Fermi-level pinning can determine polarity in semiconductor nanorods

Avraam, Philip; Hine, Nicholas; Tangney, Paul; Haynes, Peter

doi:10.1103/physrevb.85.115404

Cited by 18 publications

(18 citation statements)

References 34 publications

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“…Using linear-scaling DFT (ref. 34), as implemented in the ONETEP method [35][36][37] , which captures charge redistribution effects both efficiently and accurately 38,39 , we have performed simulations on structures containing 5,000 and 12,168 atoms (one of the largest fully self-consistent calculations ever performed). The 5,000 atom calculation was carried out by iteratively refining a compact real-space Wannier basis with respect to a primary plane-wave basis, whereas in the 12,168 atom calculation the real-space basis was pre-optimized for isolated atoms, and thereafter fixed.…”

Section: Methodsmentioning

confidence: 99%

Self-assembled quantum dots in a nanowire system for quantum photonics

et al. 2013

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Quantum dots embedded within nanowires represent one of the most promising technologies for applications in quantum photonics. Whereas the top-down fabrication of such structures remains a technological challenge, their bottom-up fabrication through self-assembly is a potentially more powerful strategy. However, present approaches often yield quantum dots with large optical linewidths, making reproducibility of their physical properties difficult. We present a versatile quantum-dot-innanowire system that reproducibly self-assembles in core-shell GaAs/AlGaAs nanowires. The quantum dots form at the apex of a GaAs/AlGaAs interface, are highly stable, and can be positioned with nanometre precision relative to the nanowire centre. Unusually, their emission is blue-shifted relative to the lowest energy continuum states of the GaAs core. Large-scale electronic structure calculations show that the origin of the optical transitions lies in quantum confinement due to Al-rich barriers. By emitting in the red and self-assembling on silicon substrates, these quantum dots could therefore become building blocks for solid-state lighting devices and third-generation solar cells. S emiconductor quantum dots have been shown to be excellent building blocks for quantum photonics applications, such as single-photon sources and nano-sensing. Desirable properties of a single-photon emitter include high-fidelity anti-bunching (very small g 2 (t = 0)), narrow emission lines (ideally transform limited to a few microelectronvolt) and high brightness (>1 MHz count rate on standard detector). For simplicity, these properties should be achieved either with electrical injection or non-resonant optical excitation. Desirable properties of a nano-sensor include a high sensitivity to local electric and magnetic fields, with the quantum dot located as close as possible to the target region. A popular realization involves Stranski-Krastanow InGaAs quantum dots embedded in a three-dimensional matrix, which are excellent building blocks for the realization of practical singlephoton sources 1 . However, the photon extraction out of the bulk semiconductor is highly inefficient on account of the large mismatch in refractive indices of GaAs and vacuum. An attractive way forward is to embed the quantum dots in a nanowire 2 . To solve the extraction problem, the nanowire is designed to operate as a single-mode waveguide, a so-called photonic nanowire, with a taper as photon out-coupler 3 . Also, for nano-sensing applications, a quantum dot in a nanowire can be located much closer to the active medium. Top-down fabrication of the photonic waveguide is technologically complex, however. Bottom-up fabrication of the photonic waveguide is very attractive 4-6 , but it is at present challenging to self-assemble quantum dots in the nanowires with narrow linewidths and high yields 7,8 . Nano-sensing applications are at present not highly developed. Other degrees of freedom of the quantum-dot-in-nanowire system that can be usefully exploited are the mechanical modes ...

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Section: Methodsmentioning

confidence: 99%

Self-assembled quantum dots in a nanowire system for quantum photonics

et al. 2013

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“…Analogous to the concept of Fermi-level pinning in polar semiconductor nanorods, where the Fermi energy coincides with a finite density of states at either end of the rods [43,44], the Fermi energy coincides with a non-zero density of states on opposite surfaces of the water cluster. We expect the HOMO-LUMO gap to disappear completely when the radius of the water cluster increases to the point where the variation of the surface potential is of sufficient magnitude to bridge the gap.…”

Section: Water Clustersmentioning

confidence: 99%

Electrostatic considerations affecting the calculated HOMO–LUMO gap in protein molecules

Lever¹,

Cole

Hine

et al. 2013

J. Phys.: Condens. Matter

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A detailed study of energy differences between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gaps) in protein systems and water clusters is presented. Recent work questioning the applicability of Kohn-Sham density-functional theory to proteins and large water clusters (Rudberg 2012 J. Phys.: Condens. Matter 24 072202) has demonstrated vanishing HOMO-LUMO gaps for these systems, which is generally attributed to the treatment of exchange in the functional used. The present work shows that the vanishing gap is, in fact, an electrostatic artefact of the method used to prepare the system. Practical solutions for ensuring the gap is maintained when the system size is increased are demonstrated. This work has important implications for the use of large-scale density-functional theory in biomolecular systems, particularly in the simulation of photoemission, optical absorption and electronic transport, all of which depend critically on differences between energies of molecular orbitals.S Online supplementary data available from stacks.iop.org/JPhysCM/25/152101/mmedia

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“…This can be addressed by working with a linear-scaling DFT code such as ONETEP, 17 for which the favorable balance of cost and accuracy allows the investigation of nanocrystals with many thousands of atoms. 18,19 Even then, the challenge persists of modelling the pressure transmission between solvent molecules and nanocrystalsin analogy to experiments where nanocrystals are dissolved and placed under pressure in a diamond anvil cell. The many degrees of freedom comprising realistic solvents and the many solvent-nanocrystal collisions that need to be averaged over to sample the appropriate thermodynamic ensemble exclude a full ab initio treatment.…”

Section: Introductionmentioning

confidence: 99%

Simulations of nanocrystals under pressure: Combining electronic enthalpy and linear-scaling density-functional theory

Corsini

Greco

Hine

et al. 2013

The Journal of Chemical Physics

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We present an implementation in a linear-scaling density-functional theory code of an electronic enthalpy method, which has been found to be natural and efficient for the ab initio calculation of finite systems under hydrostatic pressure. Based on a definition of the system volume as that enclosed within an electronic density isosurface [M. Cococcioni, F. Mauri, G. Ceder, and N. Marzari, Phys. Rev. Lett. 94, 145501 (2005)], it supports both geometry optimizations and molecular dynamics simulations. We introduce an approach for calibrating the parameters defining the volume in the context of geometry optimizations and discuss their significance. Results in good agreement with simulations using explicit solvents are obtained, validating our approach. Size-dependent pressure-induced structural transformations and variations in the energy gap of hydrogenated silicon nanocrystals are investigated, including one comparable in size to recent experiments. A detailed analysis of the polyamorphic transformations reveals three types of amorphous structures and their persistence on depressurization is assessed.

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Fermi-level pinning can determine polarity in semiconductor nanorods

Cited by 18 publications

References 34 publications

Self-assembled quantum dots in a nanowire system for quantum photonics

Self-assembled quantum dots in a nanowire system for quantum photonics

Electrostatic considerations affecting the calculated HOMO–LUMO gap in protein molecules

Simulations of nanocrystals under pressure: Combining electronic enthalpy and linear-scaling density-functional theory

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