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  • 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.
    Richter, Steffen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden; Lund Univ, Sweden.
    Nawaz, Muhammad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Hitachi Energy, Sweden.
    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.
    Hot-Wall MOCVD for High-Quality Homoepitaxy of GaN: Understanding Nucleation and Design of Growth Strategies2022In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 22, no 12, p. 7021-7030Article in journal (Refereed)
    Abstract [en]

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

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  • 3.
    Emminger, Carola
    et al.
    Department of Physics, New Mexico State University, Las Cruces, USA.
    Abadizaman, Farzin
    Department of Condensed Matter Physics, Masaryk University, Brno, Czech Republic.
    Samarasingha, Nuwanjula S.
    Department of Physics, New Mexico State University, Las Cruces, USA.
    Menendez, Jose
    Department of Physics, Arizona State University, Tempe, USA.
    Espinoza, Shirly
    ELI Beamlines, Fyzikální ústav AV ČR, Dolní Břežany, Czech Republic.
    Richter, Steffen
    ELI Beamlines, Fyzikální ústav AV ČR, Dolní Břežany, Czech Republic.
    Rebarz, Mateusz
    ELI Beamlines, Fyzikální ústav AV ČR, Dolní Břežany, Czech Republic.
    Herrfurth, Oliver
    Active Fiber Systems GmbH, Jena, Germany.
    Zahradnik, Martin
    ELI Beamlines, Fyzikální ústav AV ČR, Dolní Břežany, Czech Republic.
    Schmidt-Grund, Rudiger
    Institut für Physik Technische Universiät Ilmenau, Ilmenau, Germany.
    Andreasson, Jakob
    ELI Beamlines, Fyzikální ústav AV ČR, Dolní Břežany, Czech Republic.
    Zollner, Stefan
    Department of Physics, New Mexico State University, Las Cruces, USA.
    Analysis of temperature-dependent and time-resolved ellipsometry spectra of Ge2021Conference paper (Refereed)
    Abstract [en]

    The dielectric function of Ge measured with static and time-resolved spectroscopic ellipsometry is analyzed using linear filtering techniques to investigate the temperature dependence of the direct band gap, as well as the temporal evolvement of critical points obtained from femtosecond pump-probe ellipsometry measurements.

  • 4.
    Emminger, Carola
    et al.
    Department of Physics, New Mexico State University, Las Cruces, NM, USA; Department of Condensed Matter Physics, Masaryk University, Brno, Czech Republic; Felix-Bloch-Institut für Festkörperphysik, Universität Leipzig, Leipzig, Germany; Institut für Physik, Humboldt-Universität zu Berlin, Berlin, Germany.
    Espinoza, Shirly
    ELI Beamlines, Fyzikální ústav AV ČR v.v.i., Dolní Břežany, Czech Republic.
    Richter, Steffen
    ELI Beamlines, Fyzikální ústav AV ČR v.v.i., Za Radnicí 835, 25241 Dolní Břežany, Czech Republic; Department of Physics, Faculty of Engineering (LTH), Lund University, Lund, Sweden.
    Rebarz, Mateusz
    ELI Beamlines, Fyzikální ústav AV ČR v.v.i., Dolní Břežany, Czech Republic.
    Herrfurth, Oliver
    Felix-Bloch-Institut für Festkörperphysik, Universität Leipzig, Leipzig, Germany; Active Fiber Systems GmbH, Jena, Germany.
    Zahradník, Martin
    ELI Beamlines, Fyzikální ústav AV ČR v.v.i., Dolní Břežany, Czech Republic.
    Schmidt-Grund, Rüdiger
    Felix-Bloch-Institut für Festkörperphysik, Universität Leipzig, Leipzig, Germany; Institut für Physik, Technische Universität Ilmenau, Ilmenau, Germany.
    Andreasson, Jakob
    ELI Beamlines, Fyzikální ústav AV ČR v.v.i., Dolní Břežany, Czech Republic.
    Zollner, Stefan
    Department of Physics, New Mexico State University, Las Cruces, NM, USA.
    Coherent acoustic phonon oscillations and transient critical point parameters of Ge from femtosecond pump‐probe ellipsometry2022In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 16, no 7, article id 2200058Article in journal (Refereed)
    Abstract [en]

    Herein, the complex pseudodielectric function of Ge and Si from femtosecond pump–probe spectroscopic ellipsometry with 267, 400, and 800 nm pump–pulse wavelengths is analyzed by fitting analytical lineshapes to the second derivatives of the pseudodielectric function with respect to energy. This yields the critical point parameters (threshold energy, lifetime broadening, amplitude, and excitonic phase angle) of E 1 and E 1 + Δ 1 in Ge and E 1 in Si as functions of delay time. Coherent longitudinal acoustic phonon oscillations with a period of about 11 ps are observed in the transient critical point parameters of Ge. From the amplitude of these oscillations, the laser-induced strain is found to be on the order of 0.03% for Ge measured with the 800 nm pump pulse, which is in reasonable agreement with the strain calculated from theory. 

  • 5.
    Espinoza, Shirly
    et al.
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Samparisi, Fabio
    Institute of Photonics and Nanotechnologies, National Council for Research, Via Trasea 7, 35131 Padova, Italy.
    Frassetto, Fabio
    Institute of Photonics and Nanotechnologies, National Council for Research, Via Trasea 7, 35131 Padova, Italy.
    Richter, Steffen
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Rebarz, Mateusz
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Finke, Ondrej
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic; Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Brehova 7, 115 19 Prague, Czech Republic.
    Albrecht, Martin
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic; Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Brehova 7, 115 19 Prague, Czech Republic.
    Jurkovic, Matej
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic; Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Brehova 7, 115 19 Prague, Czech Republic.
    Hort, Ondrej
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Fabris, Nicola
    Institute of Photonics and Nanotechnologies, National Council for Research, Via Trasea 7, 35131 Padova, Italy.
    Zymaková, Anna
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Mai, Dong Du
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Antipenkov, Roman
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Nejdl, Jaroslav
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Poletto, Luca
    Institute of Photonics and Nanotechnologies, National Council for Research, Via Trasea 7, 35131 Padova, Italy.
    Andreasson, Jakob
    Institute of Physics, Czech Academy of Science, Na Slovance 2, 18221 Prague, Czech Republic.
    Characterization of the high harmonics source for the VUV ellipsometer at ELI Beamlines2020In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754, Journal of Vacuum Science & Technology B, Vol. 38, no 2Article in journal (Refereed)
    Abstract [en]

    In this paper, the authors present the characterization experiments of a 20 fs vacuum ultraviolet beam from a high harmonic generation source. The beam hits a silicon sample and passes a triple reflection gold polarizer located inside an ultrahigh vacuum chamber. The polarizer’s Malus curve was obtained; the total acquisition time for each point of the curve was 30 s. This aims to be the first vacuum ultraviolet time-resolved user station dedicated to ellipsometry. The high harmonic beam is generated by a 12 mJ, 1 kHz, 20 fs, in-house-developed laser and detected by a back-illuminated charge-coupled device. 

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  • 6.
    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.

  • 7.
    Herrfurth, O.
    et al.
    Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Linnéstraße 5, 04103 Leipzig, Germany.
    Richter, Steffen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. ELI Beamlines/Fyzikální ústav AV CR, v.v.i., Za Radnicí 835, Dolní Bˇ ˇ režany, Czech Republic.
    Rebarz, M.
    ELI Beamlines/Fyzikální ústav AV CR, v.v.i., Za Radnicí 835, Dolní Bˇ ˇ režany, Czech Republic.
    Espinoza, S.
    ELI Beamlines/Fyzikální ústav AV CR, v.v.i., Za Radnicí 835, Dolní Bˇ ˇ režany, Czech Republic.
    Zúñiga-Pérez, J.
    Université Côte d’Azur, CRHEA-CNRS, rue Bernard Grégory, Valbonne, France.
    Deparis, C.
    Université Côte d’Azur, CRHEA-CNRS, rue Bernard Grégory, Valbonne, France.
    Leveillee, J.
    The University of Texas at Austin, Oden Institute for Computational Engineering and Sciences, 201 E. 24th Street, P.O. Box 4.102, Austin, Texas IL 78712-1229, USA.
    Schleife, A.
    University of Illinois at Urbana-Champaign, Dep. of Materials Science and Engineering, 1304 W. Green St., Urbana, IL 61801, USA.
    Grundmann, M.
    Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Linnéstraße 5, 04103 Leipzig, Germany.
    Andreasson, J.
    ELI Beamlines/Fyzikální ústav AV CR, v.v.i., Za Radnicí 835, Dolní Bˇ ˇ režany, Czech Republic.
    Schmidt-Grund, R.
    Institut für Physik, Technische Universität Ilmenau, Weimarer Straße 25, 98693 Ilmenau, Germany.
    Transient birefringence and dichroism in ZnO studied with fs-time-resolved spectroscopic ellipsometry2021In: Physical Review Research, E-ISSN 2643-1564, Vol. 3, no 1Article in journal (Refereed)
    Abstract [en]

    The full transient dielectric-function (DF) tensor of ZnO after UV-laser excitation in the spectral range 1.4–3.6 eV is obtained by measuring an m-plane-oriented ZnO thin film with femtosecond (fs)-time-resolved spectroscopic ellipsometry. From the merits of the method, we can distinguish between changes in the real and the imaginary part of the DF as well as changes in birefringence and dichroism, respectively. We find pump-induced switching from positive to negative birefringence in almost the entire measured spectral range for about 1 ps. Simultaneously, weak dichroism in the spectral range below 3.0 eV hints at contributions of inter-valence-band transitions. Line-shape analysis of the DF above the band gap based on discrete exciton, exciton-continuum, and exciton-phonon-complex contributions shows a maximal dynamic increase in the transient exciton energy by 80 meV. The absorption coefficient below the band gap reveals an exponential line shape attributed to Urbach-rule absorption mediated by exciton–longitudinal-optic-phonon interaction. The transient DF is supported by first-principles calculations for 1020cm−3 excited electron-hole pairs in ideal bulk ZnO.

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  • 8.
    Knight, Sean Robert
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Solid State Physics and NanoLund, Lund University, Lund, 22100, Sweden.
    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, Lund, 22100, Sweden.
    Papamichail, Alexis
    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.
    Armakavicius, Nerijus
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Guo, Shiqi
    Linköping University, Department of Physics, Chemistry and Biology. 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.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Rindert, Viktor
    Solid State Physics and NanoLund, Lund University, Lund, 22100, Sweden.
    Persson, Per O. Å.
    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.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Solid State Physics and NanoLund, Lund University, Lund, 22100, Sweden; Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, 68588, NE, United States.
    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, Lund, 22100, Sweden.
    Room temperature two-dimensional electron gas scattering time, effective mass, and mobility parameters in AlxGa1−xN/GaN heterostructures (0.07 ≤ x ≤ 0.42)2023In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 134, no 18, article id 185701Article in journal (Refereed)
    Abstract [en]

    Al xGa 1−xN/GaN high-electron-mobility transistor (HEMT) structures are key components in electronic devices operating at gigahertz or higher frequencies. In order to optimize such HEMT structures, understanding their electronic response at high frequencies and room temperature is required. Here, we present a study of the room temperature free charge carrier properties of the two-dimensional electron gas (2DEG) in HEMT structures with varying Al content in the Al xGa 1−xN barrier layers between x=0.07 and x=0.42⁠. We discuss and compare 2DEG sheet density, mobility, effective mass, sheet resistance, and scattering times, which are determined by theoretical calculations, contactless Hall effect, capacitance-voltage, Eddy current, and cavity-enhanced terahertz optical Hall effect (THz-OHE) measurements using a low-field permanent magnet (0.6 T). From our THz-OHE results, we observe that the measured mobility reduction from x=0.13 to x=0.42 is driven by the decrease in 2DEG scattering time, and not the change in effective mass. For x<0.42⁠, the 2DEG effective mass is found to be larger than for electrons in bulk GaN, which in turn, contributes to a decrease in the principally achievable mobility. From our theoretical calculations, we find that values close to 0.3 m0 can be explained by the combined effects of conduction band nonparabolicity, polarons, and hybridization of the electron wavefunction through penetration into the barrier layer.

  • 9.
    Knight, Sean Robert
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden; Lund Univ, Sweden.
    Richter, Steffen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden; 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, NE 68588 USA.
    Korlacki, Rafal
    Univ Nebraska, NE 68588 USA.
    Stanishev, Vallery
    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.
    Schubert, Mathias
    Lund Univ, Sweden; Lund Univ, Sweden.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden; Lund Univ, Sweden.
    Terahertz permittivity parameters of monoclinic single crystal lutetium oxyorthosilicate2024In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 124, no 3, article id 032101Article in journal (Refereed)
    Abstract [en]

    The anisotropic permittivity parameters of monoclinic single crystal lutetium oxyorthosilicate, Lu2SiO5 (LSO), have been determined in the terahertz spectral range. Using terahertz generalized spectroscopic ellipsometry (THz-GSE), we obtained the THz permittivities along the a, b, and c? crystal directions, which correspond to the ea; eb, and ec? on-diagonal tensor elements. The associated off diagonal tensor element eac? was also determined experimentally, which is required to describe LSO's optical response in the monoclinic a-c crystallographic plane. From the four tensor elements obtained in the model fit, we calculate the direction of the principal dielectric axes in the a-c plane. We find good agreementwhen comparing THz-GSE permittivities to the static permittivity tensors from previous infrared and density functional theory studies.

  • 10.
    Papamichail, Alexis
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Persson, Axel
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. 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.
    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.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Del Castillo, R. Ferrand-Drake
    Chalmers Univ Technol, Sweden.
    Thorsell, M.
    Chalmers Univ Technol, Sweden; Saab AB, Sweden.
    Hjelmgren, H.
    Chalmers Univ Technol, Sweden.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Rorsman, N.
    Chalmers Univ Technol, Sweden.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Tuning composition in graded AlGaN channel HEMTs toward improved linearity for low-noise radio-frequency amplifiers2023In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 122, no 15, article id 153501Article in journal (Refereed)
    Abstract [en]

    Compositionally graded channel AlGaN/GaN high electron mobility transistors (HEMTs) offer a promising route to improve device linearity, which is necessary for low-noise radio-frequency amplifiers. In this work, we demonstrate different grading profiles of a 10-nm-thick AlxGa1-xN channel from x = 0 to x = 0.1 using hot-wall metal-organic chemical vapor deposition (MOCVD). The growth process is developed by optimizing the channel grading and the channel-to-barrier transition. For this purpose, the Al-profiles and the interface sharpness, as determined from scanning transmission electron microscopy combined with energy-dispersive x-ray spectroscopy, are correlated with specific MOCVD process parameters. The results are linked to the channel properties (electron density, electron mobility, and sheet resistance) obtained by contactless Hall and terahertz optical Hall effect measurements coupled with simulations from solving self-consistently Poisson and Schrodinger equations. The impact of incorporating a thin AlN interlayer between the graded channel and the barrier layer on the HEMT properties is investigated and discussed. The optimized graded channel HEMT structure is found to have similarly high electron density (similar to 9 x 10(12) cm(-2)) as the non-graded conventional structure, though the mobility drops from similar to 2360 cm(2)/V s in the conventional to similar to 960 cm(2)/V s in the graded structure. The transconductance g(m) of the linearly graded channel HEMTs is shown to be flatter with smaller g(m) and g(m) as compared to the conventional non-graded channel HEMT implying improved device linearity. (c) 2023 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/).

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  • 11.
    Richter, Steffen
    et al.
    ELI Beamlines/Fyzikální ústav AV CR, v.v.i., Za Radnicí 835, ˇ 25241 Dolní Bˇrežany, Czech Republic.
    Espinoza, S.
    ELI Beamlines/Fyzikální ústav AV CR, v.v.i., Za Radnicí 835, ˇ 25241 Dolní Bˇrežany, Czech Republic.
    Andreasson, J.
    Chalmers tekniska högskola, Institutionen för fysik, Kemigården 1, 41296 Göteborg, Sweden.
    Spectral and Polarization Properties of VUV-Mirrors for Experiments at a HHG Beamline2020In: X-Ray Lasers 2018, Springer International Publishing , 2020, p. 175-179Conference paper (Refereed)
    Abstract [en]

    For polarization-resolved reflection experiments such as ellipsometry, not only is high reflectivity in a wide spectral range required for mirrors but also the quality of their polarization response is important. Furthermore, for VUV ellipsometry, optimal angles of incidence at the sample are between $$45^\circ $$ and $$60^\circ $$ with respect to the surface normal. In the best case, a setup should even allow variable angles. This requires reflective optics working at non-grazing incidence. In this theoretical study, a selection of potentially relevant materials and mirror designs for broadband use in the VUV is investigated. Based on the available tabulated databases of optical constants, we performed transfer-matrix calculations to obtain reflectance as well as polarization-response spectra in the desired VUV range up to 50 eV. From the variety of materials, we discuss metals that are otherwise commonly used at grazing incidence, Si, SiC, and as representatives for coating layers MgF$$_2$$, SiO$$_2$$, and Al$$_2$$O$$_3$$. While SiC is most universal, Si with only native oxide layer performs well especially below 25 eV. Aluminum has good properties but oxide layers are very detrimental, as protective coatings are in general.

  • 12.
    Richter, Steffen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. ELI Beamlines Fyzikalni Ustav AV CR, Czech Republic; Univ Leipzig, Germany.
    Herrfurth, Oliver
    Univ Leipzig, Germany.
    Espinoza, Shirly
    ELI Beamlines Fyzikalni Ustav AV CR, Czech Republic.
    Rebarz, Mateusz
    ELI Beamlines Fyzikalni Ustav AV CR, Czech Republic.
    Kloz, Miroslav
    ELI Beamlines Fyzikalni Ustav AV CR, Czech Republic.
    Leveillee, Joshua A.
    Univ Illinois, IL 61801 USA.
    Schleife, Andre
    Univ Illinois, IL 61801 USA.
    Zollner, Stefan
    New Mexico State Univ, NM 88003 USA; Fyzikalni Ustav AV CR, Czech Republic.
    Grundmann, Marius
    Univ Leipzig, Germany.
    Andreasson, Jakob
    ELI Beamlines Fyzikalni Ustav AV CR, Czech Republic.
    Schmidt-Grund, Ruediger
    Univ Leipzig, Germany; Tech Univ Ilmenau, Germany.
    Ultrafast dynamics of hot charge carriers in an oxide semiconductor probed by femtosecond spectroscopic ellipsometry2020In: New Journal of Physics, E-ISSN 1367-2630, Vol. 22, no 8, article id 083066Article in journal (Refereed)
    Abstract [en]

    Many linked processes occur concurrently in strongly excited semiconductors, such as interband and intraband absorption, scattering of electrons and holes by the heated lattice, Pauli blocking, bandgap renormalization and the formation of Mahan excitons. In this work, we disentangle their dynamics and contributions to the optical response of a ZnO thin film. Using broadband pump-probe ellipsometry, we can directly and unambiguously obtain the real and imaginary part of the transient dielectric function which we compare with first-principles simulations. We find interband and excitonic absorption partially blocked and screened by the photo-excited electron occupation of the conduction band and hole occupation of the valence band (absorption bleaching). Exciton absorption turns spectrally narrower upon pumping and sustains the Mott transition, indicating Mahan excitons. Simultaneously, intra-valence-band transitions occur at sub-picosecond time scales after holes scatter to the edge of the Brillouin zone. Our results pave new ways for the understanding of non-equilibrium charge-carrier dynamics in materials by reliably distinguishing between changes in absorption coefficient and refractive index, thereby separating competing processes. This information will help to overcome the limitations of materials for high-power optical devices that owe their properties from dynamics in the ultrafast regime.

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  • 13.
    Richter, Steffen
    et al.
    ELI Beamlines/Fyzikální ústav AV ČR, v.v.i., Za Radnicí 835, 25241 Dolní Břežany, Czech Republic.
    Rebarz, Mateusz
    ELI Beamlines/Fyzikální ústav AV ČR, v.v.i., Za Radnicí 835, 25241 Dolní Břežany, Czech Republic.
    Herrfurth, Oliver
    Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Linnéstr. 5, 04103 Leipzig, Germany.
    Espinoza, Shirly
    ELI Beamlines/Fyzikální ústav AV ČR, v.v.i., Za Radnicí 835, 25241 Dolní Břežany, Czech Republic.
    Schmidt-Grund, Rüdiger
    Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Linnéstr. 5, 04103 Leipzig, Germany; Technische Universität Ilmenau, Institut für Physik, Weimarer Str. 32, 98693 Ilmenau, Germany.
    Andreasson, Jakob
    ELI Beamlines/Fyzikální ústav AV ČR, v.v.i., Za Radnicí 835, 25241 Dolní Břežany, Czech Republic.
    Broadband femtosecond spectroscopic ellipsometry2021In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Review of Scientific Instruments, Vol. 92, no 3Article in journal (Refereed)
    Abstract [en]

    We present a setup for time-resolved spectroscopic ellipsometry in a pump–probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer–sample–compensator–analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump–probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV–3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues. 

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  • 14.
    Schubert, Mathias
    et al.
    Univ Nebraska, NE 68588 USA.
    Knight, Sean Robert
    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.
    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.
    Ruder, Alexander
    Univ Nebraska, NE 68588 USA.
    Stokey, Megan
    Univ Nebraska, NE 68588 USA.
    Korlacki, Rafal
    Univ Nebraska, NE 68588 USA.
    Irmscher, Klaus
    Leibniz Inst Kristallzuchtung, Germany.
    Neugebauer, Petr
    Brno Univ Technol, Czech Republic.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Lund Univ, Sweden.
    Terahertz electron paramagnetic resonance generalized spectroscopic ellipsometry: The magnetic response of the nitrogen defect in 4H-SiC2022In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 120, no 10, article id 102101Article in journal (Refereed)
    Abstract [en]

    We report on terahertz (THz) electron paramagnetic resonance generalized spectroscopic ellipsometry (THz-EPR-GSE). Measurements of field and frequency dependencies of magnetic response due to spin transitions associated with nitrogen defects in 4H-SiC are shown as an example. THz-EPR-GSE dispenses with the need of a cavity, permits independently scanning field and frequency parameters, and does not require field or frequency modulation. We investigate spin transitions of hexagonal (h) and cubic (k) coordinated nitrogen including coupling with its nuclear spin (I = 1), and we propose a model approach for the magnetic susceptibility to account for the spin transitions. From the THz-EPR-GSE measurements, we can fully determine polarization properties of the spin transitions, and we can obtain the k coordinated nitrogen g and hyperfine splitting parameters using magnetic field and frequency dependent Lorentzian oscillator line shape functions. Magnetic-field line broadening presently obscures access to h parameters. We show that measurements of THz-EPR-GSE at positive and negative fields differ fundamentally and hence provide additional information. We propose frequency-scanning THz-EPR-GSE as a versatile method to study properties of spins in solid state materials.

  • 15.
    Smaali, A.
    et al.
    Division des Milieux Ionisés et Lasers, Centre de Développement des Technologies Avancées, Cité 20 août 1956, B. P. 17, Baba Hassen, Algiers 16081, Algeria; Faculté de Physique, Université des Sciences et Technologies Houari Boumediene, BP 32 El Alia 16111 Bab Ezzouar, Algiers, Algeria.
    Abdelli-Messaci, S.
    Division des Milieux Ionisés et Lasers, Centre de Développement des Technologies Avancées, Cité 20 août 1956, B. P. 17, Baba Hassen, Algiers 16081, Algeria.
    Lafane, S.
    Division des Milieux Ionisés et Lasers, Centre de Développement des Technologies Avancées, Cité 20 août 1956, B. P. 17, Baba Hassen, Algiers 16081, Algeria.
    Mavlonov, A.
    School of Physics, University of Electronic Science and Technology of China 610054 Chengdu, China.
    Lenzner, J.
    Felix-Bloch-Institut für Festkörperphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany.
    Richter, Steffen
    ELI Beamlines/Institute of Physics, Czech Academy of Sciences, Za Radnicí 835, 25241 Dolní Břežany, Czech Republic.
    Kechouane, M.
    Faculté de Physique, Université des Sciences et Technologies Houari Boumediene, BP 32 El Alia 16111 Bab Ezzouar, Algiers, Algeria.
    Nemraoui, O.
    Mechatronics, Cape Peninsula University of Technology P.O. Box 1906, Bellville 7535, South Africa.
    Ellmer, K.
    Optotransmitter-Umweltschutz-Technologie e.V. Köpenicker Str. 325 1, D-12555 Berlin, Germany.
    Pulsed laser deposited transparent and conductive V-doped ZnO thin films2020In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 700Article in journal (Refereed)
    Abstract [en]

    ZnO and vanadium-doped ZnO (0.7–4.1 at.%) thin films were deposited onto corning glass substrates by the pulsed laser deposition technique using a KrF excimer laser (λ = 248 nm). The films were deposited at 500 °C under an oxygen pressure of 1 Pa with a laser fluence of 2 J/cm2. The structural, morphological, optical and electrical properties as a function of the dopant atomic concentration were investigated by means of X-ray diffraction, Scanning Electron Microscopy, spectrophotometry, conductivity and Hall measurements. All the doped and undoped films show a preferential orientation along the c-axis with a deterioration at higher doping levels (>4 at. %). Besides, as the doping amount increases the in-plane stress leads to an increase of the c-axis lattice parameter. The films are transparent within the wavelength range 400–1200 nm. The electrical resistivity of the films drops from 8.2 10−3 to 1.3 10−3 Ω cm with an increase in the dopant concentration up to 0.9 at. % and then rises as the dopant level is increased further.

  • 16.
    Stokey, Megan
    et al.
    Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
    Gramer, Teresa
    Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
    Korlacki, Rafał
    Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
    Knight, Sean Robert
    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. NanoLund and Solid State Physics, Lund University, 22100 Lund, Sweden.
    Jinno, Riena
    School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA;Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan.
    Cho, Yongjin
    School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA.
    Xing, Huili Grace
    School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA;Department of Material Science and Engineering, Cornell University, Ithaca, New York 14853, USA.
    Jena, Debdeep
    School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA;Department of Material Science and Engineering, Cornell University, Ithaca, New York 14853, USA.
    Hilfiker, Matthew
    Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. NanoLund and Solid State Physics, Lund University, 22100 Lund, Sweden.
    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.
    Infrared-active phonon modes and static dielectric constants in α-(AlxGa1−x)2O3 (0.18  ≤ x  ≤ 0.54) alloys2022In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 120, no 11, article id 112202Article in journal (Refereed)
    Abstract [en]

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

  • 17.
    Stokey, Megan
    et al.
    Univ Nebraska, NE 68588 USA.
    Korlacki, Rafal
    Univ Nebraska, NE 68588 USA.
    Hilfiker, Matthew
    Univ Nebraska, NE 68588 USA.
    Knight, Sean Robert
    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.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jinno, Riena
    Cornell Univ, NY 14853 USA; Kyoto Univ, Japan.
    Cho, Yongjin
    Cornell Univ, NY 14853 USA.
    Xing, Huili Grace
    Cornell Univ, NY 14853 USA; Cornell Univ, NY 14853 USA.
    Jena, Debdeep
    Cornell Univ, NY 14853 USA; Cornell Univ, NY 14853 USA.
    Oshima, Yuichi
    Natl Inst Mat Sci, Japan.
    Khan, Kamruzzaman
    Univ Michigan, MI 48109 USA.
    Ahmadi, Elaheh
    Univ Michigan, MI 48109 USA.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Nebraska, NE 68588 USA.
    Infrared dielectric functions and Brillouin zone center phonons of alpha-Ga2O3 compared to alpha-Al2O32022In: Physical Review Materials, E-ISSN 2475-9953, Vol. 6, no 1, article id 014601Article in journal (Refereed)
    Abstract [en]

    We determine the anisotropic dielectric functions of rhombohedral alpha-Ga2O3 by far-infrared and infrared generalized spectroscopic ellipsometry and derive all transverse optical and longitudinal optical phonon mode frequencies and broadening parameters. We also determine the high-frequency and static dielectric constants. We perform density functional theory computations and determine the phonon dispersion for all branches in the Brillouin zone, and we derive all phonon mode parameters at the Brillouin zone center including Raman-active, infrared-active, and silent modes. Excellent agreement is obtained between our experimental and computation results as well as among all previously reported partial information from experiment and theory. We also compute the same information for alpha-Al2O3, the binary parent compound for the emerging alloy of alpha-(AlxGa1-x)(2)O-3, and use results from previous investigations [Schubert, Tiwald, and Herzinger, Phys. Rev. B 61, 8187 (2000)] to compare all properties among the two isostructural compounds. From both experimental and theoretical investigations, we compute the frequency shifts of all modes between the two compounds. Additionally, we calculate overlap parameters between phonon mode eigenvectors and discuss the possible evolution of all phonon modes into the ternary alloy system and whether modes may form single-mode or more complex mode behaviors.

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