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Bergman, J. Peder
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Publications (10 of 190) Show all publications
Seed Ahmed, H. A., Swart, H. C., Bergman, P. & Kroon, R. E. (2016). Concentration quenching of Eu2+ doped Ca2BO3Cl. Materials research bulletin, 75, 47-50
Open this publication in new window or tab >>Concentration quenching of Eu2+ doped Ca2BO3Cl
2016 (English)In: Materials research bulletin, ISSN 0025-5408, E-ISSN 1873-4227, Vol. 75, p. 47-50Article in journal (Refereed) Published
Abstract [en]

With the aim of determining the concentration quenching mechanism of Eu2+ doped Ca2BO3Cl, a series of phosphors with a varied Eu2+ concentration (Ca2-xBO3Cl:xEu(2+)) was synthesized by the solid state reaction method. The phase structure was determined by X-ray diffraction. Photoluminescence (PL) measurements showed broad excitation and emission signatures of the allowed f-d transition of Eu2+ ions. The PL emission intensity was found to be increased by increasing the concentration of Eu2+ ions up to x=0.03 and then decreased as a result of the concentration quenching effect. The lifetime of the emission from the Eu2+ ions was measured and the decrease in the lifetime with increasing Eu2+ concentration confirmed that non-radiative energy transfer occurred between Eu2+ ions. From the luminescence data, the value of the critical transfer distance was calculated as 1.5 nm and the corresponding concentration quenching mechanism was verified to be a dipole-dipole interaction. (C) 2015 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2016
Keywords
Optical materials; X-ray diffraction; Luminescence; Optical properties; Phosphors
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-124619 (URN)10.1016/j.materresbull.2015.11.024 (DOI)000368220300008 ()
Note

Funding Agencies|South African Research Chairs Initiative of the Department of Science and Technology; National Research Foundation of South Africa; University of the Free State

Available from: 2016-02-09 Created: 2016-02-08 Last updated: 2017-11-30
Yagoub, M. Y., Swart, H. C., Bergman, P. & Coetsee, E. (2016). Enhanced Pr3+ photoluminescence by energy transfer in SrF2:Eu2+, Pr3+ phosphor. AIP Advances, 6(2), 025204
Open this publication in new window or tab >>Enhanced Pr3+ photoluminescence by energy transfer in SrF2:Eu2+, Pr3+ phosphor
2016 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 6, no 2, p. 025204-Article in journal (Refereed) Published
Abstract [en]

Efficient energy transfer was demonstrated in the SrF2:Eu2+, Pr3+ phosphor synthesized by the co-precipitation method. Results obtained with X-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray spectroscopy (XPS), photoluminescence (PL) and decay curves proposed the UV-Vis energy transfer process. The energy transfer process between the Eu2+ and Pr3+ ions in SrF2 was investigated to evaluate the potential of the Eu2+ ion as a sensitizer for the Pr3+ ion. The results proposed that Eu2+ could be a good sensitizer for absorbing the UV photons and efficiently enhancing the Pr3+ emission intensity. The energy transfer process was effective until concentration quenching for the Pr3+ ions occurred. The concentration quenching was attributed to cross-relaxation between the Pr3+ ions. (C) 2016 Author(s).

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-126843 (URN)10.1063/1.4941833 (DOI)000371739000055 ()
Note

Funding Agencies|South African Research Chairs Initiative of the Department of Science and Technology; National Research Foundation of South Africa; National Research Foundation (NRF); Cluster program of the University of the Free State

Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2017-11-30
Salemi, A., Elahipanah, H., Buono, B., Hallen, A., Ul-Hassan, J., Bergman, P., . . . Ostling, M. (2015). Conductivity Modulated On-axis 4H-SiC 10+kV PiN Diodes. In: 2015 IEEE 27TH INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES and ICS (ISPSD): . Paper presented at 27th International Symposium on Power Semiconductor Devices and ICs (ISPSD) (pp. 269-272). IEEE
Open this publication in new window or tab >>Conductivity Modulated On-axis 4H-SiC 10+kV PiN Diodes
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2015 (English)In: 2015 IEEE 27TH INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES and ICS (ISPSD), IEEE , 2015, p. 269-272Conference paper, Published paper (Refereed)
Abstract [en]

Degradation-free ultrahigh-voltage (> 10 kV) PiN diodes using on-axis 4H-SiC with low forward voltage drop (V-F = 3.3 V at 100 A/cm(2)) and low differential on-resistance (R-ON = 3.4 m Omega.cm(2)) are fabricated, measured, and analyzed by device simulation. The devices show stable on-state characteristics over a broad temperature range up to 300 degrees C. They show no breakdown up to 10 kV, i.e., the highest blocking capability for 4H-SiC devices using on-axis to date. The minority carrier lifetime (tau(P)) is measured after epitaxial growth by time resolved photoluminescence (TRPL) technique at room temperature. The tau(P) is measured again after device fabrication by open circuit voltage decay (OCVD) up to 500 K.

Place, publisher, year, edition, pages
IEEE, 2015
Series
Proceedings of the International Symposium on Power Semiconductor Devices & ICs, ISSN 1063-6854
Keywords
On-axis 4H-SiC; PiN diode; ultrahigh-voltage; lifetime enhancement; V-F; on-resistance; OCVD; breakdown voltage; bipolar degradation-free
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-126278 (URN)000370717300066 ()978-1-4799-6261-7 (ISBN)
Conference
27th International Symposium on Power Semiconductor Devices and ICs (ISPSD)
Available from: 2016-03-21 Created: 2016-03-21 Last updated: 2016-03-21
Lilja, L., Ul-Hassan, J., Janzén, E. & Bergman, P. (2015). In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates. Physica status solidi. B, Basic research, 252(6), 1319-1324
Open this publication in new window or tab >>In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates
2015 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, p. 1319-1324Article in journal (Refereed) Published
Abstract [en]

4H-SiC epilayers were grown on 2 degrees off-cut substrates using standard silane/propane chemistry, with the aim of characterizing in-grown stacking faults. The stacking faults were analyzed with low temperature photoluminescence spectroscopy, room temperature photoluminescence mappings, room temperature cathodoluminescence and synchrotron white beam X-ray topography. At least three different types of in-grown stacking faults were observed, including double Shockley stacking faults, triple Shockley stacking faults and bar-shaped stacking faults. Those stacking faults are all previously found in 4 degrees and 8 degrees off-cut epilayers; however, the geometrical size is larger in epilayers grown on 2 degrees off-cut substrates due to lower off-cut angle. The stacking faults were formed close to the epilayer/substrate interface during the epitaxial growth. (C) 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2015
Keywords
chemical vapor deposition; epitaxy; photoluminescence; SiC; stacking faults
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-120065 (URN)10.1002/pssb.201451710 (DOI)000355756200018 ()
Note

Funding Agencies|Swedish Research Council (VR); Advanced Functional Materials (AFM); Swedish Foundation for Strategic Research (SSF)

Available from: 2015-07-06 Created: 2015-07-06 Last updated: 2017-12-04
Yagoub, M. Y. A., Swart, H. C., Noto, L. L., Bergman, P. & Coetsee, E. (2015). Surface Characterization and Photoluminescence Properties of Ce3+, Eu Co-Doped SrF2 Nanophosphor. Materials, 8(5), 2361-2375
Open this publication in new window or tab >>Surface Characterization and Photoluminescence Properties of Ce3+, Eu Co-Doped SrF2 Nanophosphor
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2015 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 8, no 5, p. 2361-2375Article in journal (Refereed) Published
Abstract [en]

SrF2:Eu,Ce3+ nanophosphors were successfully synthesized by the hydrothermal method during down-shifting investigations for solar cell applications. The phosphors were characterized by X-ray diffraction (XRD), scanning Auger nanoprobe, time of flight-secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. XRD showed that the crystallite size calculated with Scherrers equation was in the nanometre scale. XPS confirmed the formation of the matrix and the presence of the dopants in the SrF2 host. The PL of the nanophosphor samples were studied using different excitation sources. The phenomenon of energy transfer from Ce3+ to Eu2+ has been demonstrated.

Place, publisher, year, edition, pages
MDPI, 2015
Keywords
SrF2; cerium; TOF-SIMS; XPS; shake-down; energy transfer
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-120292 (URN)10.3390/ma8052361 (DOI)000356879100022 ()
Note

Funding Agencies|South African Research Chairs Initiative of the Department of Science and Technology; National Research Foundation of South Africa; National Research Foundation (NRF); University of the Free State

Available from: 2015-07-24 Created: 2015-07-24 Last updated: 2017-12-04
Shevchenko, E. A., Toropov, A. A., Nechaev, D. V., Jmerik, V. N., Shubina, T. V., Ivanov, S. V., . . . Monemar, B. (2014). AlGaN Quantum Well Heterostructures for Mid-Ultraviolet Emitters with Improved Room Temperature Quantum Efficiency. Paper presented at 43rd Jaszowiec International School and Conference on the Physics of Semiconductors. Acta Physica Polonica. A, 126(5), 1140-1142
Open this publication in new window or tab >>AlGaN Quantum Well Heterostructures for Mid-Ultraviolet Emitters with Improved Room Temperature Quantum Efficiency
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2014 (English)In: Acta Physica Polonica. A, ISSN 0587-4246, E-ISSN 1898-794X, Vol. 126, no 5, p. 1140-1142Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
POLISH ACAD SCIENCES INST PHYSICS, 2014
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-113203 (URN)10.12693/APhysPolA.126.1140 (DOI)000346069100026 ()2-s2.0-84916894578 (Scopus ID)
Conference
43rd Jaszowiec International School and Conference on the Physics of Semiconductors
Available from: 2015-01-13 Created: 2015-01-12 Last updated: 2017-12-05
Booker, I. D., Ul Hassan, J., Lilja, L., Beyer, F., Karhu, R., Bergman, J. P., . . . Janzén, E. (2014). Carrier Lifetime Controlling Defects Z(1/2) and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC. Crystal Growth & Design, 14(8), 4104-4110
Open this publication in new window or tab >>Carrier Lifetime Controlling Defects Z(1/2) and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC
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2014 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 8, p. 4104-4110Article in journal (Refereed) Published
Abstract [en]

4H-SiC epilayers grown by standard and chlorinated chemistry were analyzed for their minority carrier lifetime and deep level recombination centers using time-resolved photoluminescence (TRPL) and standard deep level transient spectroscopy (DLTS). Next to the well-known Z(1/2) deep level a second effective lifetime killer, RB1 (activation energy 1.05 eV, electron capture cross section 2 x 10(-16) cm(2), suggested hole capture cross section (5 +/- 2) x 10(-15) cm(2)), is detected in chloride chemistry grown epilayers. Junction-DLTS and bulk recombination simulations are used to confirm the lifetime killing properties of this level. The measured RB1 concentration appears to be a function of the iron-related Fe1 level concentration, which is unintentionally introduced via the corrosion of reactor steel parts by the chlorinated chemistry. Reactor design and the growth zone temperature profile are thought to enable the formation of RB1 in the presence of iron contamination under conditions otherwise optimal for growth of material with very low Z(1/2) concentrations. The RB1 defect is either an intrinsic defect similar to RD1/2 or EH5 or a complex involving iron. Control of these corrosion issues allows the growth of material at a high growth rate and with high minority carrier lifetime based on Z(1/2) as the only bulk recombination center.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-110278 (URN)10.1021/cg5007154 (DOI)000340080400049 ()
Note

Funding Agencies|The Swedish Energy Agency; Swedish Research Council (VR); Swedish Foundation for Strategic Research (SSF); LG Innotek

Available from: 2014-09-05 Created: 2014-09-05 Last updated: 2017-12-05Bibliographically approved
Kallinger, B., Rommel, M., Lilja, L., ul-Hassan, J., Booker, I. D., Janzén, E. & Bergman, P. (2014). Comparison of carrier lifetime measurements and mapping in 4H SIC using time resolved photoluminescence and μ-PCD. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials, ICSCRM 2013 (pp. 301-304). Stafa-Zurich, Switzerland: Trans Tech Publications, 778-780
Open this publication in new window or tab >>Comparison of carrier lifetime measurements and mapping in 4H SIC using time resolved photoluminescence and μ-PCD
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2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Stafa-Zurich, Switzerland: Trans Tech Publications , 2014, Vol. 778-780, p. 301-304Conference paper, Published paper (Refereed)
Abstract [en]

Carrier lifetime measurements and wafer mappings have been done on several different 4H SiC epiwafers to compare two different measurement techniques, time-resolved photoluminescence and microwave induced photoconductivity decay. The absolute values of the decay time differ by a factor of two, as expected from recombination and measurement theory. Variations within each wafer are comparable with the two techniques. Both techniques are shown to be sensitive to substrate quality and distribution of extended defects.

Place, publisher, year, edition, pages
Stafa-Zurich, Switzerland: Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 0255-5476 ; vol 778-780
Keywords
Carrier lifetime; Photoluminescence; Silicon carbide; μ-PCD
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-110541 (URN)10.4028/www.scientific.net/MSF.778-780.301 (DOI)000336634100071 ()2-s2.0-84896069395 (Scopus ID)9783038350101 (ISBN)
Conference
15th International Conference on Silicon Carbide and Related Materials, ICSCRM 2013
Available from: 2014-09-15 Created: 2014-09-12 Last updated: 2014-09-15
Salemi, A., Buono, B., Hallen, A., ul-Hassan, J., Bergman, P., Zetterling, C. & Östling, M. (2014). Fabrication and design of 10 kV PiN diodes using on-axis 4H-SiC. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials, ICSCRM 2013 (pp. 836-840). Trans Tech Publications, 778-780
Open this publication in new window or tab >>Fabrication and design of 10 kV PiN diodes using on-axis 4H-SiC
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2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 836-840Conference paper, Published paper (Refereed)
Abstract [en]

10 kV PiN diodes using on-axis 4H-SiC were designed, fabricated, and measured. A lifetime enhancement procedure was done by carbon implantation followed by high temperature annealing to increase lifetime to above 2 μs. The device simulation software Sentaurus TCAD has been used in order to optimize the diode. All fabricated diodes are fully functional and have a VF of 3.3 V at 100 A/cm2 at 25C, which was decreased to 3.0 V at 300C.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 0255-5476 ; Vol 778-780
Keywords
Lifetime enhancement; On-axis 4h-SiC; PiN diode
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-110543 (URN)10.4028/www.scientific.net/MSF.778-780.836 (DOI)000336634100198 ()2-s2.0-84896089454 (Scopus ID)9783038350101 (ISBN)
Conference
15th International Conference on Silicon Carbide and Related Materials, ICSCRM 2013
Available from: 2014-09-15 Created: 2014-09-12 Last updated: 2014-09-15
Ul-Hassan, J., Bae, H., Lilja, L., Farkas, I., Kim, I., Stenberg, P., . . . Janzén, E. (2014). Fast growth rate epitaxy on 4((degrees)under-bar) off-cut 4-inch diameter 4H-SiC wafers. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials (ICSCRM), Miyazaki, Japan, 29 Sptember - 4 October 2013 (pp. 179-182). Trans Tech Publications, 778-780
Open this publication in new window or tab >>Fast growth rate epitaxy on 4((degrees)under-bar) off-cut 4-inch diameter 4H-SiC wafers
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2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 179-182Conference paper, Published paper (Refereed)
Abstract [en]

We report the development of over 100 mu m/h growth rate process on 4-inch diameter wafers using chlorinated growth. The optimized growth process has shown extremely smooth epilayers completely free of surface step-bunching with very low surface defect density, high uniformity in thickness and doping and high run to run reproducibility in growth rate, controlled doping and defect density.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keywords
Fast epitaxial growth; high growth rate; chlorinated growth; atomic force microscopy
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-108193 (URN)10.4028/www.scientific.net/MSF.778-780.179 (DOI)000336634100042 ()
Conference
15th International Conference on Silicon Carbide and Related Materials (ICSCRM), Miyazaki, Japan, 29 Sptember - 4 October 2013
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2016-06-02Bibliographically approved
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