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Darakchieva, Vanya, ProfessorORCID iD iconorcid.org/0000-0002-8112-7411
Alternative names
Publications (10 of 120) Show all publications
Gribisch, P., Delgado Carrascon, R., Darakchieva, V. & Lind, E. (2023). Tuning of Quasi-Vertical GaN FinFETs Fabricated on SiC Substrates. IEEE Transactions on Electron Devices, 70(5), 2408-2414
Open this publication in new window or tab >>Tuning of Quasi-Vertical GaN FinFETs Fabricated on SiC Substrates
2023 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 70, no 5, p. 2408-2414Article in journal (Refereed) Published
Abstract [en]

In this work, we present the fabrication and investigation of the properties of quasi-vertical gallium nitride (GaN) fin field effect transistors (FinFETs) on silicon carbide (SiC) substrates and the influence of a postgate metallization annealing (PMA). The devices reveal low subthreshold swings (SSs) down to around 70 mV/dec. For a 1- μm -thick drift layer, a low ON-resistance below 0.05 mΩ⋅ cm2 (normalized on the fin area) and a breakdown voltage of 60 V were obtained. Devices with included PMA show a decreased threshold voltage and ON-resistance and by several orders of magnitude reduced gate leakage current compared to non-annealed devices. The devices show ohmic contact behavior and slightly negative threshold voltages, which indicates normally- ON behavior. The effective and field-effect mobility of the fin channel was obtained with a modeled carrier concentration and reveal to around 70 and 13 cm2/(Vs) at high gate voltages, which is in a good comparison to so far reported similar devices.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Keywords
Fin field effect transistor (FinFET), gallium nitride (GaN), quasi-vertical, silicon carbide (SiC)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-193272 (URN)10.1109/TED.2023.3263154 (DOI)000973178200001 ()
Funder
Vinnova, 2022-03139Swedish Research Council, 2016-00889Swedish Foundation for Strategic Research, RIF14-055 and EM16-0024
Note

Funding: Swedish Governmental Agency for Innovation Systems (VINNOVA) [2022-03139]; Swedish Research Council (VR) [2016-00889]; Swedish Foundation for Strategic Research [RIF14-055, EM16-0024]

Available from: 2023-04-27 Created: 2023-04-27 Last updated: 2023-12-28
Karki, A., Cincotti, G., Chen, S., Stanishev, V., Darakchieva, V., Wang, C., . . . Jonsson, M. (2022). Electrical Tuning of Plasmonic Conducting Polymer Nanoantennas. Advanced Materials, 34(13), Article ID 2107172.
Open this publication in new window or tab >>Electrical Tuning of Plasmonic Conducting Polymer Nanoantennas
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2022 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 34, no 13, article id 2107172Article in journal (Refereed) Published
Abstract [en]

Nanostructures of conventional metals offer manipulation of light at the nanoscale but are largely limited to static behavior due to fixed material properties. To develop the next frontier of dynamic nano-optics and metasurfaces, this study utilizes the redox-tunable optical properties of conducting polymers, as recently shown to be capable of sustaining plasmons in their most conducting oxidized state. Electrically tunable conducting polymer nano-optical antennas are presented, using nanodisks of poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) as a model system. In addition to repeated on/off switching of the polymeric nanoantennas, the concept enables gradual electrical tuning of the nano-optical response, which was found to be related to the modulation of both density and mobility of the mobile polaronic charge carriers in the polymer. The resonance position of the PEDOT:Sulf nanoantennas can be conveniently controlled by disk size, here reported down to a wavelength of around 1270 nm. The presented concept may be used for electrically tunable metasurfaces, with tunable farfield as well as nearfield. The work thereby opens for applications ranging from tunable flat meta-optics to adaptable smart windows.

Place, publisher, year, edition, pages
Wiley-V C H Verlag GMBH, 2022
Keywords
conducting polymers; dynamic plasmonic nanoantennas; electrical tuning; tunable metasurfaces
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-183215 (URN)10.1002/adma.202107172 (DOI)000756620400001 ()35064601 (PubMedID)
Note

Funding Agencies|Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Research Council (VR)Swedish Research Council [2020-00287]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

Available from: 2022-03-01 Created: 2022-03-01 Last updated: 2023-12-28Bibliographically approved
Gogova, D., Ghezellou, M., Tran, D. Q., Richter, S., Papamichail, A., ul-Hassan, J., . . . Darakchieva, V. (2022). Epitaxial growth of β-Ga2O3 by hot-wall MOCVD. AIP Advances, 12(5), Article ID 055022.
Open this publication in new window or tab >>Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
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2022 (English)In: AIP Advances, E-ISSN 2158-3226, Vol. 12, no 5, article id 055022Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
AIP Publishing, 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-185208 (URN)10.1063/5.0087571 (DOI)000797911600007 ()
Funder
Swedish Energy Agency, P45396-1Vinnova, 2016-05190Swedish Research Council, 2016-00889Swedish Research Council, 2017-03714Knut and Alice Wallenberg Foundation, 2018.0071
Note

Funding: Swedish Energy Agency [P45396-1]; Swedish Governmental Agency for Innovation Systems (VINNOVA) [2016-05190]; Ericsson; Gotmic; Swedish Research Council VR [2016-00889, 2017-03714]; Swedish Foundation for Strategic Research [RIF14-055, RIF14-074, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University; SFO Mat LiU [2009-00971]; National Science Foundation (NSF); NSF [DMR 1808715]; Linkoeping University [OIA-2044049]; NSF/EPSCoR RII Track-1: Emergent Quantum Materials and Technologies (EQUATE); Chalmers University of Technology [FA9550-18-1-0360, FA9550-19-S-0003, FA9550-21-1-0259]; Air Force Office of Scientific Research; Epiluvac; KAW Foundation; FMV; Hexagem; Hitachi Energy; On Semiconductor; Saab; SweGaN; UMS

Available from: 2022-05-18 Created: 2022-05-18 Last updated: 2023-03-28Bibliographically approved
Delgado Carrascon, R., Richter, S., Nawaz, M., Paskov, P. P. & Darakchieva, V. (2022). Hot-Wall MOCVD for High-Quality Homoepitaxy of GaN: Understanding Nucleation and Design of Growth Strategies. Crystal Growth & Design, 22(12), 7021-7030
Open this publication in new window or tab >>Hot-Wall MOCVD for High-Quality Homoepitaxy of GaN: Understanding Nucleation and Design of Growth Strategies
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2022 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 22, no 12, p. 7021-7030Article in journal (Refereed) Published
Abstract [en]

Thick GaN layers with a low concentration of defects are the key to enable next-generation vertical power electronic devices. Here, we explore hot-wall metalorganic chemical vapor deposition (MOCVD) for the development of GaN homoepitaxy. We propose a new approach to grow high quality homoepitaxial GaN in N2-rich carrier gas and at a higher supersaturation as compared to heteroepitaxy. We develop a low temperature GaN as an optimum nucleation scheme based on the evolution and thermal stability of the GaN surface under different gas compositions and temperatures. Analysis in the framework of nucleation theory of homoepitaxial layers simultaneously grown on GaN templates on SiC and on hydride vapor phase epitaxy GaN substrates is presented. We show that residual strain and screw dislocation densities affect GaN nucleation and subsequent growth leading to distinctively different morphologies of GaN homoepitaxial layers grown on GaN templates and native substrates, respectively. The established comprehensive picture provides a guidance for designing strategies for growth conditions optimization in GaN homoepitaxy. GaN with atomically flat and smooth epilayer surfaces with a root-mean-square roughness value as low as 0.049 nm and low background carbon concentration of 5.3 x 1015 cm-3 has been achieved. It is also shown that there is no generation of additional dislocations during homoepitaxial growth. Thus, our results demonstrate the potential of the hot-wall MOCVD technique to deliver high-quality GaN material for vertical power devices.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-190211 (URN)10.1021/acs.cgd.2c00683 (DOI)000883760600001 ()
Note

Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) [2016-05190]; Linkoping University; Chalmers University of technology; Ericsson; Epiluvac; FMV; Gotmic; Hexagem; Hitachi Energy Research; On Semiconductor; Saab; SweGaN; aUMS; Volvo Cars; Swedish Research Council VR [2016-00889]; Swedish Foundation for Strategic Research [RIF14-055, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University, Faculty Grant [2009-00971]; NanoLund

Available from: 2022-11-29 Created: 2022-11-29 Last updated: 2023-12-28Bibliographically approved
Kakanakova-Georgieva, A., Papamichail, A., Stanishev, V. & Darakchieva, V. (2022). Incorporation of Magnesium into GaN Regulated by Intentionally Large Amounts of Hydrogen during Growth by MOCVD. Physica status solidi. B, Basic research, 259(10), Article ID 2200137.
Open this publication in new window or tab >>Incorporation of Magnesium into GaN Regulated by Intentionally Large Amounts of Hydrogen during Growth by MOCVD
2022 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 259, no 10, article id 2200137Article in journal (Refereed) Published
Abstract [en]

Herein, metal-organic chemical vapor deposition (MOCVD) of GaN layers doped with Mg atoms to the recognized optimum level of [Mg] approximate to 2 x 10(19) cm(-3) is performed. In a sequence of MOCVD runs, operational conditions, including temperature and flow rate of precursors, are maintained except for intentionally larger flows of hydrogen carrier gas fed into the reactor. By employing the largest hydrogen flow of 25 slm in this study, the performance of the as-grown Mg-doped GaN layers is certified by a room-temperature hole concentration of p approximate to 2 x 10(17) cm(-3) in the absence of any thermal activation treatment. Experimental evidence is delivered that the large amounts of hydrogen during the MOCVD growth can regulate the incorporation of the Mg atoms into GaN in a significant way so that MgH complex can coexist with a dominant and evidently electrically active isolated Mg-Ga acceptor.

Place, publisher, year, edition, pages
Wiley-V C H Verlag GMBH, 2022
Keywords
gallium nitride; hydrogen; metal-organic chemical vapor deposition; p-type doping
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-186495 (URN)10.1002/pssb.202200137 (DOI)000811116800001 ()
Note

Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program [2016-05190]; Linkoping University; Chalmers University of technology; Ericsson; Epiluvac; FMV; Gotmic; Hexagem; Hitachi Energy; On Semiconductor; Saab; SweGaN; UMS; Swedish Research Council VR [2016-00889]; Swedish Foundation for Strategic Research [RIF14-055, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University, Faculty Grant SFO Mat LiU [2009-00971]

Available from: 2022-06-28 Created: 2022-06-28 Last updated: 2024-03-01Bibliographically approved
Stokey, M., Gramer, T., Korlacki, R., Knight, S. R., Richter, S., Jinno, R., . . . Schubert, M. (2022). Infrared-active phonon modes and static dielectric constants in α-(AlxGa1−x)2O3 (0.18  ≤ x  ≤ 0.54) alloys. Applied Physics Letters, 120(11), Article ID 112202.
Open this publication in new window or tab >>Infrared-active phonon modes and static dielectric constants in α-(AlxGa1−x)2O3 (0.18  ≤ x  ≤ 0.54) alloys
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2022 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 120, no 11, article id 112202Article in journal (Refereed) Published
Abstract [en]

We determine the composition dependence of the transverse and longitudinal optical infrared-active phonon modes in rhombohedral α-(AlxGa1−x)2O3 alloys by far-infrared and infrared generalized spectroscopic ellipsometry. Single-crystalline high quality undoped thin-films grown on m-plane oriented α-Al2O3 substrates with x = 0.18, 0.37, and 0.54 were investigated. A single mode behavior is observed for all phonon modes, i.e., their frequencies shift gradually between the equivalent phonon modes of the isostructural binary parent compounds. We also provide physical model line shape functions for the anisotropic dielectric functions. We use the anisotropic high-frequency dielectric constants for polarizations parallel and perpendicular to the lattice c axis measured recently by Hilfiker et al. [Appl. Phys. Lett. 119, 092103 (2021)], and we determine the anisotropic static dielectric constants using the Lyddane–Sachs–Teller relation. The static dielectric constants can be approximated by linear relationships between those of α-Ga2O3 and α-Al2O3. The optical phonon modes and static dielectric constants will become useful for device design and free charge carrier characterization using optical techniques. 

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-185206 (URN)10.1063/5.0085958 (DOI)000827449100006 ()2-s2.0-85126835203 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, Wide-Bandgap semiconductors for next generation quantum componentsSwedish Energy Agency, P453396-1Swedish Foundation for Strategic Research, RIF14-055Swedish Foundation for Strategic Research, EM16-0024Vinnova, 2016-05190
Note

Funding: National Science Foundation (NSF) [NSF DMR 1808715]; NSF/EPSCoR RII Track-1: Emergent Quantum Materials and Technologies (EQUATE) [OIA-2044049]; Air Force Office of Scientific Research [FA9550-18-10360, FA9550-19-S-0003, FA9550-21-1-0259]; ACCESS, an AFOSR Center of Excellence [FA9550-18-10529]; Knut and Alice Wallenbergs Foundation; University of Nebraska Foundation; J. A. Woollam Foundation; JSPS Overseas Challenge Program for Young Researchers [1080033]; Swedish Research Council VR Award [201600889]; Swedish Energy Agency [P453396-1]; Swedish Foundation for Strategic Research Grant [RIF14055, EM16-0024]; Swedish Governmental Agency for Innovation Systems VINNOVA under the Competence Center Program [2016-05190]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Link_oping University, Faculty Grant SFO Mat LiU [2009-00971]

Available from: 2022-05-18 Created: 2022-05-18 Last updated: 2022-08-26Bibliographically approved
Tran, D., Delgado Carrascon, R., Muth, J. F., Paskova, T., Nawaz, M., Darakchieva, V. & Paskov, P. P. (2021). Correction: Erratum: “Phonon-boundary scattering and thermal transport in AlxGa1−xN: Effect of layer thickness” [Appl. Phys. Lett. 117, 252102 (2020)]. Applied Physics Letters, 118(18), Article ID 189901.
Open this publication in new window or tab >>Correction: Erratum: “Phonon-boundary scattering and thermal transport in AlxGa1−xN: Effect of layer thickness” [Appl. Phys. Lett. 117, 252102 (2020)]
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2021 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 118, no 18, article id 189901Article in journal (Other academic) Published
Place, publisher, year, edition, pages
AIP Publishing, 2021
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-179850 (URN)10.1063/5.0054625 (DOI)000698625800013 ()2-s2.0-85105880689 (Scopus ID)
Available from: 2021-10-04 Created: 2021-10-04 Last updated: 2023-12-28Bibliographically approved
Chen, S., Kang, E. S. H., Shiran Chaharsoughi, M., Stanishev, V., Kuhne, P., Sun, H., . . . Jonsson, M. (2020). Conductive polymer nanoantennas for dynamic organic plasmonics. Nature Nanotechnology, 15
Open this publication in new window or tab >>Conductive polymer nanoantennas for dynamic organic plasmonics
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2020 (English)In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 15Article in journal (Refereed) Published
Abstract [en]

Being able to dynamically shape light at the nanoscale is oneof the ultimate goals in nano-optics1. Resonant light–matterinteraction can be achieved using conventional plasmonicsbased on metal nanostructures, but their tunability is highlylimited due to a fixed permittivity2. Materials with switchablestates and methods for dynamic control of light–matterinteraction at the nanoscale are therefore desired. Here weshow that nanodisks of a conductive polymer can supportlocalized surface plasmon resonances in the near-infraredand function as dynamic nano-optical antennas, with their resonancebehaviour tunable by chemical redox reactions. Theseplasmons originate from the mobile polaronic charge carriersof a poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf)polymer network. We demonstrate complete and reversibleswitching of the optical response of the nanoantennasby chemical tuning of their redox state, which modulatesthe material permittivity between plasmonic and dielectricregimes via non-volatile changes in the mobile chargecarrier density. Further research may study different conductivepolymers and nanostructures and explore their usein various applications, such as dynamic meta-optics andreflective displays.

Place, publisher, year, edition, pages
London: Nature Publishing Group, 2020
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-163089 (URN)10.1038/s41565-019-0583-y (DOI)000510815600005 ()2-s2.0-85076515412 (Scopus ID)
Available from: 2020-01-10 Created: 2020-01-10 Last updated: 2023-12-28Bibliographically approved
Tran, D., Delgado Carrascon, R., Muth, J. F., Paskova, T., Nawaz, M., Darakchieva, V. & Paskov, P. P. (2020). Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness. Applied Physics Letters, 117(25), Article ID 252102.
Open this publication in new window or tab >>Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness
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2020 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 117, no 25, article id 252102Article in journal (Refereed) Published
Abstract [en]

Thermal conductivity of AlxGa1-xN layers with 0 <= x <= 0.96 and variable thicknesses is systematically studied by combined thermoreflectance measurements and a modified Callaway model. We find a reduction in the thermal conductivity of AlxGa1-xN by more than one order of magnitude compared to that of GaN, which indicates a strong effect of phonon-alloy scattering. It is shown that the short-mean free path phonons are strongly scattered, which leads to a major contribution of the long-mean free path phonons to the thermal conductivity. In thin layers, the long-mean free path phonons become efficiently scattered by the boundaries, resulting in a further decrease in the thermal conductivity. Also, an asymmetry of thermal conductivity as a function of Al content is experimentally observed and attributed to the mass difference between Ga and Al host atoms.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2020
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-172917 (URN)10.1063/5.0031404 (DOI)000603064200002 ()
Note

Funding Agencies|Swedish Governmental Agency for innovation systems (VINOVA) under Competence Center Program [2016-05190]; Swedish Research Council VRSwedish Research Council [2016-00889, 2017-03714]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [RIF14-055, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University, Faculty Grant SFO Mat LiU [2009-00971]; NSFNational Science Foundation (NSF) [CBET-1336464, DMR-1506159]

Available from: 2021-01-26 Created: 2021-01-26 Last updated: 2023-12-28Bibliographically approved
Schubert, M., Mock, A., Korlacki, R., Knight, S., Galazka, Z., Wagner, G., . . . Darakchieva, V. (2019). Longitudinal phonon plasmon mode coupling in β-Ga2O3. Applied Physics Letters, 114(10), Article ID 102102.
Open this publication in new window or tab >>Longitudinal phonon plasmon mode coupling in β-Ga2O3
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2019 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, no 10, article id 102102Article in journal (Refereed) Published
Abstract [en]

In this letter, we investigate a set of n-type single crystals of monoclinic symmetry beta-Ga2O3 with different free electron concentration values by generalized far infrared and infrared spectroscopic ellipsometry. In excellent agreement with our previous model prediction, we find here by experiment that longitudinal-phonon-plasmon coupled modes are polarized either within the monoclinic plane or perpendicular to the monoclinic plane. As predicted, all modes change the amplitude and frequency with the free electron concentration. The most important observation is that all longitudinal-phonon-plasmon coupled modes polarized within the monoclinic plane continuously change their direction as a function of free electron concentration.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-156100 (URN)10.1063/1.5089145 (DOI)000461512000019 ()2-s2.0-85062885181 (Scopus ID)
Note

Funding Agencies|National Science Foundation [DMR 1808715]; Air Force Office of Scientific Research [FA9550-18-1-0360]; Nebraska Materials Research Science and Engineering Center [DMR 1420645]; Swedish Energy Agency [P45396-1]; Swedish Research Council VR Award [2016-00889]; Swedish Foundation for Strategic Research Grant [FL12-0181, RIF14-055, EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University, Faculty Grant SFO Mat LiU [2009-00971]; University of Nebraska Foundation; J. A. Woollam Foundation

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2023-12-28Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-8112-7411

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