| 1. |
- Aggerstam, Thomas, et al.
(författare)
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Electron and hole capture cross-sections of Fe acceptors in GaN:Fe epitaxially grown on sapphire
- 2007
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 36:12, s. 1621-1624
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Tidskriftsartikel (refereegranskat)abstract
- Carrier trapping of Fe (3+)/Fe2+ deep acceptors in epitaxially grown GaN:Fe on sapphire was studied by time-resolved photoluminescence. For the investigated Fe doping levels on the order of 10(18) cm(-3), the luminescence decay times are strongly dependent on the Fe concentration, indicating that Fe centers act as predominant nonradiative recombination channels. Linear dependence of the decay time on the iron concentration allows estimation of the electron capture cross-section for the Fe3+ ions, which is equal to 1.9 x 10(-15) cm(2). The upper bound for the cross-section of the hole capture of Fe2+ was evaluated as 10 x 10(-15) cm
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| 2. |
- Dong, Lin, et al.
(författare)
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Measurement of radiative lifetime in CdSe/CdS core/shell structured quantum dots
- 2009
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Ingår i: 2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009. - Washington, D.C. : OSA. - 9781557528773 ; , s. 5377385-
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Konferensbidrag (refereegranskat)abstract
- Radiative lifetime of chemically synthesized colloidal CdSe/CdS core/shell quantum dots is measured. Influence of the core size on the electron-hole pair separation is analyzed. A long radiative lifetime and the existence of electron-hole pair separation suggest high potential of these dots as gain material to achieve lasing under continuous-wave excitation.
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| 3. |
- Gautier, S., et al.
(författare)
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AlGaN/AlN multiple quantum wells grown by MOVPE on AlN templates using nitrogen as a carrier gas
- 2008
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 310:23, s. 4927-4931
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Tidskriftsartikel (refereegranskat)abstract
- AlxGa1-xN/AlN multiple quantum wells (MQWs) structures were grown by metalorganic vapour phase epitaxy (MOVPE) on pseudo AlN substrates using nitrogen as a carrier gas. Results of X-ray diffraction (XRD) and reciprocal space mapping (RSM) indicated no sign of strain relaxation in the quantum wells with respect to the AlN substrate. The MQW parameters such as thicknesses, growth rates and material compositions were extracted from XRD measurements and demonstrated an agreement with our growth conditions. No indication of parasitic reactions between ammonia and trimethyl-aluminium (TMAI) was detected in our growth process. Optical measurements revealed well-defined photoluminescence peaks at 288 and 280 nm, which are in a good agreement with the transmission experimental data. The piezoelectric field value in the Studied structures was estimated to be 900kV/cm.
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| 4. |
- Liuolia, Vytautas, et al.
(författare)
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Carrier localization in m-plane InGaN/GaN quantum wells probed by scanning near field optical spectroscopy
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:15, s. 151106-
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Tidskriftsartikel (refereegranskat)abstract
- Scanning near field optical microscopy (SNOM) was applied to study the carrier localization in single InGaN/GaN quantum well structures grown on nonpolar m-plane GaN substrates. Dual localization potential consisting of hundreds of nanometers- to micrometer-size areas as well as smaller localization centers were identified from the SNOM scans and near field photoluminescence spectral widths. The localization areas were found to align along the [0001] direction, which was attributed to partial strain relaxation at the monolayer steps. (C) 2010 American Institute of Physics. [doi:10.1063/1.3502482]
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| 5. |
- Liuolia, Vytautas, et al.
(författare)
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Dynamics of carrier recombination and localization in AlGaN quantum wells studied by time-resolved transmission spectroscopy
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:9
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved transmission and photoluminescence measurements were performed on Al0.35Ga0.65N/Al0.49Ga0.51N quantum well structures with different well widths. Comparison of transmission and luminescence data shows that dynamics of electrons and holes excited into extended quantum well states are governed by nonradiative recombination. For excitation into potential minima formed by band gap fluctuations, localization of electrons was observed. Excitation energy dependence of the pump-probe transient shape allows estimating localization potential, which is about 80 meV independently of the well width, and is probably caused by fluctuations of AlN molar fraction.
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| 6. |
- Marcinkevicius, Saulius, et al.
(författare)
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Intrinsic electric fields in AlGaN quantum wells
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:8
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsic electric fields in AlxGa1-xN/AlyGa1-yN quantum wells embedded into p-i-n structures are studied using photoluminescence experiments. Spectral shifts induced by external bias and screening by photoexcited carriers allow evaluating the intrinsic fields caused by piezoelectric and spontaneous polarizations. In quantum wells with low Al content, the field is about 1 MV/cm, which is in agreement with theoretical estimations. For high Al molar fractions (35% well, 50% barrier), the extracted intrinsic field is lower and, most importantly, has the opposite sign to that predicted by the theory.
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| 7. |
- Pinos, Andrea, et al.
(författare)
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Aging of AlGaN quantum well light emitting diode studied by scanning near-field optical spectroscopy
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:18
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Tidskriftsartikel (refereegranskat)abstract
- Emission from a 285 nm AlGaN quantum well light emitting diode has been studied by scanning near-field optical spectroscopy. The scans revealed micrometer-size domainlike areas emitting with a higher intensity and at a longer wavelength; presumably, because of a lower AlN molar fraction in these regions. Experiments performed on different days have shown that with time, intensity from these spots increases and emission wavelength shifts to the red, indicating a further change in the quantum well alloy composition. This has allowed distinguishing an aging mechanism that involves locally increased current, heating, and atom migration.
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| 8. |
- Pinos, Andrea, et al.
(författare)
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Carrier lifetimes in AlGaN quantum wells : electric field and excitonic effects
- 2008
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 41:15
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Tidskriftsartikel (refereegranskat)abstract
- Photoexcited carrier dynamics in a 280 nm AlGaN quantum well (QW) light emitting diode has been studied by time-resolved photoluminescence at forward and reverse bias. Long ( for AlGaN QWs with high Al content) room temperature carrier lifetimes of about 600 ps were measured with only a slight dependence on bias. These lifetimes are much longer than calculated free carrier tunnelling and thermionic emission times, pointing out the importance of excitonic effects for carrier dynamics in AlGaN QWs.
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| 9. |
- Pinos, Andrea, et al.
(författare)
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High current-induced degradation of AlGaN ultraviolet light emitting diodes
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:10, s. 103108-
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Tidskriftsartikel (refereegranskat)abstract
- Degradation under high current stress of AlGaN quantum well based light emitting diodes emitting at 285 and 310 nm has been studied using electroluminescence, time-resolved photoluminescence and current-voltage experimental techniques. The measurements have revealed that during aging decrease of the emission intensity is accompanied by increase of the tunneling current, increase of the nitrogen vacancy concentration and partial compensation of the p-doping. The main role in the device degradation has been ascribed to formation of tunneling conductivity channels, probably, via activation of the closed core screw dislocations with the help of nitrogen vacancies. Carrier lifetimes in the quantum wells and the p-cladding were found to be unaffected by the aging process, suggesting that the nonradiative recombination has a lesser influence on the device degradation.
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| 10. |
- Pinos, Andrea, et al.
(författare)
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Localization potentials in AlGaN epitaxial films studied by scanning near-field optical spectroscopy
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:11
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Tidskriftsartikel (refereegranskat)abstract
- Scanning near-field photoluminescence spectroscopy has been applied to evaluate bandgap fluctuations in epitaxial AlGaN films with the AlN molar fraction varying from 0.30 to 0.50. A dual localization pattern has been observed. The potential of the small-scale (<100 nm) localization, evaluated from the width of the photoluminescence spectra, is between 0 and 51 meV and increases with increased Al content. These potential variations have been assigned to small-scale compositional fluctuations occurring due to stress variations, dislocations, and formation of Al-rich grains during growth. Larger area potential variations of 25-40 meV, most clearly observed in the lower Al-content samples, have been attributed to Ga-rich regions close to grain boundaries or atomic layer steps. The density, size, and bandgap energy of these domains were found to be composition dependent. The lower bandgap domains were found to be strongly correlated with the regions with efficient nonradiative recombination.
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