| 1. |
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| 2. |
- Atlasov, K.A., et al.
(författare)
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Site-controlled single quantum wire integrated into a photonic-crystal membrane microcavity
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90, s. 153107-
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Tidskriftsartikel (refereegranskat)abstract
- Integration of a site-controlled semiconductor V-groove quantum wire (QWR) into a photonic-crystal (PhC) membrane microcavity is reported. Reproducible coupling of the QWR emission to a mode of the PhC cavity is evidenced by the narrower linewidth, higher intensity, and variation with temperature and PhC parameters of the QWR line. Finite difference time domain simulations of the cavity are employed for identifying the observed mode. The presented PhC-QWR coupled structures are promising for achieving very low-threshold lasers and for studies of one-dimensional photon-exciton coupled systems
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Byszewski, M., et al.
(författare)
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Magneto-photoluminescence of heavy- and light-hole excitons in site-controlled pyramidal quantum dots
- 2008
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 40:6, s. 1873-1875
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Tidskriftsartikel (refereegranskat)abstract
- Pyramidal, site-controlled InGaAs/AlGaAs quantum dots (QDs) are studied by micro-photoluminescence (PL) spectroscopy in a magnetic field. The light-hole (LH) excitonic transitions exhibit diamagnetic shifts similar to those of their heavy-hole (HH) counterparts. From the evolution of the excitonic lines, effective g-factors of g=1.7 and 0.4 for HH and LH neutral excitons are inferred
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Optical polarization anisotropy and hole states in pyramidal quantum dots
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89, s. 251113-
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Tidskriftsartikel (refereegranskat)abstract
- The authors present a polarization-resolved photoluminescence study of single semiconductor quantum dots (QDs) interconnected to quantum wires, measured both in a top geometry, and in a less conventional cleaved-edge geometry. Strong polarization anisotropy is revealed for all observed transitions, and it is deduced that closely spaced QD hole states exhibit nearly pure heavy-or light-hole character. These effects are attributed to the large aspect ratio of the dot shape
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| 11. |
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| 12. |
- Leifer, Klaus, et al.
(författare)
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Narrow (= 4 meV) inhomogeneous broadening and its correlation with confinement potential of pyramidal quantum dot arrays
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:8, s. 081106-081106-3
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Tidskriftsartikel (refereegranskat)abstract
- The inhomogeneous broadening in the luminescence spectra of ordered arrays of pyramidal GaAsAlGaAs semiconductor quantum dots (QDs) was studied as a function of the dot size. Dot arrays with inhomogeneous broadening as small as 4.1 meV and a corresponding ground state to first excited state transition separation of 28 meV were obtained. By evaluating the QD energy levels using a multiband kp model, the authors estimated that the observed inhomogeneous broadening corresponds to dot height fluctuations of about 1-2 ML across the array.
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| 13. |
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| 14. |
- Malko, A., et al.
(författare)
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Optimization of the efficiency of single-photon sources based on quantum dots under optical excitation
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88, s. 081905-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate efficient, regulated single-photon operation from site-controlled InGaAs quantum dots (QDs) grown on a prepatterned substrate. Under nonresonant optical excitation, carriers trapped at structural or compositional defects of the adjacent nanostructures led to a degradation of the single-photon statistics from a QD. When the QD was excited quasiresonantly, single photons were emitted and a nearly complete suppression of multiphoton emission was achieved, making these QDs promising candidates for effective solid-state single-photon sources
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| 15. |
- Malko, A., et al.
(författare)
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Single-photon emission from pyramidal quantum dots : The impact of hole thermalization on photon emission statistics
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 72, s. 195332-
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Tidskriftsartikel (refereegranskat)abstract
- We report an experimental study of the emission statistics of excitonic complexes from a single quantum dot and their temperature dependence. The single photon emission from the exciton ground state is shown to persist up to 80 K. The deterioration of single photon statistics is attributed to new biexciton emissions, which emerge in the vicinity of the main single-exciton peak at rising temperatures. We identify these biexcitonic states as being formed by either one hole or two holes occupying excited states and analyze their specific polarization and power-dependent signature.
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| 16. |
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| 17. |
- Pelucchi, E., et al.
(författare)
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Mechanisms of quantum dot energy engineering by metalorganic vapor phase epitaxy on patterned nonplanar substrates
- 2007
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 7:5, s. 1282-1285
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Tidskriftsartikel (refereegranskat)abstract
- A novel technique for tuning the strength of quantum confinement in site-controlled semiconductor quantum dots (QDs) is introduced and investigated theoretically and experimentally. The method makes use of controlled local growth rates during metalorganic vapor phase epitaxy on patterned arrays of inverted pyramids. A model accounting for precursor migration and adatom incorporation predicts the tuning in QD thickness as a function of the pattern parameters. The results are in good agreement with experimental findings. This technique offers means for designing QD photonic structures with potential applications in QD-based cavity quantum electrodynamics and quantum information processing. © 2007 American Chemical Society.
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| 18. |
- Reichardt, H., et al.
(författare)
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Influence of long-range substrate roughness on disorder in V-groove quantum wire structures
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100, s. 123509-
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Tidskriftsartikel (refereegranskat)abstract
- The observation and the interpretation of line splitting in photoluminescence and cathodoluminescence spectra of GaAs/AlGaAs V-groove quantum wires (QWRs) are reported. The QWR emission line splits into two peaks whose intensities oscillate systematically along the axis of the wire. Combining atomic force microscopy and cathodoluminescence measurements, we show a clear correlation between the surface topography of the V-groove and the individual peak intensities. We elucidate the relationship between the V-groove sidewall roughness and the shape at its bottom, and explain their impact on the QWR formation using a two-dimensional growth model accounting for self-limited growth in each V-groove domain. The influence of the long-range substrate roughness on the QWR spectral features is thus clarified. The study provides guidelines for improving QWR uniformity in order to achieve near-ideal model systems for one-dimensional semiconductors
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| 19. |
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| 20. |
- Troncale, V., et al.
(författare)
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Control of valence band states in pyramidal quantum dot-in-dot semiconductor heterostructures
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:24
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Tidskriftsartikel (refereegranskat)abstract
- The character of the hole states in a pyramidal GaAsAlGaAs quantum dot-in-dot (DiD) heterostructure is shown to be controllable by tailoring the confinement potential shape. The change in ground valence band state from heavy hole like to light hole like is demonstrated by side-view polarization resolved photoluminescence measurements. The experimental findings are supported by three-dimensional numerical model calculations. The results are applicable for polarization control in quantum dot photonic devices. © 2007 American Institute of Physics.
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| 21. |
- Troncale, V., et al.
(författare)
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Excited excitonic states observed in semiconductor quantum dots using polarization resolved optical spectroscopy
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101, s. 081703-
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Tidskriftsartikel (refereegranskat)abstract
- We present results on the polarization-resolved photoluminescence emitted from InGaAs/AlGaAs single quantum dots (QDs) grown in inverted tetrahedral pyramids. The emitted light was detected for two mutually perpendicular linear polarization directions in the less conventional cleaved-edge geometry, in addition to the standard top-emission geometry. Whereas the in-plane linear polarization was isotropic, as a consequence of the high symmetry of the system, we found a strong polarization anisotropy of the edge-emitted light revealing QD states of predominantly heavy- or light-hole character. By temperature control of the charge state, several neutral and charged light-hole like exciton complexes were identified. In particular, a biexciton showing a twofold radiative recombination path, leading to two nearly perpendicularly polarized emission multiplets, was identified. These results are also of technological relevance for any design of optoelectronic QD-integrated devices
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| 22. |
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Zhu, Qing, et al.
(författare)
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Alloy segregation, quantum confinement, and carrier capture in self-ordered pyramidal quantum wires
- 2006
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 6:5, s. 1036-1041
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Tidskriftsartikel (refereegranskat)abstract
- The structure and photoluminescence (PL) characteristics of AlGaAs quantum wires self-formed by metallorganic vapor-phase epitaxy in inverted tetrahedral pyramids are reported. Capillarity-driven Ga-Al segregation yields vertical quantum wires (VQWRs) at the center of the pyramid, connected to more-weakly segregated vertical quantum wells (VQWs) formed along their wedges. The segregation is evidenced in transmission electron microscope images and in the PL spectra of these structures. Transitions between quantum-confined electron and hole states in the VQWR are identified in the micro-PL spectra with energies in good agreement with model calculations. The temperature dependence of the micro-PL spectra clearly reveals efficient carrier capture into the VQWR from the VQWs, particularly at an intermediate temperature range ( [similar to] 100 K) where carrier mobility is enhanced. These wires offer new possibilities for tailoring the confinement potential in one-dimensional systems.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
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| 31. |
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| 32. |
- Zhu, Q., et al.
(författare)
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Quantum dot molecules realized with modulated quantum wire heterostructrues
- 2008
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 40:6, s. 1815-1818
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Tidskriftsartikel (refereegranskat)abstract
- We report on double-quantum dot (QD) molecules realized with modulated quantum wire (QWR) heterostructures by self-limiting growth of AlGaAs alloys in inverted tetrahedral pyramids. The QWR barriers connecting the dots facilitate the tunnel-coupling between the confined carriers. Evidences for the presence of such coupling are provided by conventional micro-photoluminescence measurements and theoretical modeling. Systematically tuning the relative QD sizes in the QD molecules reveals spectral line splitting consistent with the expected level splitting due to carrier hybridization. Prospects for extension of these structures to larger QD superlattices are discussed.
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| 33. |
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| 34. |
- Zhu, Q., et al.
(författare)
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Transition from Two-Dimensional to Three-Dimensional Quantum Confinement in Semiconductor Quantum Wires/Quantum Dots
- 2007
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 7:8, s. 2227-2233
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Tidskriftsartikel (refereegranskat)abstract
- We report the photoluminescence (PL) and polarization-resolved PL characteristics of a novel GaAs/AlGaAs quantum wire/dot semiconductor system, realized by metalorganic vapor-phase epitaxy of site-controlled, self-assembled nanostructures in inverted tetrahedral pyramids. By systematically changing the length of the quantum wires, we implement a continuous transition between the regimes of two-dimensional and three-dimensional quantum confinement. The two main evidences for this transition are observed experimentally and confirmed theoretically: (i) strongly blue-shifted ground-state emission, accompanied by increase separation of ground and excited transition energies; and (ii) change in the orientation of the main axis of linear polarization of the photoluminescence, from parallel to perpendicular with respect to the wire axis. This latter effect, whose origin is shown to be purely due to quantum confinement and valence band mixing, sets in at wire lengths of only 30 nm.
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| 35. |
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
- Atlasov, K.A., et al.
(författare)
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Wavelength and loss splitting in directly coupled photonic-crystal defect microcavities
- 2008
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Ingår i: Optics Express. - 1094-4087. ; 16:20, s. 16255-16264
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Tidskriftsartikel (refereegranskat)abstract
- Coupling between photonic-crystal defect microcavities is observed to result in a splitting not only of the mode wavelength but also of the modal loss. It is discussed that the characteristics of the loss splitting may have an important impact on the optical energy transfer between the coupled resonators. The loss splitting - given by the imaginary part of the coupling strength - is found to arise from the difference in diffractive outof-plane radiation losses of the symmetric and the antisymmetric modes of the coupled system. An approach to control the splitting via coupling barrier engineering is presented. © 2008 Optical Society of America.
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| 43. |
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| 44. |
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| 45. |
- Gallo, P., et al.
(författare)
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Integration of site-controlled pyramidal quantum dots and photonic crystal membrane cavities
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 263101-
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Tidskriftsartikel (refereegranskat)abstract
- The authors demonstrate the deterministic coupling between a single, site-controlled InGaAs/GaAs pyramidal quantum dot (QD) and a photonic crystal membrane cavity defect. The growth of self-ordered pyramidal QDs in small (300 nm base side) tetrahedral recesses etched on (111)B GaAs substrates was developed in order to allow their integration within the thin GaAs membranes. Accurate (better than 50 nm) positioning of the QD with respect to the optical cavity mode is achieved reproducibly owing to the site control. Coupling of the dot emission with the cavity mode is evidenced in photoluminescence measurements. The deterministic positioning of the pyramidal QDs and the control of their emission spectrum opens the way for devices based on QDs integrated with coupled nanocavities.
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| 46. |
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| 47. |
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| 48. |
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| 49. |
- Karlsson, Fredrik, 1974-, et al.
(författare)
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Strongly reduced exciton transfer between parallel quantum wires
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:10, s. 101108-101108-3
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Tidskriftsartikel (refereegranskat)abstract
- Exciton transfer between two parallel GaAs V-groove quantum wires or two planar quantum wells separated by AlGaAs barriers ranging from 5.5 nm to 20 nm thickness is studied by photoluminescence and photoluminescence excitation spectroscopy. It is found that the transfer is strongly reduced between the widely spaced quantum wires as compared with quantum wells. This observation is supported by model calculations, which yield strong dimensionality dependence of the photon-exchange transfer.
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| 50. |
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