| 1. |
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| 2. |
- Evropeytsev, E. A., et al.
(författare)
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Coexistence of type-I and type-II band line-ups in 1-2 monolayer thick GaN/AlN single quantum wells
- 2017
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Ingår i: 4TH INTERNATIONAL SCHOOL AND CONFERENCE ON OPTOELECTRONICS, PHOTONICS, ENGINEERING AND NANOSTRUCTURES (SAINT PETERSBURG OPEN 2017). - : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- GaN/AlN quantum wells (QWs) with varied nominal thickness of 0.5-4 monolayers have been studied by time-resolved photoluminescence (PL) spectroscopy. The structures demonstrate an emission peak with the thickness-dependent wavelength in the range 225-320 nm. The observed temporal behavior of PL between 225 and 280 nm can be described as a superposition of fast and slow decaying components with characteristic decay time constants of the order of 0.1-0.7 ns and 7-30 ns, respectively. The fast PL component with the decay time smaller than 1 ns dominates in the thicker GaN insertions and tends to vanish in the thinnest ones, where the slow PL component becomes progressively longer. These observations imply formation in the GaN/AlN monolayer-thick layers of an inhomogeneous excitonic system involving both direct and indirect in space excitons.
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| 3. |
- Jmerik, V.N., et al.
(författare)
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Optically pumped lasing at 300.4 nm in AlGaN MQW structures grown by plasma-assisted molecular beam epitaxy on c-Al2O3
- 2010
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Ingår i: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE. - : WILEY-V C H VERLAG GMBH. - 1862-6300. ; 207:6, s. 1313-1317
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Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated optically pumped room-temperature pulse lasing at 300.4 nm from an AlGaN-based multiple-quantum-well (MQW) structure grown by plasma-assisted molecular beam epitaxy on a c-sapphire substrate. The lasing was achieved at the threshold peak power of similar to 12 MW/cm(2). The MQW structure involved AlGaN/AlN short-period super-lattices to decrease the threading dislocation densities from 10(11) down to 10(9)-10(10) cm(-2). Studies of time-resolved photoluminescence (TRPL) spectra and cw PL temperature dependences (10-300K) of different MQW structures, as well as numerical calculations of the optical gain and confinement in the laser structure allowed us to conclude about the optimum design of AlGaN-based MQW structures for the lower threshold UV lasing.
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| 4. |
- Jmerik, V. N., et al.
(författare)
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Site-Controlled Growth of GaN Nanorods with Inserted InGaN Quantum Wells on mu-Cone Patterned Sapphire Substrates by Plasma-Assisted MBE
- 2018
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Ingår i: Semiconductors (Woodbury, N.Y.). - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 1063-7826 .- 1090-6479. ; 52:5, s. 667-670
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new approach to fabricate regular arrays of GaN nanorods (NRs) with InGaN QWs by plasma-assisted molecular-beam epitaxy (PA MBE) on micro-cone patterned sapphire substrates (mu-CPSSs). A two-stage PA MBE fabrication process of GaN NRs has been developed, starting with a high temperature nucleation layer growth at metal-rich conditions to aggregate selectively GaN nucleus on c-oriented areas of the mu-CPSSs and followed by growth of 1-mu m-thick GaN NRs at strongly nitrogen-rich conditions exactly on the cone tips. These results are explained by energetically favorable GaN growth on the (000 (1) over bar) oriented sapphire surface. Both micro-photoluminescence and micro-cathodoluminescence confirm the formation of regular array of optically and spectrally isolated NRs without usage of any nanolithography.
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| 5. |
- Kazanov, D. R., et al.
(författare)
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Ring resonator optical modes in InGaN/GaN structures grown on micro-cone-patterned sapphire substrates
- 2018
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Ingår i: 19TH RUSSIAN YOUTH CONFERENCE ON PHYSICS OF SEMICONDUCTORS AND NANOSTRUCTURES, OPTO- AND NANOELECTRONICS. - : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- Molecular beam epitaxy (MBE) of III-nitride compounds on specially prepared cone-shaped patterned substrates is being actively developed nowadays, especially for nanophotonic applications. This type of substrates enables the successful growth of hexagonal nanorods (NRs). The insertion of an active quantum-sized region of InGaN inside a GaN NR allows us to enhance the rate of optical transitions by coupling them with resonant optical modes in the NR. However, we have observed the enhancement of emission not only from the NR but also around the circumference region of the cone-shaped base. We have studied this specific feature and demonstrated its impact on the output signal.
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| 6. |
- Nechaev, D. V., et al.
(författare)
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Site-controlled GaN nanocolumns with InGaN insertions grown by MBE
- 2017
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Ingår i: 4TH INTERNATIONAL SCHOOL AND CONFERENCE ON OPTOELECTRONICS, PHOTONICS, ENGINEERING AND NANOSTRUCTURES (SAINT PETERSBURG OPEN 2017). - : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- The site-controlled plasma-assisted molecular beam epitaxy (PA MBE) has been developed to fabricate the regular array of GaN nanocolumns (NCs) with InGaN insertions on micro-cone patterned sapphire substrates (mu-CPSSs). Two-stage growth of GaN NCs, including a nucleation layer grown at metal-rich conditions and high temperature GaN growth in strong N-rich condition, has been developed to achieve the selective growth of the NCs. Micro-cathodoluminescence measurements have demonstrated pronounced emission from the InGaN insertions in 450-600 nm spectral range. The optically isolated NCs can be used as effective nano-emitters operating in the visible range.
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| 7. |
- 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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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Shubina, Tatiana, et al.
(författare)
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Optical properties of GaN/AlGaN quantum wells with inversion domains
- 2003
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Ingår i: Physica status solidi. A, Applied research. - : Wiley. - 0031-8965 .- 1521-396X. ; 195:3, s. 537-542
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Tidskriftsartikel (refereegranskat)abstract
- Two-band photoluminescence (PL) and respective absorption and reflection features are observed in GaN/AlGaN MBE-grown quantum well (QW) structures of dominant N polarity with inversion domains (IDs). The PL bands are related to transitions in the regions of different polarity, characterized by different strain and electric fields. A micro-PL study reveals sharp and narrow (1.5-2.5 meV) PL lines placed between the bands, which are tentatively attributed to recombination at localization sites associated with intersections of the QWs with the domains. Additionally, we demonstrate that the ID formation decreases the overall strength of the intrinsic electric fields in the QW structures.
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| 12. |
- Shubina, Tatiana, 1950-, et al.
(författare)
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Optical properties of InN related to surface plasmons
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:14, s. 2633-2641
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Tidskriftsartikel (refereegranskat)abstract
- We report on the complex nature of infrared luminescence and absorption in InN films, which cannot be entirely explained by the concept of a conventional narrow-gap semiconductor. In particular, it concerns the detection of peaks near absorption edges by both thermally detected optical absorption and photoluminescence excitation spectroscopy and the observation of extraordinarily strong resonant enhancement of emission. To describe the experimental data a model is proposed, which takes into account surface plasmons in metal-like inclusions, modifying the optical properties of InN. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA,.
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| 13. |
- Shubina, T. V., et al.
(författare)
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III-nitride microcrystal cavities with quasi whispering gallery modes grown by molecular beam epitaxy
- 2016
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Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 253:5, s. 845-852
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes current trends in fabrication of III-nitride microresonators exploiting whispering gallery modes. Novel cup-cavities are proposed and their fabrication from GaN and InN by molecular beam epitaxy on patterned substrates is described. These cup-cavities can concentrate the mode energy in a subwavelength volume. Their mode energies are stable up to room temperature, being identical in large microcrystals. In these cavities, mode switching can be realized by means of refractive index variation. Cup-cavity modes, being inferior to plasmonic resonances in the respect of integral emission enhancement, have advantages for spectrally selective amplification of quantum transitions in site-controlled nano-emitters. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim
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| 14. |
- Shubina, T. V., et al.
(författare)
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III-nitride tunable cup-cavities supporting quasi whispering gallery modes from ultraviolet to infrared
- 2015
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 5:17970
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Tidskriftsartikel (refereegranskat)abstract
- Rapidly developing nanophotonics needs microresonators for different spectral ranges, formed by chip-compatible technologies. In addition, the tunable ones are much in demand. Here, we present site-controlled III-nitride monocrystal cup-cavities grown by molecular beam epitaxy. The cup-cavities can operate from ultraviolet to near-infrared, supporting quasi whispering gallery modes up to room temperature. Besides, their energies are identical in large ripened crystals. In these cavities, the refractive index variation near an absorption edge causes the remarkable effect of mode switching, which is accompanied by the spatial redistribution of electric field intensity with concentration of light into a subwavelength volume. Our results shed light on the mode behavior in semiconductor cavities and open the way for single-growth-run manufacturing the devices comprising an active region and a cavity with tunable mode frequencies.
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| 15. |
- Tkachman, M.G., et al.
(författare)
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Phonon-assisted exciton luminescence in GaN layers grown by MBE and chloride-hydride VPE
- 2003
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Ingår i: Semiconductors (Woodbury, N.Y.). - : Pleiades Publishing Ltd. - 1063-7826 .- 1090-6479. ; 37:5, s. 532-536
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Tidskriftsartikel (refereegranskat)abstract
- Optical properties of GaN layers grown by the molecular-beam epitaxy (MBE) and chloride-hydride vapor-phase epitaxy (CHVPE) have been studied, and the quality of two types of samples has been compared. The photoluminescence spectra have an excitonic nature for both types of layers. To determine precisely the nature of exciton transitions, the reflectance spectra were studied. A key point was the investigation of phonon-assisted exciton luminescence, which provides information on the density distribution of the exciton states. Temperature dependences of the exciton transition energy and the ratio of intensities of one- and two-phpnon replicas were studied. The high quality of both types of layers has been confirmed, though the concentration of acceptors in MBE-grown samples is higher than in CHVPE samples. © 2003 MAIK "Nauka/Interperiodica".
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| 16. |
- 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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| 17. |
- 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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| 18. |
- 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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| 19. |
- 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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