| 11. |
- Fadlallah, Mohamed M., et al.
(författare)
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Theoretical study on electronic, optical, magnetic and photocatalytic properties of codoped SrTiO3 for green energy application
- 2022
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Ingår i: MICRO AND NANOSTRUCTURES. - : ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. - 2773-0123. ; 168
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the large scientific interest in development of double cation doping of SrTiO3 (STO) within the last years aiming to improve the water-splitting activity, electronic and ionic conductivity of STO, we study the effect of (La, X) and (Y, M) codoping (X = Al/Sc/Cr/Mn/Fe/Co/Ni/Mo, and M = Al/Cr/Mo) on the structure, electronic, magnetic, optical and photocatalytic properties (for water-splitting and CO2 reduction) of STO using spin-polarized hybrid density functional theory. In most considered cases, the X and M monodoping reduces the bandgap of STO more than the (La, X) and (Y, M) codoping, except for the case of (La, Ni) codoping. We found out La-/Y-doping, and (La/Y, Al)-/(La, Sc)-codoping cannot improve the conductivity of STO, while other monodopants and codopants can increase it. Our calculations have revealed that the best suited candidates for mono-/co-doped STO-based photocatalysts are Fe-/(La, Ni)-STO. Furthermore, we disclosed Fe-/Mn-/(La, Mn/Fe/Ni)-STO could be appropriate for spintronic applications.
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| 12. |
- Gogova, Daniela, et al.
(författare)
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Epitaxial growth of β -Ga 2 O 3 by hot-wall MOCVD
- 2022
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5, s. 055022-055022
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Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and highperformance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth ofβ-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures(740 ○C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. Thehot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a 201 ¯rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) ¯ β-Ga2O3 substrates, indicative ofsimilar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be furtherexplored for the fabrication of β-Ga2O3
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| 13. |
- Gogova, Daniela, 1967-, et al.
(författare)
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Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
- 2022
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5
-
Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of beta-Ga2O3. Epitaxial beta-Ga2O3 layers at high growth rates (above 1 mu m/h), at low reagent flows, and at reduced growth temperatures (740 degrees C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial beta-Ga2O3 layers are demonstrated with a 201 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) beta-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of beta-Ga2O3.
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| 14. |
- Scajev, Patrik, et al.
(författare)
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Long-lived excitons in thermally annealed hydrothermal ZnO
- 2024
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Ingår i: Heliyon. - : CELL PRESS. - 2405-8440. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Applying thermal annealing to hydrothermal ZnO crystals an enhancement of exciton lifetime from 80 ps to 40 ns was achieved boosting PL quantum efficiency of the UV luminescence up to 70 %. The lifetime improvement is related to the reduced density of carrier traps by a few orders of magnitude as revealed by the reduction of the slow decay tail in pump probe decays coupled with weaker defects-related PL. The diffusion coefficient was determined to be 0.5 cm(2)/s, providing a large exciton diffusion length of 1.4 mu m. The UV PL lifetime drop at the lowest exciton densities was explained by capture to traps. Release of holes from acceptor traps provided delayed exciton luminescence with similar to 200 mu s day time and 390 meV thermal activation energy. Pump-probe decays provided exciton absorption cross-section of 9 x 10(-18) cm(2) at 1550 nm wavelength and verified the PL decay times of excitons. Amplitudes and decay times of the microsecond slow decay tails have been correlated with the trap densities and their photoluminescence. A surface recombination velocity of 500 cm/s and the bimolecular free carrier recombination coefficient 0.7 x 10(-11) cm(3)/s were calculated. Therefore, the properly annealed hydrothermally grown ZnO can be a viable and integral part of many functional devices as light-emitting diodes and lasers.
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| 15. |
- Stanishev, Vallery, et al.
(författare)
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Low Al-content n-type AlxGa1−xN layers with a high-electron-mobility grown by hot-wall metalorganic chemical vapor deposition
- 2023
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Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we demonstrate the capability of the hot-wall metalorganic chemical vapor deposition to deliver high-quality n-AlxGa1−xN (x = 0 – 0.12, [Si] = 1×1017 cm−3) epitaxial layers on 4H-SiC(0001). All layers are crack-free, with a very small root mean square roughness (0.13 – 0.25 nm), homogeneous distribution of Al over film thickness and a very low unintentional incorporation of oxygen at the detection limit of 5×1015 cm−3 and carbon of 2×1016 cm−3. Edge type dislocations in the layers gradually increase with increasing Al content while screw dislocations only raise for x above 0.077. The room temperature electron mobility of the n-AlxGa1−xN remain in the range of 400 – 470 cm2/(V.s) for Al contents between 0.05 and 0.077 resulting in comparable or higher Baliga figure of merit with respect to GaN, and hence demonstrating their suitability for implementation as drift layers in power device applications. Further increase in Al content is found to result in significant deterioration of the electrical properties.
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| 16. |
- Vodopyanov, Alexander, et al.
(författare)
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A new plasma-based approach to hydrogen intercalation of graphene
- 2021
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Ingår i: Superlattices and Microstructures. - : ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. - 0749-6036 .- 1096-3677. ; 160
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Tidskriftsartikel (refereegranskat)abstract
- In this work a new plasma-based approach to hydrogen intercalation of Graphene grown on SiC is demonstrated. By optimization of the inductively coupled plasma parameters the intercalated by hydrogen Graphene has been modified gradually and transformed into the two-dimensional hydrocarbon Graphane. The intermediate stages during the transition of Graphene to Graphane were studied by means of Raman spectroscopy and AFM. The dependence of the intensities of the Raman Graphene fingerprints: D and G peaks on the hydrogen intercalation time has been studied. The changes of resistance during the hydrogen plasma treatment were parsed. The Raman (D + D ) peak corresponding to hydrogenated graphene was studied in detail. The method developed is highly reliable and flexible as well as convenient for large-scale fabrication of Graphane to be employed as a hydrogen storage material and in 2D electronics.
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