liu.seSearch for publications in DiVA
Change search
Refine search result
1 - 17 of 17
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Armakavicius, Nerijus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Knight, Sean Robert
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kuhne, Philipp
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tran, Dat
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Richter, Steffen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Papamichail, Alexis
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stokey, Megan
    Univ Nebraska Lincoln, NE 68588 USA.
    Sorensen, Preston
    Univ Nebraska Lincoln, NE 68588 USA.
    Kilic, Ufuk
    Univ Nebraska Lincoln, NE 68588 USA.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden; Univ Nebraska Lincoln, NE 68588 USA.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Electron effective mass in GaN revisited: New insights from terahertz and mid-infrared optical Hall effect2024In: APL Materials, E-ISSN 2166-532X, Vol. 12, no 2, article id 021114Article in journal (Refereed)
    Abstract [en]

    Electron effective mass is a fundamental material parameter defining the free charge carrier transport properties, but it is very challenging to be experimentally determined at high temperatures relevant to device operation. In this work, we obtain the electron effective mass parameters in a Si-doped GaN bulk substrate and epitaxial layers from terahertz (THz) and mid-infrared (MIR) optical Hall effect (OHE) measurements in the temperature range of 38-340 K. The OHE data are analyzed using the well-accepted Drude model to account for the free charge carrier contributions. A strong temperature dependence of the electron effective mass parameter in both bulk and epitaxial GaN with values ranging from (0.18 +/- 0.02) m(0) to (0.34 +/- 0.01) m(0) at a low temperature (38 K) and room temperature, respectively, is obtained from the THz OHE analysis. The observed effective mass enhancement with temperature is evaluated and discussed in view of conduction band nonparabolicity, polaron effect, strain, and deviations from the classical Drude behavior. On the other hand, the electron effective mass parameter determined by MIR OHE is found to be temperature independent with a value of (0.200 +/- 0.002) m(0). A possible explanation for the different findings from THz OHE and MIR OHE is proposed. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

  • 2.
    Delgado Carrascon, Rosalia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tran, Dat Quoc
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sukkaew, Pitsiri
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Mock, Alyssa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Naval Res Lab, DC 20375 USA.
    Ciechonski, Rafal
    Hexagem AB, Sweden.
    Ohlsson, Jonas
    Hexagem AB, Sweden; Lund Univ, Sweden.
    Zhu, Yadan
    Lund Univ, Sweden.
    Hultin, Olof
    Lund Univ, Sweden.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Samuelson, Lars
    Lund Univ, Sweden.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Optimization of GaN Nanowires Reformation Process by Metalorganic Chemical Vapor Deposition for Device-Quality GaN Templates2020In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 257, no 4, article id 1900581Article in journal (Refereed)
    Abstract [en]

    Herein, the potential of reformed GaN nanowires (NWs) fabricated by metalorganic chemical vapor deposition (MOCVD) for device-quality low-defect density templates and low-cost alternative to bulk GaN substrates is demonstrated. The effects of epilayer thickness and NW reformation conditions on the crystalline quality and thermal conductivity of the subsequent GaN epilayers are investigated. Smooth surfaces with atomically step-like morphologies with no spirals are achieved for GaN epilayers on the reformed NW templates, indicating step-flow growth mode. It is further found that annealing of the NWs at a temperature of 1030 degrees C in the presence of NH3 and H-2, followed by a coalescence done at the same temperature under planar growth conditions, leads to the most efficient screw dislocation density reduction by nearly an order of magnitude. At these optimized conditions, the growth takes place in a layer-by-layer fashion, producing a smooth surface with a root mean square (RMS) roughness of 0.12 nm. The highest thermal conductivity of k = 206 W m(-1) K-1, approaching the respective value of bulk GaN, is obtained for the optimized 2 mu m-thick GaN layer. The thermal conductivity results are further discussed in terms of the phonon-dislocation and the phonon-boundary scattering.

  • 3.
    Gogova, Daniela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ghezellou, Misagh
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tran, Dat Q.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Richter, Steffen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Solid State Physics and NanoLund, Lund University, P. O. Box 118, 221 00 Lund, Sweden.
    Papamichail, Alexis
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Persson, Axel R.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Kordina, Olof
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hilfiker, Matthew
    Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
    Paskov, Plamen P.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Solid State Physics and NanoLund, Lund University, P. O. Box 118, 221 00 Lund, Sweden.
    Epitaxial growth of β-Ga2O3 by hot-wall MOCVD2022In: AIP Advances, E-ISSN 2158-3226, Vol. 12, no 5, article id 055022Article in journal (Refereed)
    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.

  • 4.
    Gogova-Petrova, Daniela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tran, Dat
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Vines, L.
    Univ Oslo, Norway.
    Schubert, M.
    Lund Univ, Sweden; Univ Nebraska, NE 68588 USA.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    High crystalline quality homoepitaxial Si-doped β-Ga2O3(010) layers with reduced structural anisotropy grown by hot-wall MOCVD2024In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 42, no 2, article id 022708Article in journal (Refereed)
    Abstract [en]

    A new growth approach, based on the hot-wall metalorganic chemical vapor deposition concept, is developed for high-quality homoepitaxial growth of Si-doped single-crystalline beta-Ga2O3 layers on (010)-oriented native substrates. Substrate annealing in argon atmosphere for 1 min at temperatures below 600 degrees C is proposed for the formation of epi-ready surfaces as a cost-effective alternative to the traditionally employed annealing process in oxygen-containing atmosphere with a time duration of 1 h at about 1000 degrees C. It is shown that the on-axis rocking curve widths exhibit anisotropic dependence on the azimuth angle with minima for in-plane direction parallel to the [001] and maximum for the [100] for both substrate and layer. The homoepitaxial layers are demonstrated to have excellent structural properties with a beta-Ga2O3(020) rocking curve full-widths at half-maximum as low as 11 arc sec, which is lower than the corresponding one for the substrates (19 arc sec), even for highly Si-doped (low 1019 cm -3 range) layers. Furthermore, the structural anisotropy in the layer is substantially reduced with respect to the substrate. Very smooth surface morphology of the epilayers with a root mean square roughness value of 0.6 nm over a 5 x 5 mu m(2) area is achieved along with a high electron mobility of 69 cm 2 V -1 s -1 at a free carrier concentration n = 1.9 x 10(19) cm -3. These values compare well with state-of-the-art parameters reported in the literature for beta-Ga2O3(010) homoepitaxial layers with respective Si doping levels. Thermal conductivity of 17.4 Wm(-1)K(-1) is determined along the [010] direction for the homoepitaxial layers at 300 K, which approaches the respective value of bulk crystal (20.6 Wm(-1)K(-1)). This result is explained by a weak boundary effect and a low dislocation density in the homoepitaxial layers.

  • 5.
    Kuhne, Philipp
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Armakavicius, Nerijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Papamichail, Alexis
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tran, Dat
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Nebraska Lincoln, NE 68588 USA.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Enhancement of 2DEG effective mass in AlN/Al0.78Ga0.22N high electron mobility transistor structure determined by THz optical Hall effect2022In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 120, no 25, article id 253102Article in journal (Refereed)
    Abstract [en]

    We report on the free charge carrier properties of a two-dimensional electron gas (2DEG) in an AlN/AlxGa1-xN high electron mobility transistor structure with a high aluminum content (x = 0.78). The 2DEG sheet density N s = ( 7.3 +/- 0.7 ) x 10 12 cm(-2), sheet mobility mu s = ( 270 +/- 40 ) cm(2)/(Vs), sheet resistance R- s = ( 3200 +/- 500 ) omega/ ?, and effective mass m( eff) = ( 0.63 +/- 0.04 ) m( 0) at low temperatures ( T = 5 K ) are determined by terahertz (THz) optical Hall effect measurements. The experimental 2DEG mobility in the channel is found within the expected range, and the sheet carrier density is in good agreement with self-consistent Poisson-Schrodinger calculations. However, a significant increase in the effective mass of 2DEG electrons at low temperatures is found in comparison with the respective value in bulk Al0.78Ga22N ( m( eff) = 0.334 m( 0)). Possible mechanisms for the enhanced 2DEG effective mass parameter are discussed and quantified using self-consistent Poisson-Schrodinger calculations .Published under an exclusive license by AIP Publishing.

    Download full text (pdf)
    fulltext
  • 6.
    Sundarapandian, Balasubramanian
    et al.
    Fraunhofer Inst Appl Solid State Phys, Germany.
    Tran, Dat
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kirste, Lutz
    Fraunhofer Inst Appl Solid State Phys, Germany.
    Stranak, Patrik
    Fraunhofer Inst Appl Solid State Phys, Germany.
    Graff, Andreas
    Fraunhofer Inst Microstruct Mat & Syst, Germany.
    Prescher, Mario
    Fraunhofer Inst Appl Solid State Phys, Germany.
    Nair, Akash
    Fraunhofer Inst Appl Solid State Phys, Germany.
    Raghuwanshi, Mohit
    Fraunhofer Inst Appl Solid State Phys, Germany.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ambacher, Oliver
    Univ Freiburg, Germany.
    Comparison of aluminum nitride thin films prepared by magnetron sputter epitaxy in nitrogen and ammonia atmosphere2024In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 124, no 18, article id 182101Article in journal (Refereed)
    Abstract [en]

    Wurtzite-type aluminum nitride (AlN) thin films exhibiting high thermal conductivity, large grain size, and low surface roughness are desired for both bulk acoustic wave and surface acoustic wave resonators. In this work, we use ammonia (NH3) assisted reactive sputter deposition of AlN to significantly improve these properties. The study shows a systematic change in the structural, thermal, and morphological properties of AlN grown in nitrogen (N2) and N2 + NH3 atmosphere. The study demonstrates that NH3 assisted AlN sputtering facilitates 2D growth. In addition, the study presents a growth model relating the 2D growth to improve the mobility of aluminum (Al) and nitrogen (N) ad-atoms in NH3 atmosphere. Consequently, the thermal conductivity and roughness improve by approximate to 76%, and approximate to 35%, while the grain size increases by approximate to 78%.

  • 7. Order onlineBuy this publication >>
    Tran, Dat
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Thermal conductivity of AlXGa1-XN and β-Ga2O3 semiconductors2021Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    For the high-power (HP) electronic applications the existing Si-based devices have reached the performance limits governed by the material properties. Hence the device innovation itself is unable to enhance the overall performance. GaN, a semiconductor with wide bandgap, high critical breakdown field, and high electronic saturation velocity is regarded as an alternative of Si. The material properties of GaN make it very suitable for fast-switching HP electronic devices and contribute to the fast growing of GaN technology. The state-of-the-art GaN devices operating up to 650 V have recently become commercially available. Further goal is to reach higher breakdown voltage which can be done via device engineering and material growth optimization.

    AlxGa1−xN is an ultrawide-bandgap (UWBG) semiconductor which is considered as a natural choice for next generation in the development of GaN-based HP electronic devices. This material attracts particular interest due to the possibility for bandgap tuning from 3.4 eV to 6 eV which allows nonlinear increase of avalanche breakdown field. Furthermore, both n- and p-type conductivity can be achieved on this material permitting variety of device design with reduced energy losses during operation. β−Ga2O3 is also a promising material for HP electronics because of its ultra-wide bandgap (4.8 eV) and a huge value of Baliga’s figure of merit (FOM) exceeding by far that of GaN. More interesting feature making this material attractive is the availability of low-cost natural substrates, and then the possibility to obtain high crystal quality of device structures.

    For the HP electronic devices thermal conductivity is one of the key parameters determining the device’s performance. The initial studies have shown that the thermal conductivity of AlxGa1−xN and β−Ga2O3 is quite low comparing with that of GaN. This is one of the biggest challenges slowing the development of these materials for HP device applications. Nevertheless, AlxGa1−xN- and β−Ga2O3-based field-effect transistors and Schottky-barrier diodes have been demonstrated showing performances superior to that of GaN. To optimize and maintain good performance and reliability, heat generated in the device active regions has to be effectively dissipated. Therefore the thermal conductivity of the materials in the device structures needs to be systematically studied and accurately determined. This information is critically important for the thermal management of the devices.

    Transient thermoreflectance (TTR) is a contactless nondestructive method for measuring of the thermal conductivity of materials. TTR, which is based on a pump-probe technique, has shown its potential in evaluation of the thermal conductivity in bulk crystals as well as in thin layers in hetero-epitaxial structures. The method requires an analysis of experimental data based on the fit of thermoreflectance transients with the solution of the one-dimensional heat transport equations by a least-square minimization of the fitting parameters. Such a procedure allows to extract not only the thermal conductivity of the constituent materials in the structures, but also the thermal boundary resistance at different hetero-interfaces.

    The main research results of the graduate studies presented in this licentiate thesis are summarized in three scientific papers.

    Paper I. In this paper thermal conductivity of β−Ga2O3 and high Al-content AlxGa1−xN thin layers was studied. For β−Ga2O3 the the effects of Sn doping and phonon-bondary scattering on the reduction of thermal conductivity were discussed. For the AlxGa1−xN we studied the effect of Al-Ga alloying which gives rise to phonon-alloy scattering. It was found that this scattering process accounts for low thermal conductivity of this material. Finally, a comparison for the thermal conductivity of the two materials was made.

    Paper II. In this paper the effect of layer thickness on the thermal conductivity of AlxGa1−xN layers grown by HVPE were investigated. Due to Al alloying the thermal conductivity of this material is degraded and reduced by more than one order of magnitude. On top of that we also observed further reduction of thermal conductivity when the layer thickness goes thinner. The mechanism of this phenomenon has been revealed by studying the phonon transport properties in bulk crystal and thin layer.

    Paper III. This study emphasizes the role of defects in GaN and AlxGa1−xN to the thermal conductivity of these materials. The dislocations, impurities, free carries, and random alloying have been separately studied and discussed. Thermal conductivity of samples containing these defects with various concentrations was measured and the results were interpreted by a theoretical model based on relaxation time approximation (RTA).

    List of papers
    1. Thermal conductivity of ultra-wide bandgap thin layers - High Al-content AlGaN and beta-Ga2O3
    Open this publication in new window or tab >>Thermal conductivity of ultra-wide bandgap thin layers - High Al-content AlGaN and beta-Ga2O3
    Show others...
    2020 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 579, article id 411810Article in journal (Refereed) Published
    Abstract [en]

    Transient thermoreflectance (TTR) technique is employed to study the thermal conductivity of beta-Ga2O3 and high Al-content AlxGa1-xN semiconductors, which are very promising materials for high-power device applications. The experimental data are analyzed with the Callaways model taking into account all relevant phonon scattering processes. Our results show that out-of-plane thermal conductivity of high Al-content AlxGa1-xN and (-201) beta-Ga2O3 is of the same order of magnitude and approximately one order lower than that of GaN or AlN. The low thermal conductivity is attributed to the dominant phonon-alloy scattering in AlxGa1-xN and to the strong Umklapp phonon-phonon scattering in beta-Ga2O3. It is also found that the phonon-boundary scattering is essential in thin beta-Ga2O3 and AlxGa1-xN layers even at high temperatures and the thermal conductivity strongly deviates from the common 1/T temperature dependence.

    Place, publisher, year, edition, pages
    ELSEVIER, 2020
    Keywords
    Thermal conductivity; Ga2O3; AlGaN
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-163652 (URN)10.1016/j.physb.2019.411810 (DOI)000510638200032 ()
    Conference
    8th South African Conference on Photonic Materials (SACPM)
    Note

    Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program [2016-05190]; Swedish Research Council VRSwedish Research Council [2016-00889, 2017-03714]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [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]; NSFNational Science Foundation (NSF) [CBET-1336464, DMR-1506159]

    Available from: 2020-02-18 Created: 2020-02-18 Last updated: 2023-12-28
    2. Correction: Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness (vol 117, 252102, 2020)
    Open this publication in new window or tab >>Correction: Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness (vol 117, 252102, 2020)
    Show others...
    2021 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 118, no 10, article id 109902Article in journal (Other academic) Published
    Abstract [en]

    n/a

    Place, publisher, year, edition, pages
    AMER INST PHYSICS, 2021
    Identifiers
    urn:nbn:se:liu:diva-174646 (URN)10.1063/5.0045312 (DOI)000629690200001 ()
    Available from: 2021-04-01 Created: 2021-04-01 Last updated: 2023-12-28Bibliographically approved
    Download full text (pdf)
    fulltext
    Download (png)
    presentationsbild
  • 8. Order onlineBuy this publication >>
    Tran, Dat
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Thermal conductivity of wide and ultra-wide bandgap semiconductors2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This PhD thesis presents experimental and theoretical studies of the thermal conductivity of wide and ultra-wide bandgap semiconductors including GaN, AlN, β-Ga2O3 binary compounds, and AlxGa1−xN, ScxAl1−xN, YxAl1−xN ternary alloys. Thermal conductivity measurements are conducted using the transient thermoreflectance (TTR) technique and the results are interpreted using analytical models based on the solution of the Boltzmann transport equation (BTE) within the relaxation time approximation (RTA). 

    The study is motivated by the increasing research interest in these material systems due to their potential for the development of high-power (HP) and high-frequency (HF) electronic devices. Due to its wide bandgap, high electrical field, and high electronic saturation velocity, GaN is an excellent material for fast-switching HP electronic devices. AlxGa1−xN is considered a natural choice for next-generation HP electronic devices since by tuning the bandgap from 3.4 eV to 6 eV a significant increase of the critical electric field and thus the device breakdown voltage, can be achieved. Furthermore, both n- and p-type conductivity can be realized in AlGaN allowing flexible device design. β-Ga2O3 is also promising for HP electronics because of its ultra-wide bandgap (4.8 eV) and a very high Baliga’s figure of merit (FOM) exceeding by far that of GaN. Moreover, the mature growth techniques of bulk β-Ga2O3 can enable low-cost substrates with high crystal quality. ScxAl1−xN and YxAl1−xN have recently emerged as a new class of III-nitride semiconductors. Due to the large piezoelectric coefficients and spontaneous polarization in these alloys, a very large density of two-dimensional electron gas (2DEG) can be achieved at (Sc,Y)xAl1−xN/GaN heterostructures enabling high mobility transistors (HEMTs) with an enhanced HF performance as compared with the common AlxGa1−xN/GaN HEMTs. 

    For any HP and HF device, the thermal conductivity of the constituent materials in the device structures is of crucial importance. Such devices operate at high currents, high voltages, and/or high frequencies, so a high Joule heat is generated in the device’s active region. This heat must be effectively dissipated in order to ensure high device performance and reliability. Therefore, understanding the materials’ thermal conductivity is essential for the device’s thermal management. 

    We have investigated different bulk materials and epitaxial layers and have established the effects of dislocation density, doping, alloying, layer thickness, and crystal orientation on thermal conductivity. The results presented in this Ph.D. thesis give new insights into the thermal properties of wide and ultra-wide semiconductors and could be useful for the design, optimization, and thermal management of electronic devices based on these materials. 

    The main research results presented in this Ph.D. thesis are summarized in six scientific papers. 

    Paper I is focused on studying the thermal conductivity of high Al-content AlxGa1−xN and β-Ga2O3 thin layers. For β-Ga2O3 layers the effect of Sn doping on their thermal conductivity is also studied. The experimental measurements are performed in a temperature range of 280-350 K. A modified Callaway’s model is employed for the interpretation of the results. Calculations of the thickness-dependent thermal conductivity reveal quite different transport mechanisms of the two materials. 

    Paper II presents experimental results of the thermal conductivity of thick AlxGa1−xN layers. A detailed discussion of the phonon-alloy scattering which is the main mechanism limiting the thermal conductivity of AlxGa1−xN is presented. Analyzing the interplay between the phonon-alloy scattering and the phonon-boundary scattering the experimentally observed thickness dependence of the thermal conductivity is explained. 

    Paper III is devoted to studying the role of defects on the thermal conductivity of AlxGa1−xN alloys with 0 ≤ x ≤ 1. The effect of dislocations, impurities, free carriers, and alloying have been separately studied and discussed. The thermal conductivity of samples with various concentrations of the defect is measured and the results are interpreted using a theoretical model based on the solution of the BTE equation within the RTA. 

    Paper IV focuses on the thermal conductivity study of ScxAl1−xN and YxAl1−xN alloys. The experimental measurements are performed for layers having compositions in the range of 0 ≤ x ≤ 0.22. The effect of phonon-alloy scattering in these alloy materials is discussed and compared with other phonon scattering processes. The experimental results are interpreted within the frame of a modified Callaway’s model in combination with ab-initio calculation for phonon dispersions and mode Grüneisen parameters. 

    Paper V investigates the thermal conductivity anisotropy of bulk GaN. The thermal conductivity along the c- and m-axis crystallographic directions of wurtzite GaN is measured in a temperature range of 80-400 K. Experimental observations are elaborated by an analysis of the anisotropy of the phonon group velocity, the Debye temperature and the mode Grüneisen parameters. 

    Paper VI explores the effects of doping and free carriers on the thermal conductivity of bulk GaN and homoepitaxial layers and heteroepitaxial GaN layers via both experimental and theoretical approaches. The impurities considered include Si, O, Mg, and Fe. The experimental results are analyzed using a non-Debye RTA model in combination with ab-initio calculations of the phonon dispersion. 

    List of papers
    1. Thermal conductivity of ultra-wide bandgap thin layers - High Al-content AlGaN and beta-Ga2O3
    Open this publication in new window or tab >>Thermal conductivity of ultra-wide bandgap thin layers - High Al-content AlGaN and beta-Ga2O3
    Show others...
    2020 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 579, article id 411810Article in journal (Refereed) Published
    Abstract [en]

    Transient thermoreflectance (TTR) technique is employed to study the thermal conductivity of beta-Ga2O3 and high Al-content AlxGa1-xN semiconductors, which are very promising materials for high-power device applications. The experimental data are analyzed with the Callaways model taking into account all relevant phonon scattering processes. Our results show that out-of-plane thermal conductivity of high Al-content AlxGa1-xN and (-201) beta-Ga2O3 is of the same order of magnitude and approximately one order lower than that of GaN or AlN. The low thermal conductivity is attributed to the dominant phonon-alloy scattering in AlxGa1-xN and to the strong Umklapp phonon-phonon scattering in beta-Ga2O3. It is also found that the phonon-boundary scattering is essential in thin beta-Ga2O3 and AlxGa1-xN layers even at high temperatures and the thermal conductivity strongly deviates from the common 1/T temperature dependence.

    Place, publisher, year, edition, pages
    ELSEVIER, 2020
    Keywords
    Thermal conductivity; Ga2O3; AlGaN
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-163652 (URN)10.1016/j.physb.2019.411810 (DOI)000510638200032 ()
    Conference
    8th South African Conference on Photonic Materials (SACPM)
    Note

    Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program [2016-05190]; Swedish Research Council VRSwedish Research Council [2016-00889, 2017-03714]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [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]; NSFNational Science Foundation (NSF) [CBET-1336464, DMR-1506159]

    Available from: 2020-02-18 Created: 2020-02-18 Last updated: 2023-12-28
    2. Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness
    Open this publication in new window or tab >>Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness
    Show others...
    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
    3. Thermal conductivity of AlxGa1-xN (0 <= x <= 1) epitaxial layers
    Open this publication in new window or tab >>Thermal conductivity of AlxGa1-xN (0 <= x <= 1) epitaxial layers
    Show others...
    2022 (English)In: Physical Review Materials, E-ISSN 2475-9953, Vol. 6, no 10, article id 104602Article in journal (Refereed) Published
    Abstract [en]

    AlxGa1-xN ternary alloys are emerging ultrawide band gap semiconductor materials for high-power electronics applications. The heat dissipation, which mainly depends on the thermal conductivity of the constituent material in the device structures, is the key for device performance and reliability. However, the reports on the thermal conductivity of AlxGa1-xN alloys are very limited. Here, we present a comprehensive study of the thermal conductivity of AlxGa1-xN in the entire Al composition range. Thick AlxGa1-xN layers grown by metal-organic chemical vapor deposition on GaN/sapphire and GaN/SiC templates are examined. The thermal conductivity measurements are done by the transient thermoreflectance method at room temperature. The effects of the Al composition, dislocation density, Si doping, and layer thickness on the thermal conductivity of AlxGa1-xN layers are thoroughly investigated. All experimental data are fitted by the modified Callaway model within the virtual crystal approximation, and the interplay between the different phonon scattering mechanisms is analyzed and discussed.

    Place, publisher, year, edition, pages
    American Physical Society, 2022
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-189952 (URN)10.1103/PhysRevMaterials.6.104602 (DOI)000876930700002 ()
    Note

    Funding Agencies|Swedish Governmental Agency for Innovation Systems (VINNOVA) [2016-05190]; Swedish Research Council [2016-00889, 2017-03714]; 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 [CBET-1336464, DMR-1506159]

    Available from: 2022-11-15 Created: 2022-11-15 Last updated: 2023-12-28
    4. Thermal conductivity of ScxAl1-xN and YxAl1-xN alloys
    Open this publication in new window or tab >>Thermal conductivity of ScxAl1-xN and YxAl1-xN alloys
    Show others...
    2023 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 122, no 18, article id 182107Article in journal (Refereed) Published
    Abstract [en]

    Owing to their very large piezoelectric coefficients and spontaneous polarizations, (Sc,Y) xAl(1-x)N alloys have emerged as a new class of III-nitride semiconductor materials with great potential for high-frequency electronic and acoustic devices. The thermal conductivity of constituent materials is a key parameter for design, optimization, and thermal management of such devices. In this study, transient thermoreflectance technique is applied to measure the thermal conductivity of ScxAl1-xN and YxAl1-xN (0 = x = 0.22) layers grown by magnetron sputter epitaxy in the temperature range of 100-400 K. The room-temperature thermal conductivity of both alloys is found to decrease significantly with increasing Sc(Y) composition compared to that of AlN. We also found that the thermal conductivity of YxAl1-xN is lower than that of ScxAl1-xN for all studied compositions. In both alloys, the thermal conductivity increases with the temperature up to 250 K and then saturates. The experimental data are analyzed using a model based on the solution of the phonon Boltzmann transport equation within the relaxation time approximation. The contributions of different phonon-scattering mechanisms to the lattice thermal conductivity of (Sc,Y) xAl(1-x)N alloys are identified and discussed.

    Place, publisher, year, edition, pages
    AIP Publishing, 2023
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-195334 (URN)10.1063/5.0145847 (DOI)000982006100006 ()
    Note

    Funding Agencies|Swedish Governmental Agency for innovation systems (VINOVA) under the Competence Center Program [2022-03139]; Swedish Research Council VR [2022-04812]; Swedish Foundation for Strategic Research [EM16-0024]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University, Faculty Grant SFO Mat LiU [CBET-1336464, DMR-1506159]

    Available from: 2023-06-21 Created: 2023-06-21 Last updated: 2024-05-04
    Download full text (pdf)
    fulltext
    Download (png)
    presentationsbild
  • 9.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Blumenschein, Nicholas
    North Carolina State Univ, NC 27695 USA.
    Mock, Alyssa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Naval Res Lab, DC 20375 USA.
    Sukkaew, Pitsiri
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Zhang, Hengfang
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Muth, John F.
    North Carolina State Univ, NC 27695 USA.
    Paskova, Tania
    North Carolina State Univ, NC 27695 USA.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. North Carolina State Univ, NC 27695 USA.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Thermal conductivity of ultra-wide bandgap thin layers - High Al-content AlGaN and beta-Ga2O32020In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 579, article id 411810Article in journal (Refereed)
    Abstract [en]

    Transient thermoreflectance (TTR) technique is employed to study the thermal conductivity of beta-Ga2O3 and high Al-content AlxGa1-xN semiconductors, which are very promising materials for high-power device applications. The experimental data are analyzed with the Callaways model taking into account all relevant phonon scattering processes. Our results show that out-of-plane thermal conductivity of high Al-content AlxGa1-xN and (-201) beta-Ga2O3 is of the same order of magnitude and approximately one order lower than that of GaN or AlN. The low thermal conductivity is attributed to the dominant phonon-alloy scattering in AlxGa1-xN and to the strong Umklapp phonon-phonon scattering in beta-Ga2O3. It is also found that the phonon-boundary scattering is essential in thin beta-Ga2O3 and AlxGa1-xN layers even at high temperatures and the thermal conductivity strongly deviates from the common 1/T temperature dependence.

    Download full text (pdf)
    fulltext
  • 10.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Delgado Carrascon, Rosalia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Iwaya, Motoaki
    Meijo Univ, Japan.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Thermal conductivity of AlxGa1-xN (0 <= x <= 1) epitaxial layers2022In: Physical Review Materials, E-ISSN 2475-9953, Vol. 6, no 10, article id 104602Article in journal (Refereed)
    Abstract [en]

    AlxGa1-xN ternary alloys are emerging ultrawide band gap semiconductor materials for high-power electronics applications. The heat dissipation, which mainly depends on the thermal conductivity of the constituent material in the device structures, is the key for device performance and reliability. However, the reports on the thermal conductivity of AlxGa1-xN alloys are very limited. Here, we present a comprehensive study of the thermal conductivity of AlxGa1-xN in the entire Al composition range. Thick AlxGa1-xN layers grown by metal-organic chemical vapor deposition on GaN/sapphire and GaN/SiC templates are examined. The thermal conductivity measurements are done by the transient thermoreflectance method at room temperature. The effects of the Al composition, dislocation density, Si doping, and layer thickness on the thermal conductivity of AlxGa1-xN layers are thoroughly investigated. All experimental data are fitted by the modified Callaway model within the virtual crystal approximation, and the interplay between the different phonon scattering mechanisms is analyzed and discussed.

    Download full text (pdf)
    fulltext
  • 11.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Delgado Carrascon, Rosalia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Muth, John F.
    NCSU, NC 27695 USA.
    Paskova, Tania
    NCSU, NC 27695 USA.
    Nawaz, Muhammad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Hitachi ABB Power Grids, Sweden.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. NCSU, NC 27695 USA.
    Correction: Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness (vol 117, 252102, 2020)2021In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 118, no 10, article id 109902Article in journal (Other academic)
    Abstract [en]

    n/a

  • 12.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Delgado Carrascon, Rosalia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Muth, John F.
    NCSU, NC 27695 USA.
    Paskova, Tania
    NCSU, NC 27695 USA.
    Nawaz, Muhammad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Hitachi ABB Power Grids, Sweden.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Paskov, Plamen P.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. NCSU, NC 27695 USA.
    Correction: Erratum: “Phonon-boundary scattering and thermal transport in AlxGa1−xN: Effect of layer thickness” [Appl. Phys. Lett. 117, 252102 (2020)]2021In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 118, no 18, article id 189901Article in journal (Other academic)
  • 13.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Delgado Carrascon, Rosalia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Muth, John F.
    Department of Electrical and Computer Engineering, NCSU, Raleigh, North Carolina, USA.
    Paskova, Tania
    Department of Electrical and Computer Engineering, NCSU, Raleigh, North Carolina, USA.
    Nawaz, Muhammad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Hitachi ABB Power Grids, Sweden.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Paskov, Plamen P.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Department of Electrical and Computer Engineering, NCSU, Raleigh, North Carolina, USA.
    Phonon-boundary scattering and thermal transport in AlxGa1-xN: Effect of layer thickness2020In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 117, no 25, article id 252102Article in journal (Refereed)
    Abstract [en]

    Thermal conductivity of AlxGa1-xN layers with 0 &lt;= x &lt;= 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.

    Download full text (pdf)
    fulltext
  • 14.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Japan Adv Inst Sci & Technol JAIST, Japan.
    Islam, Md Earul
    Japan Adv Inst Sci & Technol JAIST, Japan.
    Higashimine, Koichi
    Japan Adv Inst Sci & Technol JAIST, Japan.
    Akabori, Masashi
    Japan Adv Inst Sci & Technol JAIST, Japan.
    Self-catalyst growth and characterization of wurtzite GaAs/InAs core/ shell nanowires2021In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 564, article id 126126Article in journal (Refereed)
    Abstract [en]

    Research on nanowire (NW) growth of III-V semiconductors including GaAs and InAs demonstrated the ability to grow in both wurtzite (WZ) and zincblende (ZB) polymorphs. However, the control of crystal phase in selfcatalyzed NW growth is still a remaining challenge. In this study we report a controlled growth of GaAs/InAs core/shell nanowires in WZ phase using self-catalyzed molecular beam epitaxy (MBE). The GaAs NWs having pure WZ crystal were achieved and attributed to the effect of small wetting angle, which is realized by supplying high V/III ratio. Furthermore, the WZ formation is shown to be uninfluenced by NW diameter. For the wetting angle larger than 90?, mixed phase starts to be observed. The InAs shell is planarly grown on six m-plane facets of the GaAs core NWs leading to the same strain states along a and c axes of growth plane, in which tensile and compressive strains are observed for GaAs core and InAs shell, respectively. High-resolution transmission electron microscopy (HR-TEM) reveals a few misfit dislocations (-0.03 nm- 1) at GaAs/InAs interface indicating insignificant strain relief via creating misfit dislocation. Electrical characterization of the hetero-wires shows that the InAs shell exhibits n-type conduction. A room-temperature sheet carrier concentration at zero gate-bias of 2.5 ? 1012 cm-2 and the corresponding carrier mobility of - 900 cm2 V-1 s- 1 are demonstrated.

  • 15.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Paskova, Tania
    NCSU, NC USA.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    On the thermal conductivity anisotropy in wurtzite GaN2023In: AIP Advances, E-ISSN 2158-3226, Vol. 13, no 9, article id 095009Article in journal (Refereed)
    Abstract [en]

    GaN-based power devices operating at high currents and high voltages are critically affected by the dissipation of Joule heat generated in the active regions. Consequently, knowledge of GaN thermal conductivity is crucial for effective thermal management, needed to ensure optimal device performance and reliability. Here, we present a study on the thermal conductivity of bulk GaN in crystallographic directions parallel and perpendicular to the c-axis. Thermal conductivity measurements are performed using the transient thermoreflectance technique. The experimental results are compared with a theoretical calculation based on a solution of the Boltzmann transport equation within the relaxation time approximation and taking into account the exact phonon dispersion. All factors that determine the thermal conductivity anisotropy are analyzed, and the experimentally observed small anisotropy factor is explained.

    Download full text (pdf)
    fulltext
  • 16.
    Tran, Dat
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Zukauskaite, Agne
    Fraunhofer Inst Organ Elect Electron Beam & Plasma, Germany; Tech Univ Dresden, Germany.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Thermal conductivity of ScxAl1-xN and YxAl1-xN alloys2023In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 122, no 18, article id 182107Article in journal (Refereed)
    Abstract [en]

    Owing to their very large piezoelectric coefficients and spontaneous polarizations, (Sc,Y) xAl(1-x)N alloys have emerged as a new class of III-nitride semiconductor materials with great potential for high-frequency electronic and acoustic devices. The thermal conductivity of constituent materials is a key parameter for design, optimization, and thermal management of such devices. In this study, transient thermoreflectance technique is applied to measure the thermal conductivity of ScxAl1-xN and YxAl1-xN (0 = x = 0.22) layers grown by magnetron sputter epitaxy in the temperature range of 100-400 K. The room-temperature thermal conductivity of both alloys is found to decrease significantly with increasing Sc(Y) composition compared to that of AlN. We also found that the thermal conductivity of YxAl1-xN is lower than that of ScxAl1-xN for all studied compositions. In both alloys, the thermal conductivity increases with the temperature up to 250 K and then saturates. The experimental data are analyzed using a model based on the solution of the phonon Boltzmann transport equation within the relaxation time approximation. The contributions of different phonon-scattering mechanisms to the lattice thermal conductivity of (Sc,Y) xAl(1-x)N alloys are identified and discussed.

    Download full text (pdf)
    fulltext
  • 17.
    Zhang, Hengfang
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Persson, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Papamichail, Alexis
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Tran, Dat
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Paskov, Plamen P.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Polarity Control by Inversion Domain Suppression in N-Polar III-Nitride Heterostructures2023In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 23, no 2, p. 1049-1056Article in journal (Refereed)
    Abstract [en]

    Nitrogen-polar III-nitride heterostructures offer advantages over metal-polar structures in high frequency and high power applications. However, polarity control in III-nitrides is difficult to achieve as a result of unintentional polarity inversion domains (IDs). Herein, we present a comprehensive structural investigation with both atomic detail and thermodynamic analysis of the polarity evolution in low-and high-temperature AlN layers on on-axis and 4 degrees off-axis carbon-face 4H-SiC (000 (1) over bar) grown by hot-wall metal organic chemical vapor deposition. A polarity control strategy has been developed by variation of thermodynamic Al supersaturation and substrate misorientation angle in order to achieve the desired growth mode and polarity. We demonstrate that IDs are completely suppressed for high-temperature AlN nucleation layers when a step-flow growth mode is achieved on the off-axis substrates. We employ this approach to demonstrate high quality N-polar epitaxial AlGaN/GaN/AlN heterostructures.

    Download full text (pdf)
    fulltext
1 - 17 of 17
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf