| 1. |
|
|
| 2. |
- Leon, R., et al.
(författare)
-
Defect states in red-emitting InxAl1-xAs quantum dots
- 2002
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:8
-
Tidskriftsartikel (refereegranskat)abstract
- Optical and transport measurements carried out in pn diodes and Schottky barriers containing multilayers of InAlAs quantum dots embedded in AlGaAs barriers show that while red emission from quantum dot (QD) states is obtained at similar to1.8 eV, defect states dominate the optical properties and transport in these quantum dots. These defects provide nonradiative recombination paths, which shortens the carrier lifetimes in QD's to tens of picoseconds (from similar to1 ns) and produce deep level transient spectroscopy (DLTS) peaks in both p and n type structures. DLTS experiments performed with short filling pulses and bias dependent measurements on InAlAs QD's on n-AlGaAs barriers showed that one of the peaks can be attributed to either QD/barrier interfacial defects or QD electron levels, while other peaks are attributed to defect states in both p and n type structures.
|
|
| 3. |
- Marcinkevicius, Saulius, et al.
(författare)
-
High spectral uniformity of AlGaN with a high Al content evidenced by scanning near-field photoluminescence spectroscopy
- 2014
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:24, s. 241108-
-
Tidskriftsartikel (refereegranskat)abstract
- Scanning near-field photoluminescence (PL) spectroscopy was applied to study spatial variations of emission spectra of AlxGa1-xN epilayers with 0.6 <= x <= 0.7. PL spectra were found to be spatially uniform with peak wavelength standard deviations of only similar to 2 meV and ratios between peak intensity standard deviations and average peak intensity values of 0.06. The observed absence of correlation between the PL peak wavelength and intensity shows that spatial distribution of nonradiative recombination centers is not related to band potential fluctuations. Our results demonstrate that the homogeneous broadening and the random cation distribution primarily determine PL line-widths for layers grown under optimized conditions.
|
|
| 4. |
- Marcinkevičius, Saulius, et al.
(författare)
-
Scanning near-field optical microscopy of AlGaN epitaxial layers
- 2016
-
Ingår i: UV and Higher Energy Photonics. - : SPIE - International Society for Optical Engineering. - 9781510602434 - 9781510602441
-
Konferensbidrag (refereegranskat)abstract
- Scanning near-field PL spectroscopy was applied to study spatial variations of the emission spectra of AlGaN epilayers with AlN molar fractions between 0.3 and 0.7. Experiments were performed at 300 K with 100 nm spatial resolution. In general, photoluminescence spectra were found to be highly uniform with the peak energy deviation of 2 to 6 meV for different alloy compositions. In the 30% and 42% Al layers, a slightly lower Al content and a higher point defect concentration at the boundaries of growth domains were detected. These features were attributed to the higher mobility of Ga adatoms during growth. The inhomogeneous broadening beyond the random alloy distribution was found negligible for the 30% and 42% Al samples, and about 40 - 50 meV for the layers with a larger Al content.
|
|
| 5. |
- Marcinkevicius, Saulius, et al.
(författare)
-
Time-resolved photoluminescence and Raman scattering of InAsSb/InP quantum dots
- 2005
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:18
-
Tidskriftsartikel (refereegranskat)abstract
- InAsSb quantum dots (QDs) grown by metalorganic vapor phase epitaxy on In0.53Ga0.47As/InP under different TMSb/AsH3 flow ratios have been characterized by means of continuous wave and time-resolved photoluminescence (PL) as well as Raman scattering. It was found that the flow ratio has a very strong influence on the QD composition, PL peak energies, and carrier recombination times. While the samples prepared using low TMSb/AsH3 flow ratios show a bimodal character with both InAs and InAsSb QDs present, in the structures grown at high flow ratios the InAsSb QDs dominate, showing strong photoluminescence intensity, fast carrier capture and slow recombination.
|
|
| 6. |
- Ademuyiwa, Adesoji O., et al.
(författare)
-
Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
-
Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
|
|
| 7. |
- Bertulis, K., et al.
(författare)
-
GaBiAs : A material for optoelectronic terahertz devices
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:20
-
Tidskriftsartikel (refereegranskat)abstract
- GaBiAs layers have been grown by molecular beam epitaxy at low (270-330 degrees C) temperatures and were characterized by several experimental techniques. It was shown that the spectral photosensitivity cutoff wavelength reaches similar to 1.4 mu m when the growth temperature is as low as 280 degrees C. Optical pump-terahertz probe measurements made on these layers have evidenced that the electron trapping time decreases with decreasing growth temperature from 20 to about 1 ps. GaBiAs layers were used for manufacturing photoconductive terahertz emitters and detectors, which, when excited with Ti:sapphire laser pulses, have demonstrated a signal bandwidth of 3 THz.
|
|
| 8. |
- Chen, Miaoxiang, 1962-, et al.
(författare)
-
1 micron wavelength photo- and electroluminescence from a conjugated polymer
- 2004
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:18, s. 3570-3572
-
Tidskriftsartikel (refereegranskat)abstract
- We report photo- and electroluminescence from an alternating conjugated polymer consisting of fluorene units and low-band gap donor-acceptor-donor (D-A-D) units. The D-A-D segment includes two electron-donating thiophene rings combined with a thiadiazolo-quinoxaline unit, which is electron withdrawing to its nature. The resulting polymer is conjugated and has a band gap of 1.27 eV. The corresponding electro- and photoluminescence spectra both peak at approximately 1 mum. Light-emitting diodes, based on a single layer of the polymer, demonstrated external quantum efficiencies from 0.03% to 0.05%.
|
|
| 9. |
- Epifani, Mauro, et al.
(författare)
-
Solvothermal Synthesis, Gas-Sensing Properties, and Solar Cell-Aided Investigation of TiO2-MoOx Nanocrystals
- 2017
-
Ingår i: ChemNanoMat. - : John Wiley & Sons. - 2199-692X. ; 3:11, s. 798-807
-
Tidskriftsartikel (refereegranskat)abstract
- Titania anatase nanocrystals were prepared by sol-gel/solvothermal synthesis in oleic acid at 250 °C, and modified by co-reaction with Mo chloroalkoxide, aimed at investigating the effects on gas-sensing properties induced by tailored nanocrystals surface modification with ultra-thin layers of MoOx species. For the lowest Mo concentration, only anatase nanocrystals were obtained, surface modified by a disordered ultra-thin layer of mainly octahedral MoVI oxide species. For larger Mo concentrations, early MoO2 phase segregation occurred. Upon heat treatment up to 500 °C, the sample with the lowest Mo concentration did not feature any Mo oxide phase segregation, and the surface Mo layer was converted to dense octahedral MoVI oxide. At larger Mo concentrations all segregated MoO2 was converted to MoO3. The two different materials typologies, depending on the Mo concentration, were used for processing gas-sensing devices and tested toward acetone and carbon monoxide, which gave a greatly enhanced response, for all Mo concentrations, to acetone (two orders of magnitude) and carbon monoxide with respect to pure TiO2. For the lowest Mo concentration, dye-sensitized solar cells were also prepared to investigate the influence of anatase surface modification on the electrical transport properties, which showed that the charge transport mainly occurred in the ultra-thin MoOx surface layer.
|
|
| 10. |
- Gaarder, A., et al.
(författare)
-
Dopant distribution in selectively regrown InP : Fe studied by time-resolved photoluminescence
- 2001
-
Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 226:4, s. 451-457
-
Tidskriftsartikel (refereegranskat)abstract
- We apply time-resolved photoluminescence with 1 mum spatial resolution for the characterization of iron distribution in semi-insulating InP:Fe epitaxial layers regrown by hydride vapor-phase epitaxy around etched mesas. The InP:Fe regrowth was carried out on InP:S mesas etched both along the [110] and [110] crystallographic directions, as well as on InP/InGaAsP in-plane lasers. In all cases, the Fe concentration was found to be close to the target values and showed little variation along the regrown layers.
|
|
| 11. |
- Leon, Rosa, et al.
(författare)
-
Dislocation-induced spatial ordering of InAs quantum dots : Effects on optical properties
- 2002
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:9, s. 5826-5830
-
Tidskriftsartikel (refereegranskat)abstract
- Misfit dislocations were used to modify the surface morphology and to attain spatial ordering of quantum dots (QDs) by molecular beam epitaxy. Effects of anneal time and temperature on strain-relaxed InxGa1-xAs/GaAs layers and subsequent spatial ordering of InAs QDs were investigated. Photoluminescence (PL) and time-resolved PL was used to study the effects of increased QD positional ordering, increased QD uniformity, and their proximity to dislocation arrays on their optical properties. Narrower inhomogeneous PL broadening from the QDs ordered on dislocation arrays were observed, and differences in PL dynamics were found.
|
|
| 12. |
- Leon, R., et al.
(författare)
-
Effects of proton irradiation on luminescence emission and carrier dynamics of self-assembled III-V quantum dots
- 2002
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 49:6, s. 2844-2851
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of proton irradiation (1.5 MeV) on photoluminescence intensities and carrier dynamics were compared between III-V quantum dots and similar quantum well structures. A significant enhancement in radiation tolerance is seen with three-dimensional (3-D) quantum confinement.. Measurements were carried out in different quantum dot (QD) structures, varying in material (InGaAs/GaAs and InAlAS/AlGaAS), QD surface density (4 x 10(8) to 3 x 10(10) cm(-2)), and substrate orientation [(100) and (311) B]. Similar trends were observed for all QD samples. A slight increase in PL emission after low to intermediate proton doses, are also observed in InGaAs/GaAs (100) QD structures. The latter is explained in terms of more efficient carrier transfer from the wetting layer via radiation-induced defects.
|
|
| 13. |
- Liuolia, Vytautas, et al.
(författare)
-
Dynamics of carrier recombination and localization in AlGaN quantum wells studied by time-resolved transmission spectroscopy
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:9
-
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.
|
|
| 14. |
- Liuolia, Vytautas, et al.
(författare)
-
Photoexcited carrier dynamics in AlInN/GaN heterostructures
- 2012
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:24, s. 242104-
-
Tidskriftsartikel (refereegranskat)abstract
- Photoexcited carrier dynamics and localization potentials in Al0.86In0.14N/GaN heterostructures have been examined by time-resolved and scanning near-field photoluminescence (PL) spectroscopy. The large GaN and AlInN PL intensity difference, and the short AlInN PL decay and GaN PL rise times indicate efficient photoexcited hole transfer from AlInN to GaN via sub-band-gap states. These states are attributed to extended defects and In clusters. Near-field PL scans show that diameter of the localization sites and the distance between them are below 100 nm. Spatial variations of the GaN PL wavelength have been assigned to the electric field inhomogeneities at the heterostructure interface.
|
|
| 15. |
- Marcinkevicius, Saulius, et al.
(författare)
-
Carrier capture and relaxation in quantum dot structures with different dot densities
- 2000
-
Ingår i: Microelectronic Engineering. - 0167-9317 .- 1873-5568. ; feb-51, s. 79-83
-
Tidskriftsartikel (refereegranskat)abstract
- Carrier dynamics has been measured by time-resolved photoluminescence in self-assembled InGaAs/GaAs quantum dot structures with dot density of the order of 10(8) to 10(10) cm(2). The time of carrier transfer into a dot, which is in the region from 2 to 20 PS, has been found to decrease with increasing quantum dot density. The temperature and photoexcited carrier density dependencies of the carrier transfer times suggest that potential barriers at the barrier, wetting layer and quantum dot interfaces hinder carrier capture in low-density quantum dot structures.
|
|
| 16. |
- Marcinkevicius, Saulius, et al.
(författare)
-
Changes in carrier dynamics induced by proton irradiation in quantum dots
- 2002
-
Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 314:04-jan, s. 203-206
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of proton irradiation on carrier dynamics were investigated by time-resolved photoluminescence on different InGaAs/GaAs quantum-dot (QD) structures varying in QD surface density and substrate orientation, as well as thin InGaAs quantum wells. The carrier lifetimes in the dots are much less affected by proton irradiation than in the wells. Decrease in lifetimes of only 40 percent at the highest proton dose are observed in some of the QDs, whereas an similar to20 to similar to40-fold decrease is observed in the wells. Similar trends were observed for all quantum dot samples.
|
|
| 17. |
- Marcinkevicius, Saulius, et al.
(författare)
-
Influence of annealing on carrier dynamics in As ion-implanted epitaxially lifted-off GaAs layers
- 2000
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:10, s. 1306-1308
-
Tidskriftsartikel (refereegranskat)abstract
- Electrical and dynamical optical characterization of As-ion implanted and annealed GaAs has been performed. Changes of physical properties induced by annealing have been studied in detail by using layers annealed in small steps in the temperature range 500-700 degrees C. The carrier trapping rate increases exponentially with increase of inverse annealing temperature indicating that in ion-implanted GaAs ultrafast carrier capture occurs to the same trapping centers as in low-temperature-grown GaAs. Relatively large resistivity and electron mobility in As-implanted GaAs have been observed after annealing, which shows that this material possesses properties required for a variety of ultrafast optoelectronic applications.
|
|
| 18. |
- Marcinkevicius, Saulius, et al.
(författare)
-
Intrinsic electric fields in AlGaN quantum wells
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:8
-
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.
|
|
| 19. |
- Marcinkevicius, Saulius, et al.
(författare)
-
Photoexcited carrier transfer in InGaAs quantum dot structures : Dependence on the dot density
- 2000
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:17, s. 2406-2408
-
Tidskriftsartikel (refereegranskat)abstract
- Carrier dynamics has been measured by time-resolved photoluminescence in self-assembled InGaAs/GaAs quantum-dot structures with dot density of the order of 10(8)-10(10) cm(-2). The time of carrier transfer into a dot, which ranges from 2 to 20 ps, has been found to decrease with increasing quantum dot density. The temperature and photoexcited carrier density dependencies of the carrier transfer times suggest that potential barriers at wetting layer and quantum-dot interfaces hinder carrier capture in low-density quantum-dot structures.
|
|
| 20. |
- Marcinkevicius, Saulius, et al.
(författare)
-
Rapid carrier relaxation by phonon emission in In0.6Ga0.4As/GaAs quantum dots
- 2001
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 6411:11
-
Tidskriftsartikel (refereegranskat)abstract
- Carrier transfer into quantum dots has been investigated by time-resolved photoluminescence spectroscopy in a set of In0.6Ga0.4As/GaAs quantum dot structures with gradually changing interband transition and intraband level energies. Quantum dot energy levels were tuned by thermal compositional disordering of the inter-face. Time-resolved photoluminescence for low photoexcited carrier densities show efficient electron relaxation by LO phonon emission for samples in which the electron energy level separation is close to the LO phonon energy. Slower carrier transfer in samples with abrupt quantum dot/barrier interfaces is also found, the latter is attributed to strain-induced or compositional potential barriers at the quantum dot inter-face.
|
|
| 21. |
- Messmer, E. R., et al.
(författare)
-
Properties of semi-insulating GaAs : Fe grown by hydride vapor phase epitaxy
- 2000
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 147:8, s. 3109-3110
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we analyze GaAs grown by hydride vapor phase epitaxy (HVPE) and doped with four different iron concentrations between 4 X 10(16) and 4.5 X 10(20) cm(-3). From temperature dependent current-voltage measurements we observed the highest resistivity in the lowest doped sample. We also quantified the activation energy. These results together with those of time resolved photoluminescence measurements indicate that in the sample with the lowest Fe concentration, EL2 may be dominant. From the analysis of the time resolved photoluminescence measurements, the intrinsic EL2 concentration and the electron and hole capture cross sections of Fe in GaAs were estimated.
|
|
| 22. |
|
|
| 23. |
- Pellegrino, P., et al.
(författare)
-
Time-resolved analysis of the white photoluminescence from SiO2 films after Si and C coimplantation
- 2004
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:1, s. 25-27
-
Tidskriftsartikel (refereegranskat)abstract
- The analysis of the white photoluminescence (PL) from Si+ and C+ coimplanted SiO2 is reported as a function of the implanted dose. By both steady and time-resolved measurements, the presence of several components in the emission between 2 and 3.3 eV has been resolved. The decays of the PL transients are characterized by short lifetimes, below 2 ns. For the emission at 2.1-2.3 eV, photoluminescence decay transients have been measured, obtaining a fast relaxation component of about 50-70 ps, followed by a slower component of the order of 1 ns. These values contrast with the very slow behavior, characteristic for the light emission from Si nanocrystals, and make carbon-related emitting centers interesting for optoelectronic applications where fast switching behavior is important.
|
|
| 24. |
- Pinos, Andrea, et al.
(författare)
-
Aging of AlGaN quantum well light emitting diode studied by scanning near-field optical spectroscopy
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:18
-
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.
|
|
| 25. |
- Pinos, Andrea, et al.
(författare)
-
Carrier lifetimes in AlGaN quantum wells : electric field and excitonic effects
- 2008
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 41:15
-
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.
|
|
| 26. |
- Pinos, Andrea, et al.
(författare)
-
Localization potentials in AlGaN epitaxial films studied by scanning near-field optical spectroscopy
- 2011
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:11
-
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.
|
|
| 27. |
- Pinos, Andrea, et al.
(författare)
-
Optical studies of degradation of AlGaN quantum well based deep ultraviolet light emitting diodes
- 2010
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108:9, s. 093113-
-
Tidskriftsartikel (refereegranskat)abstract
- Aging under high current stress of AlGaN quantum well based light emitting diodes with high and low Al content in the wells emitting at 270 nm and 335 nm, respectively, has been studied by scanning near field optical spectroscopy and far field electroluminescence, photoluminescence and time-resolved photoluminescence. In the high Al content devices emission band related to optical transitions in the cladding involving nitrogen vacancies has been found. Evolution of this band during aging suggests that the role of N vacancies is crucial in the aging process by aiding defect generation and formation of high conductivity channels.
|
|
| 28. |
- Pinos, Andrea, et al.
(författare)
-
Screening dynamics of intrinsic electric field in AlGaN quantum wells
- 2008
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:6, s. 061907-
-
Tidskriftsartikel (refereegranskat)abstract
- Shift of the transition energy after pulsed optical excitation in Al0.35Ga0.65N/Al0.49Ga0.51N quantum well (QW) structures with varying well width has been studied by time-resolved photoluminescence. The shift dynamics, which is due to descreening of the intrinsic electric field, has characteristic times similar to carrier lifetimes revealing negligible influence of trapped carriers on screening. Comparison of the experimental spectral shifts with the calculations has shown that the intrinsic field in our AlGaN QWs is about 0.4-0.5 MV/cm, which is about a factor of two smaller than the value calculated using the theoretical polarization constants.
|
|
| 29. |
- Schriber, Jeffrey R., et al.
(författare)
-
Hispanics Have the Lowest Stem Cell Transplant Utilization Rate for Autologous Hematopoietic Cell Transplantation for Multiple Myeloma in the United States : A CIBMTR Report
- 2017
-
Ingår i: Cancer. - : John Wiley & Sons. - 0008-543X .- 1097-0142. ; 123:16, s. 3141-3149
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Race/ethnicity remains an important barrier in clinical care. The authors investigated differences in the receipt of autologous hematopoietic cell transplantation (AHCT) among patients with multiple myeloma (MM) and outcomes based on race/ethnicity in the United States. METHODS: The Center for International Blood and Marrow Transplant Research database was used to identify 28,450 patients who underwent AHCT for MM from 2008 through 2014. By using data from the National Cancer Institute's Surveillance, Epidemiology, and End Results 18 registries, the incidence of MM was calculated, and a stem cell transplantation utilization rate (STUR) was derived. Post-AHCT outcomes were analyzed among patients ages 18 to 75 years who underwent melphalan-conditioned peripheral cell grafts (N = 24,102). RESULTS: The STUR increased across all groups from 2008 to 2014. The increase was substantially lower among Hispanics (range, 8.6%-16.9%) and non-Hispanic blacks (range, 12.2%-20.5%) compared with non-Hispanic whites (range, 22.6%-37.8%). There were 18,046 non-Hispanic whites, 4123 non-Hispanic blacks, and 1933 Hispanic patients. The Hispanic group was younger (P <.001). Fewer patients older than 60 years underwent transplantation among Hispanics (39%) and nonHispanic blacks (42%) compared with non-Hispanic whites (56%). A Karnofsky score <90% and a hematopoietic cell transplantation comorbidity index score >3 were more common in non-Hispanic blacks compared with Hispanic and non-Hispanic whites (P <.001). More Hispanics (57%) versus non-Hispanic blacks (54%) and non-Hispanic whites (52%; P <.001) had stage III disease. More Hispanics (48%) versus non-Hispanic blacks (45%) and non-Hispanic whites (44%) had a very good partial response or better before transplantation (P =.005). Race/ethnicity did not impact post-AHCT outcomes. CONCLUSIONS: Although the STUR increased, it remained low and was significantly lower among Hispanics followed by non-Hispanic blacks compared with non-Hispanic whites. Race/ethnicity did not impact transplantation outcomes. Efforts to increase the rates of transplantation for eligible patients who have MM, with an emphasis on groups that underuse transplantation, are warranted. (C) 2017 American Cancer Society.
|
|
| 30. |
- Siegert, Jörg, et al.
(författare)
-
Carrier recombination in aligned InAs/GaAs quantum dots grown in strain-relaxed InGaAs layers
- 2003
-
Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 0:4, s. 1213-
-
Tidskriftsartikel (refereegranskat)abstract
- Alignment of InAs quantum dots was achieved by introducing misfit dislocations in a metastable InGaAs layer and subsequent annealing. Photoexcited carrier dynamics were studied using time-resolved photoluminescence. Comparison with control “non-aligned” InAs quantum dots show remarkable differences in integrated photoluminescence intensities with excitation power and photoluminescence decay time dependences on excitation intensities. Low-temperature carrier lifetimes were found to be below one hundred picoseconds for the aligned quantum dots and to be determined by non-radiative recombination processes. Samples with different barrier thicknesses between the InGaAs and the quantum dot layer allow the discussion of possible influences of carrier traps at InGaAs/GaAs interface and in the dot layer.
|
|
| 31. |
- Siegert, Jörg, et al.
(författare)
-
Photoexcited carrier dynamics in aligned InAs/GaAs quantum dots grown on strain-relaxed InGaAs layers
- 2003
-
Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 18:4, s. 541-
-
Tidskriftsartikel (refereegranskat)abstract
- Carrier dynamics in aligned InAs/GaAs quantum dots (QDs) grown on cross-batched patterns induced by metastable InxGa1-xAs layers have been studied by time-resolved photoluminescence. The low-temperature carrier lifetimes were found to be of the order of 100-200 ps and determined by carrier trapping and nonradiative recombination. Comparisons with control "nonaligned" InAs QDs show remarkable differences in dependence of peak PL intensities on excitation power, and in PL decay times dependences on both temperature and excitation intensities. Possible origin of traps, which determine the carrier lifetimes, is discussed.
|
|
| 32. |
- Suomalainen, S., et al.
(författare)
-
Semiconductor saturable absorbers with recovery time controlled by lattice mismatch and band-gap engineering
- 2008
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5107 .- 1873-4944. ; 147:2-3, s. 156-160
-
Tidskriftsartikel (refereegranskat)abstract
- The recovery time of absorption in semiconductor quantum-well structures is one of the key parameters that determines the performance of pulsed lasers mode-locked or Q-switched by semiconductor saturable absorbers. In this paper we discuss new methods to control the recovery time of absorption. The first method is based on controlling the crystalline quality of the absorbing material and thus the density of non-radiative recombination centers that are responsible for the fast recovery of the absorption. With this technique, we were able to fabricate semiconductor saturable absorber mirrors (SESAMs) with recovery times of about 4.5 ps at 1 mu m and 40 ps at 1.55 mu m. Another approach that we propose and demonstrate in this paper is based on band-gap engineering that enables short recovery times to be achieved through fast relaxation of excited photocarriers via intraband scattering. A 24 ps carrier decay time was achieved by placing deep quantum-wells next to the shallow quantum-wells responsible for the nonlinear absorption. We demonstrated that the recovery time can be changed by modifying the thickness of the deep and shallow quantum-wells.
|
|
| 33. |
|
|
| 34. |
- Zurauskiene, N., et al.
(författare)
-
Optically detected microwave resonance and carrier dynamics in InAs/GaAs quantum dots
- 2005
-
Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 107:2, s. 435-439
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of small-sized high density InAs/GaAs quantum dots (emitting at 1.25 eV) are studied by means of optically detected microwave resonance spectroscopy and time resolved photoluminescence techniques. The results are discussed in terms of trapping and thermal escape of the carriers as well as their relaxation and recombination in quantum dots. The data are compared with those recently obtained on shallowly formed InAs quantum dot structures.
|
|
| 35. |
- Zurauskiene, N., et al.
(författare)
-
Semiconductor nanostructures for infrared applications
- 2004
-
Ingår i: Functional Nanomaterials For Optoelectronics And Other Applications. - : Trans Tech Publications Inc.. ; , s. 99-108
-
Konferensbidrag (refereegranskat)abstract
- The results of time-resolved photo luminescence (TRPL) and optically detected microwave resonance (ODMR) spectroscopy investigations of semiconductor quantum dots and quantum wells are presented. The ODMR spectra of InAs/GaAs QDs were detected via modulation of the total intensity of the QDs emission induced by 95 GHz microwave excitation and the exciton fine structure was studied. Very long life times (up to 10 ns) of photoexcited carriers were observed in this system using TRPL at low temperatures and excitation intensities promising higher responsitivity of such QDs for infrared photodetector development. The effects of proton and alpha particles irradiation on carrier dynamics were investigated on different InGaAs/GaAs, InAlAs/AlGaAs and GaAs/AlGaAs QD and QW systems. The results showed that carrier lifetimes in QDs are much less affected by proton irradiation than that in QWs. A strong influence of irradiation on PL intensity was observed in multiple QWs after high-energy alpha particles irradiation.
|
|
