Multimillion Atom Simulations with Nemo3D

Ahmed, Shaikh; Kharche, Neerav; Rahman, Rajib; Usman, Muhammad; Lee, Sunhee; Ryu, Hoon; Bae, Hagyoul; Clark, Steve; Haley, Benjamin P; Naumov, Maxim; Saied, Faisal; Korkusiński, Marek; Kennel, Rick; McLennan, Michael; Boykin, Timothy B.; Klimeck, Gerhard

doi:10.1007/978-0-387-30440-3_343

Cited by 39 publications

(34 citation statements)

References 94 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We now include central-cell correction at the donor site as a cut-off potential U 0 which is tuned to be 2.6342 eV to accurately reproduce the experimental ground state energy, A 1 =53.1 meV. Further tuning of the onsite TB d−orbital energies [26] allowed to match the experimental excited state energies (T 2 and E) as listed in table I. By applying this model, we compute the value of |ψ(r 0 )| 2 at the donor nuclear site as 4.05 × 10 30 , which comes out to be ≈ 2.34 times larger than the experimental value.…”

Section: Screening Of Donor Potential By Static Dielectric Constantmentioning

confidence: 99%

Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory

Usman

Rahman

Salfi

et al. 2015

J. Phys.: Condens. Matter

Self Cite

View full text Add to dashboard Cite

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 (η2) from -1.3 × 10 −3 µm 2 /V 2 for the static dielectric screening to -1.72 × 10 −3 µm 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 η2 to -1.87 × 10 −3 µm 2 /V 2 , resulting in an excellent agreement of theory with the experimentally measured value of -1.9 ± 0.2 × 10 −3 µm 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.

show abstract

Section: Screening Of Donor Potential By Static Dielectric Constantmentioning

confidence: 99%

Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory

Usman

Rahman

Salfi

et al. 2015

J. Phys.: Condens. Matter

Self Cite

View full text Add to dashboard Cite

show abstract

“…The magnitude of the electric fields is varied between 0 and 45 KV/cm, which is in accordance with the range of the electric fields recently investigated in an experimental study for the design of solar cell devices [25]. The atomistic simulations are performed using nanoelectronic modeling tool NEMO-3D [42][43][44]. published experiments.…”

Section: − Theoretical Frameworkmentioning

confidence: 85%

Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules

Usman

2015

Nanoscale

View full text Add to dashboard Cite

Strongly-coupled quantum dot molecules (QDMs) are widely deployed in the design of a variety of optoelectronic, photovoltaic, and quantum information devices. An efficient and optimized performance of these devices demands engineering of the electronic and optical properties of the underlying QDMs. The application of electric fields offers a knob to realise such control over the QDM characteristics for a desired device operation. We perform multi-million-atom atomistic tight-binding calculations to study the influence of electric fields on the electron and hole wave function confinements and symmetries, the ground-state transition energies, the band-gap wavelengths, and the optical transition modes. The electrical fields both parallel ( E p ) and anti-parallel ( E a ) to the growth direction are investigated to provide a comprehensive guide on the understanding of the electric field effects. The strain-induced asymmetry of the hybridized electron states is found to be weak and can be balanced by applying a small E a electric field, of the order of 1 KV/cm. The strong interdot couplings completely break down at large electric fields, leading to single QD states confined at the opposite edges of the QDM. This mimics a transformation from a type-I band structure to a type-II band structure for the QDMs, which is a critical requirement for the design of intermediate-band solar cells (IBSC). The analysis of the field-dependent ground-state transition energies reveal that the QDM can be operated both as a high dipole moment device by applying large electric fields and as a high polarizibility device under the application of small electric field magnitudes. The quantum confined Stark effect (QCSE) red shifts the band-gap wavelength to 1.3 µm at the 15 KV/cm electric field; however the reduced electron-hole wave function overlaps lead to a decrease in the interband optical transition strengths by roughly three orders of magnitude. The study of the polarisation-resolved optical modes indicate the benefit of applying small electric fields, which lead to an isotropic polarisation response, a desirable property for the semiconductor optical amplifiers (SOAs).1 arXiv:1508.05981v1 [cond-mat.mes-hall]

show abstract

“…The non-spherical nature of the doping potential will be important for calculation of electron-dopant scattering cross sections. Effective mass models of doped silicon assume a spherical Coulomb potential, while some tight binding models use a spherical, Coulomb-like doping potential [28,29,56,57] and allow the surrounding atoms' electronic structure to adjust according to this potential. The anisotropic doping potentials and cell geometries calculated here could be used as alternative parameterizations for tight binding models, and they can also be used to calibrate the resulting potentials and densities calculated by tight binding models.…”

Section: A Doping Potentialmentioning

confidence: 99%

Large-scale atomistic density functional theory calculations of phosphorus-doped silicon quantum bits

2013

View full text Add to dashboard Cite

We present density functional theory calculations of phosphorus dopants in bulk silicon and of several properties relating to their use as spin qubits for quantum computation. Rather than a mixed pseudopotential or a Heitler-London approach, we have used an explicit treatment for the phosphorus donor and examined the detailed electronic structure of the system as a function of the isotropic doping fraction, including lattice relaxation due to the presence of the impurity. Doping electron densities (ρ doped − ρ bulk ) and spin densities (ρ ↑ − ρ ↓ ) are examined in order to study the properties of the dopant electron as a function of the isotropic doping fraction. Doping potentials (V doped − V bulk ) are also calculated for use in calculations of the scattering cross-sections of the phosphorus dopants, which are important in the understanding of electrically detected magnetic resonance experiments. We find that the electron density around the dopant leads to non-spherical features in the doping potentials, such as trigonal lobes in the (001) plane at energy scales of +12 eV near the nucleus and of -700 meV extending away from the dopants. These features are generally neglected in effective mass theory and will affect the coupling between the donor electron and the phosphorus nucleus. Our density functional calculations reveal detail in the densities and potentials of the dopants which are not evident in calculations that do not include explicit treatment of the phosphorus donor atom and relaxation of the crystal lattice. These details can also be used to parameterize tight-binding models for simulation of large-scale devices.

show abstract

Multimillion Atom Simulations with Nemo3D

Cited by 39 publications

References 94 publications

Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory

Donor hyperfine Stark shift and the role of central-cell corrections in tight-binding theory

Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules

Large-scale atomistic density functional theory calculations of phosphorus-doped silicon quantum bits

Contact Info

Product

Resources

About