| 1. |
- Geijselaers, Irene, et al.
(författare)
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Atomically sharp, crystal phase defined GaAs quantum dots
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 119:26
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Crystal phase defined heterostructures, or polytype heterostructures, are atomically sharp with no intermixing, which makes them ideal contenders for a wide number of applications. Although polytype quantum dots have shown promising results as single photon sources, a high degree of control on the dimensions and number of polytype quantum dots is necessary before any application can be developed.In this work we show results from optical characterization of highly controlled wz-zb GaAs quantum dots with sharp photoluminescence signal and a strong indication of 0D density of states. One band effective mass calculations show good agreement with the measured data. Radially confined nanowires with a single wz-zb GaAs interface also show sharp photoluminescence signal and a 0D density of states. This indicates the existence of quantum dot like states in the triangular wells formed at the wz-zb GaAs interface. These results show the potential of polytype quantum dots for physics and optics applications.
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| 2. |
- Liu, Tian Xiang, et al.
(författare)
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Coarse-grained tight-binding models
- 2022
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984. ; 34:12
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Tidskriftsartikel (refereegranskat)abstract
- Calculating the electronic structure of systems involving very different length scales presents a challenge. Empirical atomistic descriptions such as pseudopotentials or tight-binding models allow one to calculate the effects of atomic placements, but the computational burden increases rapidly with the size of the system, limiting the ability to treat weakly bound extended electronic states. Here we propose a new method to connect atomistic and quasi-continuous models, thus speeding up tight-binding calculations for large systems. We divide a structure into blocks consisting of several unit cells which we diagonalize individually. We then construct a tight-binding Hamiltonian for the full structure using a truncated basis for the blocks, ignoring states having large energy eigenvalues and retaining states with energies close to the band edge energies. A numerical test using a GaAs/AlAs quantum well shows the computation time can be decreased to less than 5% of the full calculation with errors of less than 1%. We give data for the trade-offs between computing time and loss of accuracy. We also tested calculations of the density of states for a GaAs/AlAs quantum well and find a ten times speedup without much loss in accuracy.
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| 3. |
- Liu, Tian Xiang, et al.
(författare)
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Speeding up tight binding calculations using zone-folding methods
- 2022
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Ingår i: Computational Materials Science. - : Elsevier BV. - 0927-0256. ; 211
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Tidskriftsartikel (refereegranskat)abstract
- Tight binding models are widely used in large scale electronic structure calculations of nanostructures. Their atomistic nature makes them flexible, but also means the computational cost increases rapidly with system size. The large number of calculations required to design nanostructures makes computational efficiency desirable. We have developed a method to increase computational speed while retaining most of its accuracy. The method is based on the use of supercells and zone folding combined with a truncation of the Hamiltonians to only include states close to the band-edges. We apply the method to model the band edge energies of a GaAs/AlAs quantum well grown along the [110]-directions with 3D and 2D periodic boundary conditions as well as the density of states and dielectric function of the quantum well. We typically find a speed-up of ten times with only a small loss of accuracy of the calculation result.
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| 4. |
- Montazeri, Mohammad, et al.
(författare)
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Direct Measure of Strain and Electronic Structure in GaAs/GaP Core-Shell Nanowires
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:3, s. 880-886
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Tidskriftsartikel (refereegranskat)abstract
- Highly strained GaAs/GaP nanowires of excellent optical quality were grown with 50 nm diameter GaAs cores and 25 nm GaP shells. Photoluminescence from these nanowires is observed at energies dramatically shifted from the unstrained GaAs free exciton emission energy by 260 meV. Using Raman scattering, we show that it is possible to separately measure the degree of compressive and shear strain of the GaAs core and show that the Raman response of the GaP shell is consistent with tensile strain. The Raman and photoluminescence measurement are both on good agreement with 8 band k.p calculations, This result opens up new possibilities for engineering the electronic properties of the nanowires for optimal design of one-dimensional nanodevices by controlling the strain of the core and shell by varying the nanowire geometry.
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| 5. |
- Pryor, Craig E., et al.
(författare)
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Atomistic k . p theory
- 2015
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 118:22
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Tidskriftsartikel (refereegranskat)abstract
- Pseudopotentials, tight-binding models, and k p theory have stood for many years as the standard techniques for computing electronic states in crystalline solids. Here, we present the first new method in decades, which we call atomistic k . p theory. In its usual formulation, k . p theory has the advantage of depending on parameters that are directly related to experimentally measured quantities, however, it is insensitive to the locations of individual atoms, We construct an atomistic k . p theory by defining envelope functions on a grid matching the crystal lattice, The model parameters are matrix elements which arc obtained from experimental results or ab natio wave functions in a simple way. This is in contrast to the other atomistic approaches in which parameters are fit to reproduce a desired dispersion and are not expressible in terms of fundamental quantities. This fitting is often very difficult. We illustrate our method by constructing a four-band atomistic model for a diamond/zinchlende crystal and show that it is equivalent to the sp(3) tight-binding model. We can thus directly derive the parameters in the sp(3) tight-binding model from experimental data, We then take the atomistic limit of the widely used eight-hand Kane model and compute the hand structures for all III V semiconductors not containing nitrogen or boron using parameters fit to experimental data. Our new approach extends k . p theory to problems in which atomistic precision is required, such as impurities, alloys, polytypes, and interfaces. It also provides a new approach to multiscale modeling by allowing continuum and atomistic k . p models to he combined in the same system, (C) 2015 AIP Publishing LLC
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| 6. |
- Sköld, Niklas, et al.
(författare)
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Microphotoluminescence studies of tunable wurtzite InAs0.85P0.15 quantum dots embedded in wurtzite InP nanowires
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 80:4
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effects of strong confinement in wurtzite InAs0.85P0.15 quantum dots embedded in wurtzite InP nanowires using microphotoluminescence spectroscopy. Strain-dependent k . p calculations were used to model the quantum dots, and it was found that the electron effective mass was increased by a factor of 2 and the band gap was increased by 190 meV compared to equivalent quantum dots in the zinc-blende polytype. Measurements indicate that there is a relaxation bottleneck giving rise to an anomalous state filling behavior.
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