| 1. |
- Toropov, A. A., et al.
(författare)
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AlGaN Nanostructures with Extremely High Room-Temperature Internal Quantum Efficiency of Emission Below 300 nm
- 2017
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Ingår i: Journal of Electronic Materials. - : SPRINGER. - 0361-5235 .- 1543-186X. ; 46:7, s. 3888-3893
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Tidskriftsartikel (refereegranskat)abstract
- We present theoretical optimization of the design of a quantum well (QW) heterostructure based on AlGaN alloys, aimed at achievement of the maximum possible internal quantum efficiency of emission in the mid-ultraviolet spectral range below 300 nm at room temperature. A sample with optimized parameters was fabricated by plasma-assisted molecular beam epitaxy using the submonolayer digital alloying technique for QW formation. High-angle annular dark-field scanning transmission electron microscopy confirmed strong compositional disordering of the thus-fabricated QW, which presumably facilitates lateral localization of charge carriers in the QW plane. Stress evolution in the heterostructure was monitored in real time during growth using a multibeam optical stress sensor intended for measurements of substrate curvature. Time-resolved photoluminescence spectroscopy confirmed that radiative recombination in the fabricated sample dominated in the whole temperature range up to 300 K. This leads to record weak temperature-induced quenching of the QW emission intensity, which at 300 K does not exceed 20% of the low-temperature value.
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| 2. |
- Shevchenko, E. A., et al.
(författare)
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AlGaN Quantum Well Heterostructures for Mid-Ultraviolet Emitters with Improved Room Temperature Quantum Efficiency
- 2014
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Ingår i: Acta Physica Polonica. A. - : POLISH ACAD SCIENCES INST PHYSICS. - 0587-4246 .- 1898-794X. ; 126:5, s. 1140-1142
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Tidskriftsartikel (refereegranskat)abstract
- We report on optical studies of exciton localization and recombination kinetics in two single 2.2 nm thick AlxGa1-xN/Alx+0.1Ga0.9-xN quantum well structures (x = 0.55 and 0.6) grown by plasma assisted molecular beam epitaxy on a c-sapphire substrate. Strong localization potential inherent for both the quantum well and barrier regions results in merging of the quantum well and barrier emission spectra into a single broad line centered at 285 nm (x = 0.55) and 275 nm (x = 0.6). Time-resolved photoluminescence measurements revealed surprising temperature stability of the photoluminescence decay time constant (approximate to 400 ps) relevant to the recombination of the quantum well localized excitons. This observation implies nearly constant quantum efficiency of the quantum well emission in the whole range from 4.6 to 300 K.
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| 3. |
- Toropov, A. A., et al.
(författare)
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AlGaN nanostructures with extremely high quantum yield at 300 K
- 2016
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Ingår i: Physics of the solid state. - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 1063-7834 .- 1090-6460. ; 58:11, s. 2261-2266
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical optimization of a quantum well heterostructure based on AlGaN solid solutions is implemented in order to attain the maximum charge carrier activation energy and the maximum exciton binding energy at a radiation wavelength of similar to 300 nm. An optimized structure sample with the radiative recombination dominating over the temperature range of 5 to 300 K and the room temperature internal quantum yield as high as 80% of the value measured at 5 K has been manufactured via plasma-assisted molecular beam epitaxy.
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| 4. |
- Toropov, A. A., et al.
(författare)
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Exciton recombination in spontaneously formed and artificial quantum wells AlxGa1-xN/AlyGa1-yN (x < y similar to 0.8)
- 2016
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Ingår i: PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 13 NO 5-6. - : WILEY-V C H VERLAG GMBH. ; , s. 232-238
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Konferensbidrag (refereegranskat)abstract
- We report on photoluminescence (PL) spectroscopy and electron microscopy studies of an AlGaN quantum well (QW) structure grown by molecular beam epitaxy under metal-rich conditions with substrate rotation. Both techniques reveal unintentional formation within the AlGaN barriers of a quasiperiodic structure of thin Ga-rich layers, whose period is controlled by both the substrate rotation rate and the AlGaN growth rate. These compositional modulations act as 1-3 monolayer thick QWs emitting below 250 nm with an internal quantum efficiency (IQE) as high as similar to 30% at room temperature under weak excitation. Variational calculations of the QW exciton properties indicate that the observed high IQE can result from strong three-dimensional localization of the excitons confined in the narrow QWs. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim
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| 5. |
- Toropov, A. A., et al.
(författare)
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Suppression of the quantum-confined Stark effect in AlxGa1-xN/AlyGa1-yN corrugated quantum wells
- 2013
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 114:12
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Tidskriftsartikel (refereegranskat)abstract
- We report comparative studies of 6-nm-thick AlxGa1-xN/AlyGa1-yN pyroelectric quantum wells (QWs) grown by plasma-assisted molecular beam epitaxy on c-sapphire substrates with a thick AlN buffer deposited under different growth conditions. The Al-rich growth conditions result in a 2D growth mode and formation of a planar QW, whereas the N-rich conditions lead to a 3D growth mode and formation of a QW corrugated on the size scale of 200-300 nm. Time-resolved photoluminescence (PL) measurements reveal a strong quantum-confined Stark effect in the planar QW, manifested by a long PL lifetime and a red shift of the PL line. In the corrugated QW, the emission line emerges 200 meV higher in energy, the low-temperature PL lifetime is 40 times shorter, and the PL intensity is stronger (similar to 4 times at 4.5K and similar to 60 times at 300 K). The improved emission properties are explained by suppression of the quantum-confined Stark effect due to the reduction of the built-in electric field within the QW planes, which are not normal to the [0001] direction, enhanced carrier localization, and improved efficiency of light extraction.
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| 6. |
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| 7. |
- Jiang, R. C., et al.
(författare)
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Increased CSF-decorin predicts brain pathological changes driven by Alzheimer's A beta amyloidosis
- 2022
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Ingår i: Acta Neuropathologica Communications. - : Springer Science and Business Media LLC. - 2051-5960. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Cerebrospinal fluid (CSF) biomarkers play an important role in diagnosing Alzheimer's disease (AD) which is characterized by amyloid-beta (A beta) amyloidosis. Here, we used two App knock-in mouse models, App(NL-F/NL-F) and App(NL-G-F/NL-G-F), exhibiting AD-like A beta pathology to analyze how the brain pathologies translate to CSF proteomes by label-free mass spectrometry (MS). This identified several extracellular matrix (ECM) proteins as significantly altered in App knock-in mice. Next, we compared mouse CSF proteomes with previously reported human CSF MS results acquired from patients across the AD spectrum. Intriguingly, the ECM protein decorin was similarly and significantly increased in both App(NL-F/NL-F) and App(NL-G-F/NL-G-F) mice, strikingly already at three months of age in the App(NL-F/NL-F) mice and preclinical AD subjects having abnormal CSF-A beta 42 but normal cognition. Notably, in this group of subjects, CSF-decorin levels positively correlated with CSF-A beta 42 levels indicating that the change in CSF-decorin is associated with early A beta amyloidosis. Importantly, receiver operating characteristic analysis revealed that CSF-decorin can predict a specific AD subtype having innate immune activation and potential choroid plexus dysfunction in the brain. Consistently, in App(NL-F/NL-F) mice, increased CSF-decorin correlated with both AP plaque load and with decorin levels in choroid plexus. In addition, a low concentration of human A beta 42 induces decorin secretion from mouse primary neurons. Interestingly, we finally identify decorin to activate neuronal autophagy through enhancing lysosomal function. Altogether, the increased CSF-decorin levels occurring at an early stage of A beta amyloidosis in the brain may reflect pathological changes in choroid plexus, present in a subtype of AD subjects.
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