| 1. |
- Ellström, Carl, et al.
(författare)
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Exciton fine structure splitting in InP quantum dots in GaInP
- 2007
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 19:29
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electronic structure of excitons in InP quantum dots in GaInP. The exciton is theoretically expected to have four states. Two of the states are allowed to optically decay to the ground ( vacuum) state in the dipole approximation. We see these two lines in photoluminescence (PL) experiments and find that the splitting between the lines ( the fine structure splitting) is 150(+/- 30) mu eV. The lines were perpendicularly polarized. We verified that the lines arise from neutral excitons by using correlation spectroscopy. The theoretical calculations show that the polarization of the emission lines are along and perpendicular to the major axis of elongated dots. The fine structure splitting depends on the degree of elongation of the dots and is close to zero for dots of cylindrical symmetry, despite the influence of the piezoelectric polarization, which is included in the calculation.
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| 2. |
- Ellström, Carl, et al.
(författare)
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Investigations of InAs surface dots on InP
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:3
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated InAs dots on the surface of InP, determined their structure, and measured the optical transition energy. This energy was found to be in excellent agreement with theoretical calculations, where no free parameters have been used. The calculations were performed using eight-band k center dot p theory in the envelope function approximation. We conclude that this theory is adequate to describe quantum dots also when one of the confining materials is vacuum. (c) 2006 American Institute of Physics.
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| 3. |
- Fuhrer, Andreas, et al.
(författare)
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Few electron double quantum dots in InAs/InP nanowire heterostructures
- 2007
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 7:2, s. 243-246
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Tidskriftsartikel (refereegranskat)abstract
- We report on fabrication of double quantum dots in catalytically grown InAs/InP nanowire heterostructures. In the few-electron regime, starting with both dots empty, our low-temperature transport measurements reveal a clear shell structure for sequential charging of the larger of the two dots with up to 12 electrons. The resonant current through the double dot is found to depend on the orbital coupling between states of different radial symmetry. The charging energies are well described by a capacitance model if next-neighbor capacitances are taken into account.
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| 4. |
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| 5. |
- Nakkar, A, et al.
(författare)
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Optical properties and morphology of InAs/InP (113)B surface quantum dots
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:23, s. 3-231911
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Tidskriftsartikel (refereegranskat)abstract
- We report on long-wavelength photoluminescence (PL) emission at room temperature from self-organized InAs surface quantum dots grown by gas-source molecular beam epitaxy on a GaInAsP/InP (113)B substrate. The influence of arsenic pressure conditions during growth on the PL emission of surface quantum dots is detailed as well as oxide/contamination layer formation after growth. Experimental results are in good agreement with six-band k.p theory in the envelope function approximation.
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| 6. |
- Persson, Jonas, et al.
(författare)
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Strain effects on individual quantum dots: Dependence of cap layer thickness
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:8
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the effects of strain on individual self-assembled quantum dots (QDs) exemplified by InP dots embedded in GaInP. The quantum dot sample was etched from the top and in this way the amount of capping material was reduced. In a sequence of etch cycles, the cap layer was thinned, and the photoluminescence from several individual QDs could be followed as a function of cap layer thickness. The evolution of the emission spectra clearly depended on the quantum dot size. We interpret this as arising from differences in the aspect ratio for quantum dots of different sizes. The influence of the capping layer, for different QD geometries, was modeled using deformation potential theory with the strain calculated using a full three-dimensional linear elasticity model. The results agree well with the experimental observations.
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| 7. |
- Pistol, Mats-Erik, et al.
(författare)
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Adiabatic connections and properties of coupling-integrated exchange-correlation holes and pair densities in density functional theory
- 2009
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 480:1-3, s. 136-139
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a method that likely will improve the accuracy of functionals used in density functional theory and pair density functional theory. In deriving the method we show that the coupling-integrated exchange-correlation hole used in density functional theory obeys all the N-representability conditions as non-integrated holes and we give two such conditions, not normally used by the density functional theory community. We will also show that in addition to the normal adiabatic connection there exist a dual adiabatic connection where the kinetic energy is integrated over the inverse electron mass. (C) 2009 Elsevier B.V. All rights reserved.
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| 8. |
- Pistol, Mats-Erik, et al.
(författare)
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Band structure of core-shell semiconductor nanowires
- 2008
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 78:11
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated band structures for strained core-shell nanowires involving all combinations of AlN, GaN, and InN, as well as all combinations of AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb, as functions of core and shell radii. This gives 78 combinations, most of which have not been experimentally realized, and provides a quite complete overview of which interesting structures can be realized in core-shell zinc-blende III-V nanowires. Both the Gamma-and the X-conduction-band minima were included in the calculations in addition to the valence-band maximum. The calculations were performed using continuum elasticity theory for the strain, eight-band strain-dependent k center dot p theory for the Gamma-point energies, and a single-band approximation for the X-point conduction minima. All combinations of materials having type-I, type-II, and type-III (broken gap) band alignments have been identified, as well as all combinations for which one material becomes metallic due to a negative band gap. We identify structures that may support exciton crystals, excitonic superconductivity, and biomolecular detection. We have also computed the effective masses from which the confinement energy may be estimated. While graphical presentation of the results helps identify trends, all the numerical results are also available online.
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| 9. |
- Pistol, Mats-Erik, et al.
(författare)
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Band structure of segmented semiconductor nanowires
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 80:3
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Tidskriftsartikel (refereegranskat)abstract
- We have calculated the band structures for strained segmented nanowires involving all combinations of AlN, GaN, InN, AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb, as a function of segment length. This was done for two different growth directions of the wires, [100] and [111]. Both the Gamma and the X conduction-band minima were included in the calculations as well as the valence bands. Short segments behave like strained quantum wells and our results thus include strained quantum wells as a subset. We find all material combinations that give metallic segments due to a negative band gap and we find all the band alignments that may occur. We identify those structures which show spontaneous charge separation as well as those which are suitable for the optical generation of polarized exciton gases, with their rich phase diagram, theoretically predicted to include superfluids and supersolids. Some device related ideas are presented. Due to the amount of data (several hundreds of diagrams) most of our results are presented as a webpage.
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| 10. |
- Pistol, Mats-Erik
(författare)
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Characterization of N-representable n-particle densities when N is infinite
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 417:4-6, s. 521-523
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Tidskriftsartikel (refereegranskat)abstract
- We have found necessary and sufficient conditions for the n-particle density to be N-representable for infinite A, if n is even. There are some mild restrictions on the one-density for these conditions to apply. The method is based on the Mercer expansion theorem. We suggest a simple method for total energy calculations based on this characterization also if the number of particles is finite. (c) 2005 Elsevier B.V. All rights reserved.
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