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Monemar, Bo
Alternative names
Publications (10 of 398) Show all publications
Mock, A., Korlacki, R., Briley, C., Darakchieva, V., Monemar, B., Kumagai, Y., . . . Schubert, M. (2017). Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic beta-Ga2O3. Physical Review B, 96(24), Article ID 245205.
Open this publication in new window or tab >>Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic beta-Ga2O3
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, 245205Article in journal (Refereed) Published
Abstract [en]

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic beta-Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-144258 (URN)10.1103/PhysRevB.96.245205 (DOI)000419008900006 ()2-s2.0-85040165150 (Scopus ID)
Note

Funding Agencies|National Science Foundation (NSF) through the Center for Nanohybrid Functional Materials [EPS-1004094]; Nebraska Materials Research Science and Engineering Center [DMR-1420645]; Swedish Research Council [VR2013-5580, VR2016-00889]; Swedish Foundation for Strategic Research (SSF) [FFL12-0181, RIF14-055]; NSF [CMMI 1337856, EAR 1521428]; J. A. Woollam Foundation

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-18Bibliographically approved
Schubert, M., Korlacki, R., Knight, S., Hofmann, T., Schoeche, S., Darakchieva, V., . . . Higashiwaki, M. (2016). Anisotropy, phonon modes, and free charge carrier parameters in monoclinic beta-gallium oxide single crystals. PHYSICAL REVIEW B, 93(12), 125209.
Open this publication in new window or tab >>Anisotropy, phonon modes, and free charge carrier parameters in monoclinic beta-gallium oxide single crystals
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2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 12, 125209- p.Article in journal (Refereed) Published
Abstract [en]

We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and far-infrared active modes. We apply our model approach to monoclinic beta-Ga2O3 single-crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and ((2) over bar 01), are investigated by generalized spectroscopic ellipsometry within infrared and far-infrared spectral regions. We determine the frequency dependence of 4 independent beta-Ga2O3 Cartesian dielectric function tensor elements by matching large sets of experimental data using a point-by-point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infrared and far-infrared active transverse optic phonon modes with A(u) and B-u symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in beta-Ga2O3. We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin-doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in beta-Ga2O3 and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and far-infrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for beta-Ga2O3.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-127273 (URN)10.1103/PhysRevB.93.125209 (DOI)000372412400003 ()
Note

Funding Agencies|National Science Foundation (NSF) through the Center for Nanohybrid Functional Materials [EPS-1004094]; Nebraska Materials Research Science and Engineering Center [DMR-1420645]; Swedish Research Council (VR) [2013-5580, 2010-3848]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486, 2014-04712]; Swedish Foundation for Strategic Research (SSF) [FFL12-0181, RIF14-055]; Linkoping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM) - VR; University of Nebraska-Lincoln; J. A. Woollam Co., Inc.; J. A. Woollam Foundation; [CMMI 1337856]; [EAR 1521428]

Available from: 2016-04-20 Created: 2016-04-19 Last updated: 2016-05-10
Monemar, B., Ohlsson, B. J., Gardner, N. F. & Samuelson, L. (2016). Chapter Seven - Nanowire-Based Visible Light Emitters, Present Status and Outlook. In: Shadi A. Dayeh, Anna Fontcuberta i Morral; Jagadish, Chennupati (Ed.), Semiconductors and Semimetals: Semiconductor Nanowires II: Properties and Applications (pp. 227-271). Elsevier, 94.
Open this publication in new window or tab >>Chapter Seven - Nanowire-Based Visible Light Emitters, Present Status and Outlook
2016 (English)In: Semiconductors and Semimetals: Semiconductor Nanowires II: Properties and Applications / [ed] Shadi A. Dayeh, Anna Fontcuberta i Morral; Jagadish, Chennupati, Elsevier, 2016, Vol. 94, 227-271 p.Chapter in book (Other academic)
Abstract [en]

So far, the semiconductor nanowire research area has mainly delivered results on growth procedures and related material properties. As the development lately has been successful in producing novel nanowire-based structures for optical or electronic applications, the time is ripe to review the device work that has been done and in some cases has produced devices ready for the market. In this chapter, we shall review the specific area of nanowire-based LEDs (NW-LEDs) for visible light, including the application area of “solid state lighting” (SSL). A brief review of the progress in the area of visible light LEDs over the last half century is presented, this also mentions some of the progress made in the planar technology so far. The most successful way of producing white light is still based on the use of phosphors, just like in the present compact fluorescence lamps (CFLs). The reason for this is the high efficiency (external quantum efficiency > 80%) possible at low currents in the violet planar InGaN-based LEDs used to excite the phosphors. These LEDs are presently mainly produced on foreign substrates, leading to a high dislocation density (DD) and a sizeable droop at high injection currents (25–40%). This droop and the down conversion energy loss in the phosphors (20–25%) has motivated the interest for a phosphor-less white light source based on direct mixing of light of different wavelength (such as red, green, and blue; RGB). To be competitive, this solution must be based on highly efficient LEDs for all RGB (red, green, and blue) colors. Since NW-LED structures can be produced basically free of structural defects (even if grown on a foreign substrate), the idea of using the RGB mixing concept for the production of white light sources with an ultimately higher efficiency than for the phosphor-based lamps is a major technical target for a second generation of light sources in the SSL field. Basic concepts behind the design and optical properties of NW-LED structures are discussed in this chapter, with emphasis on the present developments of III-nitride-based structures. The growth procedure relevant for such NW-LED structures is reported in some detail, specifically the core–shell configuration readily produced with metalorganic vapor phase epitaxy (MOVPE). The first generation processing technology for NW-LED structures is briefly described; this is naturally quite different from the established routines for planar LED chips. Experimental data for nitride-based NW-LEDs for blue, green, and even longer wavelengths are given in terms of radiative efficiencies, light outcoupling, droop, and long-term reliability. The experience so far is that for these NW-based emitters, efficiencies can be obtained that are close to those for the corresponding planar LEDs. There are still problems with the reproducibility of the radiative output, as well as a significant droop that would not be expected for m-plane emitters. More work is needed to pinpoint the cause of these problems. Finally, we briefly discuss various applications (also other than white lamps) where the NW-LEDs may have a specific advantage.

Place, publisher, year, edition, pages
Elsevier, 2016
Series
Semiconductors and Semimetals, ISSN 0080-8784 ; 94
Keyword
Nanowires, LEDs, Quantum wells, Visible, Lighting, Display
National Category
Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-123959 (URN)10.1016/bs.semsem.2015.10.002 (DOI)978-0-12-804016-4 (ISBN)
Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-01-21Bibliographically approved
Duc Tran, T., Pozina, G., Amano, H., Monemar, B., Janzén, E. & Hemmingsson, C. (2016). Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy. Physical Review B, 94(4), Article ID 045206.
Open this publication in new window or tab >>Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy
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2016 (English)In: Physical Review B, ISSN 2469-9950, Vol. 94, no 4, 045206Article in journal (Refereed) Published
Abstract [en]

Deep levels in Mg doped GaN have been studied using deep level transient spectroscopyand minority charge carrier transient spectroscopy. Two traps are revealed in the investigatedtemperature range. In the substrate, one electron trap labelled ET1 (EC – 0.158 eV) is observedand in the Mg-doped layer, one hole trap labelled HT1 has been revealed. By varying theelectric field, it is found that the hole trap HT1 exhibits an electric field enhanced hole emissionrate. Using four theoretical models based on 3-dimensional Coulombic Poole-Frenkel effect, 3-dimensional square well Poole-Frenkel effect, phonon assisted tunneling, and 1-dimensionalCoulombic Poole-Frenkel effect including phonon assisted tunneling, the experimental data arefitted in order to justify the field enhanced emission process. It is found that the 1-dimensionalCoulombic Poole-Frenkel model including phonon assisted tunneling is consistent with theexperimental data. Since the trap exhibits Poole-Frenkel effect, we suggest it is acceptor like.From the theoretical model, the zero field activation energy of HT1 and an estimate of the holecapture cross section have been determined as Ev+0.57 eV and 1.9x10-15 cm2, respectively.Since the level is only observed in Mg-doped material, it is suggested that the trap can beassociated with a Mg related defect.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121705 (URN)10.1103/PhysRevB.94.045206 (DOI)000381484500007 ()
Note

Funding agenices: Swedish Research Council [621-2010-3850]; Swedish Energy Agency [38338-1]

Vid tiden för disputation förelåg publikationen endast som manuskript

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2016-09-26Bibliographically approved
Duc Tran, T., Pozina, G., Nguyen, T. S., Kordina, O., Janzén, E., Ohshima, T. & Hemmingsson, C. (2016). Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy. Journal of Applied Physics, 119(9).
Open this publication in new window or tab >>Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 9Article in journal (Refereed) Published
Abstract [en]

By minority carrier transient spectroscopy on as-grown n-type bulk GaN produced by halide vapor phase epitaxy (HVPE) one hole trap labelled H1 (EV + 0.34 eV) has been detected. After 2 MeV-energy electron irradiation, the concentration of H1 increases and at fluences higher than 5×1014 cm-2, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (EC - 0.12 eV) and T2 (EC - 0.23 eV) increases. By studying the increase of the concentration versus electron irradiation fluences, the introduction rate of T1 and T2 using 2 MeV-energy electrons was determined to 7X10-3 cm-1 and 0.9 cm-1, respectively. Due to the low introduction rate of T1 and the low threading dislocation density in the HVPE bulk GaN material, it is suggested that the defect is associated with a primary defect decorating extended structural defects. The high introduction rate of the trap H1 suggests that the H1 defect is associated with a primary intrinsic defect or a complex.

Keyword
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121709 (URN)10.1063/1.4943029 (DOI)000372351900075 ()
Note

Funding agencies:  Swedish Research Council (VR); Swedish Energy Agency

Vid tiden för disputation förelåg publikationen som manuskript

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2017-12-01Bibliographically approved
Duc Tran, T., Pozina, G., Nguyen, T. S., Ohshima, T., Janzén, E. & Hemmingsson, C. (2016). Electronic properties of defects in high-fluence electron irradiated bulk GaN. Physica status solidi. B, Basic research, 253(3), 521-526.
Open this publication in new window or tab >>Electronic properties of defects in high-fluence electron irradiated bulk GaN
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2016 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 253, no 3, 521-526 p.Article in journal (Refereed) Published
Abstract [en]

Using deep level transient spectroscopy, deep levels and capture cross sections of defects introduced by high-fluence electron irradiation of thick halide vapour phase epitaxy grown GaN has been studied. After irradiation with 2 MeV electrons to a high-fluence of 5×1016 cm-2, four deep trap levels, labelled T1 (EC – 0.13 eV), T2 (EC – 0.18 eV), T3 (EC – 0.26 eV) T4 and a broad band of peaks consisting of at least two levels could be observed. These defects, except T1 and T3, were annealed out after annealing at 650 K for 2 hours. The capture cross section is found to be temperature independent for T2 and T3, while T1 shows an decresing capture cross section with increasing temperature, suggesting that electron capturing to this deep level is governed by a cascade capturing process.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keyword
Deep level, GaN, DLTS, irradiation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121707 (URN)10.1002/pssb.201552521 (DOI)000371634800018 ()
Note

Funding agencies: Swedish Research Council (VR); Swedish Energy Agency

Available from: 2015-10-02 Created: 2015-10-02 Last updated: 2017-12-01Bibliographically approved
Tojo, S., Yamamoto, R., Tanaka, R., Tu Thieu, Q., Togashi, R., Nagashima, T., . . . Kumagai, Y. (2016). Influence of high-temperature processing on the surface properties of bulk AlN substrates. Journal of Crystal Growth, 446, 33-38.
Open this publication in new window or tab >>Influence of high-temperature processing on the surface properties of bulk AlN substrates
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2016 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 446, 33-38 p.Article in journal (Refereed) Published
Abstract [en]

Deep-level luminescence at 3.3 eV related to the presence of Al vacancies (V-Al) was observed in room temperature photoluminescence (RT-PL) spectra of homoepitaxial AlN layers grown at 1450 degrees C by hydride vapor-phase epitaxy (HVPE) and cooled to RT in a mixture of H-2 and N-2 with added NH3. However, this luminescence disappeared after removing the near surface layer of AlN by polishing. In addition, the deep-level luminescence was not observed when the post-growth cooling of AlN was conducted without NH3. Secondary ion mass spectrometry (SIMS) studies revealed that although the point defect density of the interior of the AlN layers remained low, the near surface layer cooled in the presence of NH3 was contaminated by Si impurities due to both suppression of the surface decomposition by the added NH3 and volatilization of Si by decomposition of the quartz reactor walls at high temperatures. The deep-level luminescence reappeared after the polished AlN wafers were heated in presence of NH3 at temperatures above 1400 degrees C. The surface contamination by Si is thought to generate V-Al near the surface by lowering their formation energy due to the Fermi level effect, resulting in deep-level luminescence at 3.3 eV caused by the shallow donor (Si) to V-Al transition. (C) 2016 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2016
Keyword
Impurities; Point defects; Hydride vapor phase epitaxy; Nitrides; Quartz; Semiconducting aluminum compounds
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-129469 (URN)10.1016/j.jcrysgro.2016.04.030 (DOI)000376444100005 ()
Note

Funding Agencies|Adaptable and Seamless Technology Transfer Program under the Japan Science and Technology Agency [AS2525010J]; Japan Society for the Promotion of Science [15H03555]

Available from: 2016-06-21 Created: 2016-06-20 Last updated: 2017-11-28
Hirasaki, T., Hasegawa, T., Meguro, M., Thieu, Q. T., Murakami, H., Kumagai, Y., . . . Koukitu, A. (2016). Investigation of NH3 input partial pressure for N-polarity InGaN growth on GaN substrates by tri-halide vapor phase epitaxy. Paper presented at 6th International Symposium on Growth of III-Nitrides (ISGN). Japanese Journal of Applied Physics, 55(5), 05FA01.
Open this publication in new window or tab >>Investigation of NH3 input partial pressure for N-polarity InGaN growth on GaN substrates by tri-halide vapor phase epitaxy
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2016 (English)In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 55, no 5, 05FA01- p.Article in journal (Refereed) Published
Abstract [en]

The influence of NH3 input partial pressure on N-polarity InGaN grown by tri-halide vapor phase epitaxy was investigated. It was found that surface morphology, solid composition and optical properties were affected by NH3 input partial pressure. As shown in thermodynamic analyses, the indium content increased due to an increase in the driving force for InN deposition caused by increased NH3 input partial pressure. In addition, the deep level emission around 2.1 eV in photoluminescence measurements drastically decreased at higher NH3 input partial pressures. Ab initio calculations and subsequent secondary ion mass spectrometry measurements suggested the reduction of metal-vacancies and/or carbon impurity incorporation in the InGaN layers. (C) 2016 The Japan Society of Applied Physics

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-128950 (URN)10.7567/JJAP.55.05FA01 (DOI)000374697600002 ()
Conference
6th International Symposium on Growth of III-Nitrides (ISGN)
Available from: 2016-06-09 Created: 2016-06-07 Last updated: 2017-11-30
Higashiwaki, M., Konishi, K., Sasaki, K., Goto, K., Nomura, K., Quang Tu Thieu; Togashi, R., . . . Yamakoshi, S. (2016). Temperature-dependent capacitance-voltage and current-voltage characteristics of Pt/Ga2O3 (001) Schottky barrier diodes fabricated on n(-)-Ga2O3 drift layers grown by halide vapor phase epitaxy. Applied Physics Letters, 108(13), 133503.
Open this publication in new window or tab >>Temperature-dependent capacitance-voltage and current-voltage characteristics of Pt/Ga2O3 (001) Schottky barrier diodes fabricated on n(-)-Ga2O3 drift layers grown by halide vapor phase epitaxy
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2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 13, 133503- p.Article in journal (Refereed) Published
Abstract [en]

We investigated the temperature-dependent electrical properties of Pt/Ga2O3 Schottky barrier diodes (SBDs) fabricated on n(-)-Ga2O3 drift layers grown on single-crystal n(+)-Ga2O3 (001) substrates by halide vapor phase epitaxy. In an operating temperature range from 21 degrees C to 200 degrees C, the Pt/Ga2O3 (001) Schottky contact exhibited a zero-bias barrier height of 1.09-1.15 eV with a constant near-unity ideality factor. The current-voltage characteristics of the SBDs were well-modeled by thermionic emission in the forward regime and thermionic field emission in the reverse regime over the entire temperature range. (C) 2016 AIP Publishing LLC.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-127567 (URN)10.1063/1.4945267 (DOI)000373601400041 ()
Note

Funding Agencies|Council for Science, Technology and Innovation (CSTI); NEDO

Available from: 2016-05-04 Created: 2016-05-03 Last updated: 2017-11-30
Khromov, S., Persson, P. O., Wang, X., Yoshikawa, A., Monemar, B., Rosén, J., . . . Darakchieva, V. (2015). Correlation between switching to n-type conductivity and structural defects in highly Mg-doped InN. Applied Physics Letters, 106(23), Article ID 232102.
Open this publication in new window or tab >>Correlation between switching to n-type conductivity and structural defects in highly Mg-doped InN
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 23, 232102Article in journal (Refereed) Published
Abstract [en]

The effect of Mg doping on the microstructure of InN epitaxial films in relation to their free-charge carrier properties has been investigated by transmission electron microscopy (TEM) and aberration corrected scanning TEM. We observe a direct correlation between Mg concentration and the formation of stacking faults. The threading dislocation density is found to be independent of Mg concentration. The critical Mg concentration for the on-set of stacking faults formation is determined and found to correlate with the switch from p- to n-type conductivity in InN. Potential mechanisms involving stacking faults and point defect complexes are invoked in order to explain the observed conductivity reversal. Finally, the stacking faults are structurally determined and their role in the reduction of the free electron mobility in highly doped InN: Mg is discussed. (C) 2015 AIP Publishing LLC.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-120046 (URN)10.1063/1.4922301 (DOI)000356170900016 ()
Note

Funding Agencies|Swedish Research Council (VR) [2008-405, 2012-4359, 2013-5580, 642-2013-8020]; ERC [258509]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486]; Swedish Foundation for Strategic Research (SSF) [FFL12-0181]; National Basic Research Program of China [2012CB619300]; National Natural Science Foundation of China [61225019, 61376060]

Available from: 2015-07-06 Created: 2015-07-06 Last updated: 2017-12-04
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