| 1. |
- Lim, W., et al.
(author)
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Migration and Luminescence Enhancement Effects of Deuterium in ZnO/ZnCdO Quantum Wells
- 2008
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 032103-
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Journal article (peer-reviewed)abstract
- ZnO/ZnCdO/ZnO multiple quantum well samples grown on sapphire substrates by molecular beam epitaxy and annealed in situ were exposed to D2 plasmas at 150 °C. The deuterium showed migration depths of ~0.8 µm for 30 min plasma exposures, with accumulation of 2H in the ZnCdO wells. The photoluminescence (PL) intensity from the samples was increased by factors of 5 at 5 K and ~20 at 300 K as a result of the deuteration, most likely due to passivation of competing nonradiative centers. Annealing up to 300 °C led to increased migration of 2H toward the substrate but no loss of deuterium from the sample and little change in the PL intensity. The initial PL intensities were restored by annealing at >=400 °C as 2H was evolved from the sample (~90% loss by 500 °C). By contrast, samples without in situ annealing showed a decrease in PL intensity with deuteration. This suggests that even moderate annealing temperatures lead to degradation of ZnCdO quantum wells.
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| 2. |
- Donchev, V., et al.
(author)
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Enhancement of the photoluminescence intensity of a single InAs/GaAs quantum dot by separate generation of electrons and holes
- 2006
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In: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 48:10, s. 1993-1999
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Journal article (peer-reviewed)abstract
- It is demonstrated that the microphotoluminescence (µPL) spectrum of a single InAs/GaAs self-assembled quantum dot (QD) undergoes considerable changes when the primary laser excitation is complemented with an additional infrared laser. The primary laser, tuned slightly below the GaAs band gap, provides electron-hole pairs in the wetting layer (WL), as well as excess free electrons from ionized shallow acceptors in the GaAs barriers. An additional IR laser with a fixed energy well below the QD ground state transition generates excess free holes from deep levels in GaAs. The excess electron and hole will experience diffusion separately, due to the time separation between the two events of their generation, to eventually become captured into the QD. Although the generation rates of excess carries are much lower than that of the electron-hole pair generation in the WL, they considerably influence the QD emission at low temperatures. The integrated PL intensity increases by several times as compared to single-laser excitation, and the QD exciton spectrum is redistributed in favor of a more neutral charge configuration. The dependence of the observed phenomenon on the powers of the two lasers and the temperature has been studied and is consistent with the model proposed. The concept of dual excitation could be successfully applied to different low-dimensional semiconductor structures in order to manipulate their charge state and emission intensity. © Nauka/Interperiodica 2006.
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| 3. |
- Moskalenko, Evgenii, 2000-, et al.
(author)
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Effect of an additional infrared excitation on the luminescence efficiency of a single InAs/GaAs quantum dot
- 2003
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:15, s. 1553171-15531714
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Journal article (peer-reviewed)abstract
- Microphotoluminescence (PL) spectra of a single InAs/GaAs self-assembled quantum dot (QD) are studied under the main excitation of electron-hole pairs in the wetting layer (WL) and an additional infrared (IR) laser illumination. It is demonstrated that the IR laser with fixed photon energy well below the QD ground state induces striking changes in the spectra for a range of excitation energies and powers of the two lasers. For the main excitation above a threshold energy, defined as the onset of transitions between shallow acceptors and the conduction band in GaAs, the addition of the IR laser will induce a considerable increase in the QD emission intensity. This is explained in terms of additional generation of extra electrons and holes into the QD by the two lasers. For excitation below the threshold energy, the carrier capture efficiency from the WL into the QD is suggested to be essentially determined by the internal electric-field-driven carrier transport in the plane of the WL. The extra holes, generated in the GaAs by the IR laser, are supposed to effectively screen the built-in field, which results in a considerable reduction of the carrier collection efficiency into the QD and, consequently, a decrease of the QD PL intensity. A model is presented which allows estimating the magnitude of the built-in field as well as the dependence of the observed increase of the QD PL intensity on the powers of the two lasers. The use of an additional IR laser is considered to be helpful to effectively manipulate the emission efficiency of the quantum dot, which could be used in practice in quantum-dot-based optical switches.
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| 4. |
- Moskalenko, Evgenii, et al.
(author)
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Effect of an electric field on the carrier collection efficiency of InAs quantum dots
- 2005
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In: Physics of the solid state. - : Pleiades Publishing Ltd. - 1063-7834 .- 1090-6460. ; 47:11, s. 2154-2161
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Journal article (peer-reviewed)abstract
- Individual and multiquantum dots of InAs are studied by means of microphotoluminescence in the case where, in addition to the principal laser exciting photoluminescence, second infrared laser is used. It is demonstrated that the absorption of the infrared photons effectively creates free holes in the sample, which leads to both a change in the charge state of a quantum dot and to a considerable reduction of their photoluminescence signal. The latter effect is explained in terms of effective screening of the internal electric field, facilitating carrier transport along the plane of a wetting layer, by the surplus holes from the infrared laser. It is shown that the effect of quenching of quantum dot photoluminescence gradually disappears at increased sample temperature (T) and/or dot density. This fact is due to the essentially increased value of quantum dot collection efficiency, which could be achieved at elevated sample temperatures for individual quantum dots or even at low T for the case of multiquantum dots. It is suggested that the observed phenomena can be widely used in practice to effectively manipulate the collection efficiency and the charge state of quantum-dot-based optical devices. © 2005 Pleiades Publishing, Inc.
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| 5. |
- Moskalenko, Evgenii, et al.
(author)
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Effects of separate carrier generation on the emission properties of InAs/GaAs quantum dots
- 2005
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In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 5:11, s. 2117-2122
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Journal article (peer-reviewed)abstract
- Individual quantum dots have been studied by means of microphotoluminescence with dual-laser excitation. The additional infrared laser influences the dot charge configuration and increases the dot luminescence intensity. This is explained in terms of separate generation of excess electrons and holes into the dot from the two lasers. With increasing dot density and/or sample temperature, the increase of the luminescence intensity vanishes progressively, while the possibility to control the dot charge remains. © 2005 American Chemical Society.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Moskalenko, Evgenii, 2000-, et al.
(author)
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The effect of an additional infrared laser on the carrier collection efficiency of InAs quantum dots
- 2004
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:24, s. 4896-4898
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Journal article (peer-reviewed)abstract
- The impact of single and multi-quantum dots (QD) on the exposure by a low-energy laser was investigated using micro-photoluminescence. The presence of the low-energy laser effectively quenched the single QD luminescence, at low temperatures. An induced screening of a built-in electric field that played an important role as a carrier capture mechanism led to this effect. When the capture efficieny was increased by elevated crystal temperature, the influence of the low-energy laser decreased.
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| 12. |
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| 13. |
- Holtz, Per-Olof, 1951-, et al.
(author)
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Effects of External Fields on the Excitonic Emission from Single InAs/GaAs Quantum Dots
- 2008
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In: Microelectronics Journal, Vol. 39. - Microelectronics Journal : Elsevier. ; , s. 331-334
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Conference paper (peer-reviewed)abstract
- A low-temperature micro-photoluminescence (μ-PL) investigation of InAs/GaAs quantum dots (QDs) exposed to a lateral external electric field is reported. It is demonstrated that the QDs PL signal could be increased several times by altering the external and/or the internal electric field. The internal field in the vicinity of the dots could be altered by means of an additional infra-red laser. We propose a model, which is based on an essentially faster lateral transport of the charge carriers achieved in an external electric field. Consequently, also the capture probability into the dots and subsequently the dot luminescence is also enhanced. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity measured in our experiment.
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| 14. |
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| 15. |
- Holtz, Per-Olof, 1951-, et al.
(author)
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Enhanced Luminescence from InAs/GaAs Quantum Dots
- 2006
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In: Optical Materials in Defence Systems Technology III,2006. - Proceedings of SPIE 6401 : SPIE Digital Library. ; , s. 64010I-
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Conference paper (peer-reviewed)
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| 16. |
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Karlsson, Fredrik, 1974-, et al.
(author)
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Carrier diffusion in the barrier enabling formation of charged excitons in InAs/GaAs quantum dots
- 2001
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In: XXX International School on the Physics of Semiconducting Compounds,2001. - : Polish Academy of Sciences, Institute of Physics. ; , s. 387-395
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Conference paper (peer-reviewed)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the experimental conditions, such as excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusion of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots. This is proposed as a new tool to populate quantum dots with extra electrons in order to study phenomena involving charged excitons.
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| 21. |
- Karlsson, Fredrik, 1974-, et al.
(author)
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Effective tuning of the charge-state of single In(Ga)As/GaAs quantum dots by below barrier band gap excitation
- 2003
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In: Surface Science. - 0039-6028 .- 1879-2758. ; 532-535, s. 843-847
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Journal article (peer-reviewed)abstract
- The existence of a well-defined threshold energy, crucial for the charging of quantum dots (QDs), positioned between the barrier band gap and the wetting layer ground state is demonstrated. Optical excitation with energies above this threshold populates the QDs with extra electrons. The origin of the threshold is discussed in terms of acceptors in the GaAs barrier. ⌐ 2003 Elsevier Science B.V. All rights reserved.
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| 22. |
- Karlsson, Fredrik, 1974-, et al.
(author)
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Optical charging of self-assembled InAs/GaAs quantum dots
- 2002
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In: Physica scripta. T. - 0281-1847. ; 101, s. 140-142
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Journal article (peer-reviewed)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the experimental conditions, such as excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusion of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots. This is proposed as an effective tool to populate single quantum dots with extra electrons, by purely optical means, in order to study phenomena involving charged excitons.
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| 23. |
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| 24. |
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| 25. |
- Karlsson, Fredrik, 1974-, et al.
(author)
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Temperature influence on optical charging of self-assembled InAs/GaAs semiconductor quantum dots
- 2001
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:19, s. 2952-2954
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Journal article (peer-reviewed)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled InAs/GaAs quantum dots are very sensitive to excitation energy and crystal temperature. This is qualitatively explained in terms of the effective diffusivity of photogenerated particles, which affects the capture probability of the quantum dot. As a consequence, this opens the possibility of controlling the average number of excess electrons in the quantum dot by optical means. This technique may be used as a simple tool to create and study charged exciton complexes without any specially fabricated samples. ⌐ 2001 American Institute of Physics.
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| 26. |
- Karlsson, Fredrik, 1974-, et al.
(author)
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The influence of carrier diffusion on the formation of charged excitons in InAs/GaAs quantum dots
- 2002
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In: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 13:2-4, s. 101-104
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Journal article (peer-reviewed)abstract
- It is demonstrated that the photoluminescence spectra of single self-assembled quantum dots are very sensitive to the excitation energy and crystal temperature. A qualitative explanation is given in terms of the effective diffusivity of the photogenerated carriers, determined by the experimental conditions, which influence the capture probability and hence also the charge state of the quantum dots (QDs). This is proposed as an effective tool to populate quantum dots with extra electrons in order to study phenomena involving charged excitons. ⌐ 2002 Elsevier Science B.V. All rights reserved.
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| 27. |
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| 28. |
- Larsson, Mats, et al.
(author)
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Magnetic field effects on optical and transport properties in InAs/GaAs quantum dots
- 2006
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In: Physical Review B. - 1098-0121. ; 74:24
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Journal article (peer-reviewed)abstract
- A photoluminescence study of self-assembled InAs/GaAs quantum dots under the influence of magnetic fields perpendicular and parallel to the dot layer is presented. At low temperatures, the magnetic field perpendicular to the dot layer alters the in-plane transport properties due to localization of carriers in wetting layer (WL) potential fluctuations. Decreased transport in the WL results in a reduced capture into the quantum dots and consequently a weakened dot-related emission. The effect of the magnetic field exhibits a considerable dot density dependence, which confirms the correlation to the in-plane transport properties. An interesting effect is observed at temperatures above approximately 100 K, for which magnetic fields, both perpendicular and parallel to the dot layer, induced an increment of the quantum dot photoluminescence. This effect is ascribed to the magnetic confinement of the exciton wave function, which increases the probability for carrier capture and localization in the dot, but affects also the radiative recombination with a reduced radiative lifetime in the dots under magnetic compression.
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| 29. |
- Moskalenko, Evgenii, 2000-, et al.
(author)
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Acceptor-induced threshold energy for the optical charging of InAs single quantum dots
- 2002
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:19, s. 1953321-19533211
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Journal article (peer-reviewed)abstract
- We study the photoluminescence of single InAs/GaAs self-assembled quantum dots for a range of excitation powers, excitation energies and sample temperatures 4 K30 K), this effect vanishes due to the essential decrease of the steady-state free electron concentration in the GaAs barrier as a result of thermally excited free holes appearing in the GaAs barrier valence band which provides an effective recombination channel for the free electrons. These experimental observations could be used as an effective tool to create and study charged excitons in quantum dots.
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| 30. |
- Moskalenko, Evgenii, et al.
(author)
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Carrier transport in self-organized InAs/GaAs quantum-dot structures studied by single-dot spectroscopy
- 2006
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In: Physical Review B. - 1098-0121. ; 73:15
-
Journal article (peer-reviewed)abstract
- A microphotoluminescence study of single InAs/GaAs quantum dots subjected to a lateral external electric field gives insight into carrier transport and capture processes into Stranski-Krastanov-grown quantum dots. The results obtained on the excitons in a single dot demonstrate a considerable luminescence intensity enhancement of the dot as well as a charge redistribution when an electric field is applied. The charge reconfiguration is evidenced by the transition from a predominantly negatively charged to a neutral charge state of the exciton. The model proposed to explain the charge redistribution is based on an effective hole localization at the potential fluctuations of the wetting layer.
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| 31. |
- Moskalenko, Evgenii, et al.
(author)
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Effective tuning of the charge state of a single InAs/GaAs quantum dot by an external magnetic field
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:7, s. 075306-
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Journal article (peer-reviewed)abstract
- A microphotoluminescence study of single InAs/GaAs quantum dots (QDs) in the presence of an applied external magnetic field is presented. Attention is focused on the redistribution between the spectral lines of a single QD observed at increasing magnetic field parallel to the growth direction (Faraday geometry). The redistribution effect is explained by considering the electron drift velocity in the QD plane that affects the probability for capture into the QD. In contrast, no redistribution is observed when applying the magnetic field perpendicular to the growth direction (Voigt geometry).
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| 32. |
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| 33. |
- Moskalenko, Evgenii, 2000-, et al.
(author)
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Enhancement of the luminescence intensity of InAs/GaAs quantum dots induced by an external electric field
- 2007
-
In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 7:1, s. 188-193
-
Journal article (peer-reviewed)abstract
- InAs/GaAs quantum dots have been subjected to a lateral external electric field in low-temperature microphotoluminescence measurements. It is demonstrated that the dot PL signal could be increased several times depending on the magnitude of the external field and the strength of the internal (built-in) electric field, which could be altered by an additional infrared illumination of the sample. The observed effects are explained by a model that accounts for the essentially faster lateral transport of the photoexcited carriers achieved in an electric field. © 2007 American Chemical Society.
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| 34. |
- Moskalenko, Evgenii, 2000-, et al.
(author)
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Formation of the charged exciton complexes in self-assembled InAs single quantum dots
- 2002
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:11, s. 6787-6793
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Journal article (peer-reviewed)abstract
- The low-temperature photoluminescence (PL) of the self-assembled InAs single quantum dots (QD) was studied using micro-PL setup. It was demonstrated that two emission lines down shifted in energy with respect to the ground state exciton PL line appeared in the PL spectrum. The PL intensity of these lines showed a periodic behavior with the excitation energy.
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| 35. |
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| 36. |
- Moskalenko, Evgenii, et al.
(author)
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Single InAs/GaAs quantum dot spectroscopy in a lateral electric field
-
Other publication (other academic/artistic)abstract
- We report on the comprehensive study of InAs/GaAs single quantum dots subjected to a lateral external electric field by means of micro-photoluminescence (μ-PL) technique. The results obtained on the exciton in the μ-PL spectra of a single dot demonstrate a considerable PL intensity enhancement (up to a factor of 4) of the dot as well as a redistribution of the excitonic lines when an electric field is applied. The latter fact exhibits an effective charge reconfiguration of the dot from a purely negatively charged to a neutral state. The model proposed to explain the charge redistribution is based on an effective hole localization at the potential fluctuations of the wetting layer at low temperature and bias.
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| 37. |
- Moskalenko, Evgenii, 2000-, et al.
(author)
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The effect of the external lateral electric field on the luminescence intensity of InAs/GaAs quantum dots
- 2007
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In: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 49:10, s. 1995-1998
-
Journal article (peer-reviewed)abstract
- We report on low-temperature microphotoluminescence (μ-PL) measurements of InAs/GaAs quantum dots (QDs) exposed to a lateral external electric field. It is demonstrated that the QDs’ PL signal could be increased severalfold by altering the external and/or the internal electric field, which could be changed by an additional infrared laser. A model which accounts for a substantially faster lateral transport of the photoexcited carriers achieved in an external electric field is employed to explain the observed effects. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity measured in our experiment—a finding which could be used to tailor the properties of QD-based optoelectronic applications.
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| 38. |
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| 39. |
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| 40. |
- Paskov, Plamen, et al.
(author)
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Auger processes in InAs self-assembled quantum dots
- 2000
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In: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 6:1, s. 440-443
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Journal article (peer-reviewed)abstract
- An experimental evidence of Auger-like excitation processes in InAs/GaAs quantum dots is demonstrated. Photoluminescence spectra of resonantly excited dots exhibit a rich satellite structure below the ground-state emission band. The energy position and the intensity distribution of the satellites are analyzed and an interpretation of the satellites as due to shake-up processes of the interacting careers in the higher quantum dot states is suggested.
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| 41. |
- Paskov, Plamen, et al.
(author)
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Magnetoluminescence of highly excited InAs/GaAs self-assembled quantum dots
- 2000
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:11, s. 7344-7349
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Journal article (peer-reviewed)abstract
- We present magnetoluminescence measurements of InAs/GaAs self-assembled quantum dots (QD's) at different excitation intensities. By applying high excitation intensities, the magnetic field evolution of the excited-state emission of QD's is revealed. A splitting of the states with a nonzero magnetic momentum is observed and the in-plane reduced electron-hole mass is determined. The experimental value is found to be in a good agreement with the theoretical predictions based on the eight-band k·p model including both strain effect and band nonparabolicity. The density dependence of the diamagnetic shift of the ground-state emission is also studied providing evidence for screening of the Coulomb interaction in QD's.
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| 42. |
- Paskov, Plamen, 1959-, et al.
(author)
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Optical up-conversion processes in InAs quantum dots
- 2000
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In: the 25th International Conference on the Physics of Semiconductors ICPS-25,2000. ; , s. 2080-2083
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Conference paper (peer-reviewed)abstract
- Up-converted photoluminescence (UPL) in InAs/GaAs self-assembled quantum dots (QDs) is reported. With a resonant excitation of QDs we observe an efficient emission from the GaAs barrier. The excitation spectrum of the UPL shows that the signal disappears if the excitation energy is tuned below the absorption band of the QDs. The intensity of UPL exhibits an almost quadratic dependence on the excitation intensity. The observed effect is explained by a two-step two-photon absorption process involving quantum dot states as intermediate states.
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| 43. |
- Paskov, Plamen, 1959-, et al.
(author)
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Optical up-conversion processes in InAs quantum dots
- 2001
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In: Japanese Journal of Applied Physics. - 0021-4922 .- 1347-4065. ; 40:3 B, s. 2080-2083
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Journal article (peer-reviewed)abstract
- Up-converted photoluminescence (UPL) in InAs/GaAs self-assembled quantum dots (QDs) is reported. With a resonant excitation of QDs we observe an efficient emission from the GaAs barrier. The excitation spectrum of the UPL shows that the signal disappears if the excitation energy is tuned below the absorption band of the QDs. The intensity of UPL exhibits an almost quadratic dependence on the excitation intensity. The observed effect is explained by a two-step two-photon absorption process involving quantum dot states as intermediate states. ⌐ 2001 The Japan Society of Applied Physics.
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