novel classes of materials with exotic properties in recent times has opened up new avenues in device design. Here, we show that by using channel materials with an anisotropic effective mass, the channel can be scaled down to 1 nm and still provide an excellent switching performance in phosphorene nanoribbon MOSFETs. To solve power consumption challenge besides dimension scaling in conventional transistors, a novel tunnel transistor is proposed which takes advantage of anisotropic mass in both ON- and OFF-state of the operation. Full-band atomistic quantum transport simulations of phosphorene nanoribbon MOSFETs and TFETs based on the new design have been performed as a proof.
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