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| 2. |
- Leon, R., et al.
(författare)
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Defect states in red-emitting InxAl1-xAs quantum dots
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:8
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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.
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| 3. |
- Marcinkevicius, Saulius, et al.
(författare)
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High spectral uniformity of AlGaN with a high Al content evidenced by scanning near-field photoluminescence spectroscopy
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:24, s. 241108-
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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.
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| 4. |
- Marcinkevičius, Saulius, et al.
(författare)
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Scanning near-field optical microscopy of AlGaN epitaxial layers
- 2016
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Ingår i: UV and Higher Energy Photonics. - : SPIE - International Society for Optical Engineering. - 9781510602434 - 9781510602441
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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.
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| 5. |
- Marcinkevicius, Saulius, et al.
(författare)
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Time-resolved photoluminescence and Raman scattering of InAsSb/InP quantum dots
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:18
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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.
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| 6. |
- Ademuyiwa, Adesoji O., et al.
(författare)
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Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
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Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
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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.
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| 7. |
- Bertulis, K., et al.
(författare)
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GaBiAs : A material for optoelectronic terahertz devices
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:20
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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.
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| 8. |
- Chen, Miaoxiang, 1962-, et al.
(författare)
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1 micron wavelength photo- and electroluminescence from a conjugated polymer
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:18, s. 3570-3572
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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%.
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| 9. |
- Epifani, Mauro, et al.
(författare)
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Solvothermal Synthesis, Gas-Sensing Properties, and Solar Cell-Aided Investigation of TiO2-MoOx Nanocrystals
- 2017
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Ingår i: ChemNanoMat. - : John Wiley & Sons. - 2199-692X. ; 3:11, s. 798-807
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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.
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| 10. |
- Gaarder, A., et al.
(författare)
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Dopant distribution in selectively regrown InP : Fe studied by time-resolved photoluminescence
- 2001
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 226:4, s. 451-457
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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.
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