| 1. |
- Mikhailov, T. N., et al.
(författare)
-
Forster Energy Transfer in Arrays of Epitaxial CdSe/ZnSe Quantum Dots Involving Bright and Dark Excitons
- 2018
-
Ingår i: Physics of the solid state. - : PLEIADES PUBLISHING INC. - 1063-7834 .- 1090-6460. ; 60:8, s. 1590-1594
-
Tidskriftsartikel (refereegranskat)abstract
- Using time-resolved photoluminescence (PL) spectroscopy, we establish the presence of the Forster energy transfer mechanism between two arrays of epitaxial CdSe/ZnSe quantum dots (QDs) of different sizes. The mechanism operates through dipole-dipole interaction between ground excitonic states of the smaller QDs and excited states of the larger QDs. The dependence of energy transfer efficiency on the width of barrier separating the QD insets is shown to be in line with the Forster mechanism. The temperature dependence of the PL decay times and PL intensity suggests the involvement of dark excitons in the energy transfer process.
|
|
| 2. |
- Evropeytsev, E. A., et al.
(författare)
-
Coexistence of type-I and type-II band line-ups in 1-2 monolayer thick GaN/AlN single quantum wells
- 2017
-
Ingår i: 4TH INTERNATIONAL SCHOOL AND CONFERENCE ON OPTOELECTRONICS, PHOTONICS, ENGINEERING AND NANOSTRUCTURES (SAINT PETERSBURG OPEN 2017). - : IOP PUBLISHING LTD.
-
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.
|
|
| 3. |
- Evropeytsev, E. A., et al.
(författare)
-
Structural properties and vertical transport in ZnSe/CdSe superlattices grown on an In0.3Ga0.7As metamorphic buffer layer
- 2016
-
Ingår i: PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 13 NO 7-9. - : WILEY-V C H VERLAG GMBH. ; , s. 503-506
-
Konferensbidrag (refereegranskat)abstract
- We report on the growth by molecular-beam epitaxy of short-period ZnSe/ CdSe superlattices (SLs) on an In0.3Ga0.7As metamorphic buffer layer. Such SLs are considered as a promising material for a wide band-gap photoactive p-n junction in a hybrid monolithic Ge/InxGa1-xAs/In-y(Al,Ga)(1-y)As/II-VI solar cell. Lattice-matching of the SLs to the In0.3Ga0.7As layer is confirmed by X-ray diffractometry. Vertical transport of photoexcited carriers is investigated by means of both steady state and time-resolved photoluminescence techniques in heterostructures containing the ZnSe/CdSe SL with an enlarged quantum well (EQW). Characteristic times of the carrier transport across the SL towards EQW are evaluated in the temperature range 120-300 K. (C) 2016 WILEY-VCH Verlag GmbH amp; Co.
|
|
| 4. |
- Grinchuk, P. S., et al.
(författare)
-
Effect of technological parameters on densification of reaction bonded Si/SiC ceramics
- 2018
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier Ltd. - 0955-2219 .- 1873-619X. ; 38:15, s. 4815-4823
-
Tidskriftsartikel (refereegranskat)abstract
- Si/SiC composite ceramics was produced by reaction sintering method in process of molten silicon infiltration into porous C/SiC preform fabricated by powder injection molding followed by impregnation with phenolic resin and carbonization. To optimize the ceramics densification process, effect of slurry composition, debinding conditions and the key parameters of all technological stages on the Si/SiC composite characteristics was studied. At the stage of molding the value of solid loading 87.5% was achieved using bimodal SiC powder and paraffin-based binder. It was found that the optimal conditions of fast thermal debinding correspond to the heating rate of 10 °C/min in air. The porous C/SiC ceramic preform carbonized at 1200 °C contained 4% of pyrolytic carbon and ∼25% of open pores. The bulk density of Si/SiC ceramics reached 3.04 g/cm3, silicon carbide content was 83–85 wt.% and residual porosity did not exceed 2%.
|
|
| 5. |
- Mikhailov, T. N., et al.
(författare)
-
Recombination dynamics in heterostructures with two planar arrays of II-VI quantum dots
- 2016
-
Ingår i: 3RD INTERNATIONAL SCHOOL AND CONFERENCE ON OPTOELECTRONICS, PHOTONICS, ENGINEERING AND NANOSTRUCTURES (SAINT PETERSBURG OPEN 2016). - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)abstract
- We present time-resolved photoluminescence studies of epitaxial heterostructures with two arrays of Cd(Zn)Se/ZnSe quantum dots (QDs), which are formed by the successive insertion of CdSe fractional monolayers of different nominal thicknesses into a ZnSe matrix. Our data are suggestive of the appearance of effective channels of the energy transfer from the insertion comprising the array with smaller QDs, emitting at higher energy, towards the array with larger QDs, emitting at lower energy. The effect of dark excitons on characteristic times of radiative recombination is discussed.
|
|
| 6. |
- Mikhailov, T. N., et al.
(författare)
-
Suppression of slow decaying emission in II-VI quantum dots with Forster resonance energy transfer
- 2017
-
Ingår i: 4TH INTERNATIONAL SCHOOL AND CONFERENCE ON OPTOELECTRONICS, PHOTONICS, ENGINEERING AND NANOSTRUCTURES (SAINT PETERSBURG OPEN 2017). - : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)abstract
- We report on time-resolved photoluminescence studies of Forster resonance energy transfer (FRET) in structures with two arrays of epitaxial Cd(Zn)Se quantum dots (QDs) of different sizes separated by the ZnSe barrier of a variable width. The acceleration of recombination rate of both fast and slowly decaying components of emission from the energy-donating small QDs with the decrease of the barrier width is well consistent with the FRET mechanism. The found Forster radii turn out to be different for the fast and slow components. The rate acceleration is accompanied by the strong suppression of the slow emission component related, presumably, to the dark excitons. These findings open a way to control the characteristic of QD-based devices.
|
|
| 7. |
- Shubina, T. V., et al.
(författare)
-
Recombination dynamics in arrays of II-VI epitaxial quantum dots with Forster resonance energy transfer
- 2017
-
Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 254:4
-
Tidskriftsartikel (refereegranskat)abstract
- We report on time-resolved photoluminescence (TR PL) studies of Forster resonance energy transfer (FRET) between epitaxial CdSe/ZnSe quantum dots (QDs). To prove the existence of FRET, we use two sheets of QD arrays, formed from CdSe insertions of different nominal thicknesses, which are separated by a ZnSe barrier of a variable width. The FRET mechanism manifests itself as acceleration of the PL decay of the energy-donating QD sheet when the barrier width is decreased. The Forster radius of about 10.5nm is determined by fitting TR PL data. Besides, our findings exhibit the inhomogeneous distribution of QD sizes within the QD arrays and the influence of FRET efficiency on recombination dynamics of forbidden exciton states. TR PL images showing the acceleration of PL decay of the energy-donating QD array with decreasing the barrier width.
|
|
| 8. |
- Toropov, A. A., et al.
(författare)
-
AlGaN nanostructures with extremely high quantum yield at 300 K
- 2016
-
Ingår i: Physics of the solid state. - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 1063-7834 .- 1090-6460. ; 58:11, s. 2261-2266
-
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.
|
|
| 9. |
- Toropov, A. A., et al.
(författare)
-
AlGaN Nanostructures with Extremely High Room-Temperature Internal Quantum Efficiency of Emission Below 300 nm
- 2017
-
Ingår i: Journal of Electronic Materials. - : SPRINGER. - 0361-5235 .- 1543-186X. ; 46:7, s. 3888-3893
-
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.
|
|
| 10. |
- Toropov, A. A., et al.
(författare)
-
Exciton recombination in spontaneously formed and artificial quantum wells AlxGa1-xN/AlyGa1-yN (x < y similar to 0.8)
- 2016
-
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
-
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
|
|
