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Hens, Philip
Publications (10 of 14) Show all publications
Hens, P., Zakharov, A. A., Iakimov, T., Syväjärvi, M. & Yakimova, R. (2014). Large area buffer-free graphene on non-polar (001) cubic silicon carbide. Carbon, 80, 823-829
Open this publication in new window or tab >>Large area buffer-free graphene on non-polar (001) cubic silicon carbide
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2014 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 80, p. 823-829Article in journal (Refereed) Published
Abstract [en]

Graphene is, due to its extraordinary properties, a promising material for future electronic applications. A common process for the production of large area epitaxial graphene is a high temperature annealing process of atomically flat surfaces from hexagonal silicon carbide. This procedure is very promising but has the drawback of the formation of a buffer layer consisting of a graphene-like sheet, which is covalently bound to the substrate. This buffer layer degenerates the properties of the graphene above and needs to be avoided. We are presenting the combination of a high temperature process for the graphene production with a newly developed substrate of (0 0 1)-oriented cubic silicon carbide. This combination is a promising candidate to be able to supply large area homogenous epitaxial graphene on silicon carbide without a buffer layer. We are presenting the new substrate and first samples of epitaxial graphene on them. Results are shown using low energy electron microscopy and diffraction, photoelectron angular distribution and X-ray photoemission spectroscopy. All these measurements indicate the successful growth of a buffer free few layer graphene on a cubic silicon carbide surface. On our large area samples also the epitaxial relationship between the cubic substrate and the hexagonal graphene could be clarified.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-112605 (URN)10.1016/j.carbon.2014.09.041 (DOI)000344132400088 ()
Available from: 2014-12-10 Created: 2014-12-05 Last updated: 2017-12-05
Schimmel, S., Kaiser, M., Jokubavicius, V., Ou, Y., Hens, P., Linnarsson, M. K., . . . Wellmann, P. (2014). The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy. Paper presented at EMRS 2013 Spring Meeting, Symposium G. IOP Conference Series: Materials Science and Engineering, 56(1), 012002
Open this publication in new window or tab >>The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy
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2014 (English)In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 56, no 1, p. 012002-Article in journal (Refereed) Published
Abstract [en]

Donor-acceptor co-doped SiC is a promising light converter for novel monolithic all-semiconductor white LEDs due to its broad-band donor-acceptor pair luminescence and potentially high internal quantum efficiency. Besides sufficiently high doping concentrations in an appropriate ratio yielding short radiative lifetimes, long nonradiative lifetimes are crucial for efficient light conversion. The impact of different types of defects is studied by characterizing fluorescent silicon carbide layers with regard to photoluminescence intensity, homogeneity and efficiency taking into account dislocation density and distribution. Different doping concentrations and variations in gas phase composition and pressure are investigated.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-105858 (URN)10.1088/1757-899X/56/1/012002 (DOI)
Conference
EMRS 2013 Spring Meeting, Symposium G
Available from: 2014-04-10 Created: 2014-04-10 Last updated: 2017-12-05Bibliographically approved
Hens, P., Müller, J., Wagner, G., Liljedahl, R., Spiecker, E. & Syväjärvi, M. (2013). Defect generation and annihilation in 3C-SiC-(001) homoepitaxial growth by sublimation. In: Alexander A. Lebedev, Sergey Yu. Davydov, Pavel A. Ivanov and Mikhail E. Levinshtein (Ed.), Silicon Carbide and Related Materials 2012: . Paper presented at 9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St. Petersburg, Russia (pp. 283-286). Trans Tech Publications, 740-742
Open this publication in new window or tab >>Defect generation and annihilation in 3C-SiC-(001) homoepitaxial growth by sublimation
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2013 (English)In: Silicon Carbide and Related Materials 2012 / [ed] Alexander A. Lebedev, Sergey Yu. Davydov, Pavel A. Ivanov and Mikhail E. Levinshtein, Trans Tech Publications , 2013, Vol. 740-742, p. 283-286Conference paper, Published paper (Refereed)
Abstract [en]

In this paper we present an investigation on the defect generation and annihilation during the homoepitaxial growth step of cubic silicon carbide by sublimation epitaxy on templates grown by chemical vapor deposition on silicon substrates. Several structural defects like stacking faults, twins and star-defects show opposite evolution from the template layer into the sublimation grown material. While single planar defects tend to annihilate with increasing layer thickness, the defect clusters assigned to the star-defects are enlarging. These issues contribute to a balance of how to achieve the best possible quality on thick layers.

Place, publisher, year, edition, pages
Trans Tech Publications, 2013
Series
Materials Science Forum, ISSN 0255-5476 ; 740-742
Keywords
3C-SiC, AFM, Defects, Homoepitaxy, Sublimation, TEM, X-Ray Diffraction (XRD)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-96510 (URN)10.4028/www.scientific.net/MSF.740-742.283 (DOI)000319785500067 ()978-3-03785-624-6 (ISBN)
Conference
9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St. Petersburg, Russia
Available from: 2013-08-21 Created: 2013-08-20 Last updated: 2013-08-29Bibliographically approved
Hupfer, T., Hens, P., Kaiser, M., Jokubavicius, V., Syväjärvi, M. & Wellmann, P. (2013). Modeling of the Mass Transport during Homo-Epitaxial Growth of Silicon Carbide by Fast Sublimation Epitaxy. In: : . Paper presented at 9th European Conference on Silicon Carbide & Related Materials (ECSCRM 2012), 2-6 September 2012, Saint-Petersburg, Russia (pp. 52-55). Scientific.Net
Open this publication in new window or tab >>Modeling of the Mass Transport during Homo-Epitaxial Growth of Silicon Carbide by Fast Sublimation Epitaxy
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2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Ballistic and diffusive growth regimes in the Fast Sublimation Growth Process of silicon carbide can be determined using suggested theoretical model for the mean free path calculations. The influences of temperature and inert gas pressure on the mass transport for the growth of epitaxial layers were analyzed theoretically and experimentally.

Place, publisher, year, edition, pages
Scientific.Net, 2013
Series
Materials Science Forum, ISSN 0255-5476 ; 740-742
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-87900 (URN)10.4028/www.scientific.net/MSF.740-742.52 (DOI)000319785500013 ()
Conference
9th European Conference on Silicon Carbide & Related Materials (ECSCRM 2012), 2-6 September 2012, Saint-Petersburg, Russia
Available from: 2013-01-27 Created: 2013-01-27 Last updated: 2017-11-07
Jokubavicius, V., Kaiser, M., Hens, P., Wellmann, P., Liljedahl, R., Yakimova, R. & Syväjärvi, M. (2013). Morphological and Optical Stability in Growth of Fluorescent SiC on Low Off-Axis Substrates. Paper presented at 9th European Conference on Silicon Carbide & Related Materials (ECSCRM 2012), 2-6 September 2012, Saint-Petersburg, Russia. Materials Science Forum, 740-742, 19-22
Open this publication in new window or tab >>Morphological and Optical Stability in Growth of Fluorescent SiC on Low Off-Axis Substrates
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2013 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 740-742, p. 19-22Article in journal (Refereed) Published
Abstract [en]

Fluorescent silicon carbide was grown using the fast sublimation growth process on low off-axis 6H-SiC substrates. In this case, the morphology of the epilayer and the incorporation of dopants are influenced by the Si/C ratio. Differently converted tantalum foils were introduced into the growth cell in order to change vapor phase stochiometry during the growth. Fluorescent SiC grown using fresh and fully converted tantalum foils contained morphological instabilities leading to lower room temperature photoluminescence intensity while an improved morphology and optical stability was achieved with partly converted tantalum foil. This work reflects the importance of considering the use of Ta foil in sublimation epitaxy regarding the morphological and optical stability in fluorescent silicon carbide.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2013
Keywords
Fluoresecnt Silicon Carbide, Low Off-Axis Substrates, Sublimation Epitaxy
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-88724 (URN)10.4028/www.scientific.net/MSF.740-742.19 (DOI)000319785500005 ()
Conference
9th European Conference on Silicon Carbide & Related Materials (ECSCRM 2012), 2-6 September 2012, Saint-Petersburg, Russia
Available from: 2013-02-14 Created: 2013-02-14 Last updated: 2017-12-06
Jokubavicius, V., Kaiser, M., Hens, P., Wellmann, P., Liljedahl, R., Yakimova, R. & Syväjärvi, M. (2013). Morphological and optical stability in growth of fluorescent SiCon low off-axis substrates. Paper presented at 9th European Conference on Silicon Carbide & Related Materials (ECSCRM 2012), 2-6 September 2012, Saint-Petersburg, Russia.
Open this publication in new window or tab >>Morphological and optical stability in growth of fluorescent SiCon low off-axis substrates
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2013 (English)Conference paper, Published paper (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-87897 (URN)
Conference
9th European Conference on Silicon Carbide & Related Materials (ECSCRM 2012), 2-6 September 2012, Saint-Petersburg, Russia
Available from: 2013-01-27 Created: 2013-01-27 Last updated: 2013-02-11
Schimmel, S., Kaiser, M., Hens, P., Jokubavicius, V., Liljedahl, R., Sun, J., . . . Syväjärvi, M. (2013). Step-flow growth of fluorescent 4H-SiC layers on 4 degree off-axis substrates. In: Alexander A. Lebedev, Sergey Yu. Davydov, Pavel A. Ivanov and Mikhail E. Levinshtein (Ed.), Silicon Carbide and Related Materials 2012: . Paper presented at 9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St. Petersburg, Russia (pp. 185-188). Trans Tech Publications, 740-742
Open this publication in new window or tab >>Step-flow growth of fluorescent 4H-SiC layers on 4 degree off-axis substrates
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2013 (English)In: Silicon Carbide and Related Materials 2012 / [ed] Alexander A. Lebedev, Sergey Yu. Davydov, Pavel A. Ivanov and Mikhail E. Levinshtein, Trans Tech Publications , 2013, Vol. 740-742, p. 185-188Conference paper, Published paper (Refereed)
Abstract [en]

Homoepitaxial layers of fluorescent 4H-SiC were grown on 4 degree off-axis substrates by sublimation epitaxy. Luminescence in the green spectral range was obtained by co-doping with nitrogen and boron utilizing donor-acceptor pair luminescence. This concept opens possibilities to explore green light emitting diodes using a new materials platform.

Place, publisher, year, edition, pages
Trans Tech Publications, 2013
Series
Materials Science Forum, ISSN 0255-5476 ; 740-742
Keywords
Co-Doping, Donor-Acceptor Pair Luminescence, Fluorescent Silicon Carbide, Light Conversion, Sublimation Epitaxy
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-96505 (URN)10.4028/www.scientific.net/MSF.740-742.185 (DOI)000319785500044 ()978-3-03785-624-6 (ISBN)
Conference
9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St. Petersburg, Russia
Available from: 2013-08-23 Created: 2013-08-20 Last updated: 2013-08-30Bibliographically approved
Ou, Y., Jokubavicius, V., Hens, P., Kaiser, M., Wellmann, P., Yakimova, R., . . . Ou, H. (2012). Broadband and omnidirectional light harvesting enhancement of fluorescent SiC. Optics Express, 20(7), 7575-7579
Open this publication in new window or tab >>Broadband and omnidirectional light harvesting enhancement of fluorescent SiC
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2012 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 7, p. 7575-7579Article in journal (Refereed) Published
Abstract [en]

In the present work, antireflective sub-wavelength structures have been fabricated on fluorescent 6H-SiC to enhance the white light extraction efficiency by using the reactive-ion etching method. Broadband and omnidirectional antireflection characteristics show that 6H-SiC with antireflective sub-wavelength structures suppress the average surface reflection significantly from 20.5 % to 1.01 % over a wide spectral range of 390-784 nm. The luminescence intensity of the fluorescent 6H-SiC could be enhanced in the whole emission angle range. It maintains an enhancement larger than 91 % up to the incident angle of 70 degrees, while the largest enhancement of 115.4 % could be obtained at 16 degrees. The antireflective sub-wavelength structures on fluorescent 6H-SiC could also preserve the luminescence spectral profile at a large emission angle by eliminating the Fabry-Perot microcavity interference effect.

Place, publisher, year, edition, pages
Optical Society of America, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-76953 (URN)10.1364/OE.20.007575 (DOI)000302138800075 ()
Note

Funding Agencies|Danish councils for strategic research funding|09-072118|Swedish Energy Agency||Nordic Energy Research||Swedish Research Council|2009-5307|Department of the New Energy||Industrial Technology Development Organization||

Available from: 2012-05-02 Created: 2012-04-27 Last updated: 2017-12-07
Hens, P., Müller, J., Spiecker, E. & Wellmann, P. (2012). Defect structures at the silicon/3C-SiC interface. In: Materials Science Forum Vols 717 - 720. Paper presented at 14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA (pp. 423-426). Trans Tech Publications Inc., 717-720
Open this publication in new window or tab >>Defect structures at the silicon/3C-SiC interface
2012 (English)In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, p. 423-426Conference paper, Published paper (Refereed)
Abstract [en]

In all heteroepitaxial systems the interface between substrate and layer is a crucial point. In this work SEM and TEM studies on the interface between silicon substrate and cubic silicon carbide (3C-SiC) layers obtained by chemical vapor deposition (CVD) are presented. A clear connection between process parameters, like the design of substrate cleaning, and the heating ramp, and resulting defect structures at the substrate-layer interface could be found. Whereas the process step of etching in hot hydrogen for oxide removal is crucial for avoiding the generation of closed voids of type 2, the design of the temperature ramp-up to growth temperature during carbonization influences the interface roughness. Here a fast ramp helps to obtain a flat interface.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keywords
cubic silicon carbide; heteroepitaxy; interface; dislocations; roughness; voids
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87576 (URN)10.4028/www.scientific.net/MSF.717-720.423 (DOI)000309431000100 ()
Conference
14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2013-02-04
Syväjärvi, M., Müller, J., Sun, J., Grivickas, V., Ou, Y., Jokubavicius, V., . . . Ou, H. (2012). Fluorescent SiC as a new material for white LEDs. Physica scripta. T, T148, 014002
Open this publication in new window or tab >>Fluorescent SiC as a new material for white LEDs
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2012 (English)In: Physica scripta. T, ISSN 0281-1847, Vol. T148, p. 014002-Article in journal (Refereed) Published
Abstract [en]

Current III–V-based white light-emitting diodes (LEDs) are available. However, their yellow phosphor converter is not efficient at high currents and includes rare-earth metals, which are becoming scarce. In this paper, we present the growth of a fluorescent silicon carbide material that is obtained by nitrogen and boron doping and that acts as a converter using a semiconductor. The luminescence is obtained at room temperature, and shows a broad luminescence band characteristic of donor-to-acceptor pair recombination. Photoluminescence intensities and carrier lifetimes reflect a sensitivity to nitrogen and boron concentrations. For an LED device, the growth needs to apply low-off-axis substrates. We show by ultra-high-resolution analytical transmission electron microscopy using aberration-corrected electrons that the growth mechanism can be stable and that there is a perfect epitaxial relation from the low-off-axis substrate and the doped layer even when there is step-bunching.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76117 (URN)10.1088/0031-8949/2012/T148/014002 (DOI)000302216000003 ()
Note

funding agencies|Angpanneforeningen Research Foundation||Richerts Foundation||Swedish Energy Agency||Nordic Energy Research||Swedish Research Council| 2009-5307 |Danish Council for Strategic Research| 09-072118 |German Ministry of Education and Research (Federal Ministry of Education and Research)| 03SF0393 |

Available from: 2012-03-27 Created: 2012-03-27 Last updated: 2017-12-07
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