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  • 1. Arnaudov, B
    et al.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Evtimova, S
    Heuken, M
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hall effect data analysis of GaN n(+)n structures2002In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 234, no 3, 872-876 p.Article in journal (Refereed)
    Abstract [en]

    We develop a model for analysis of Hall effect data of GaN structures composed of sublayers with different thicknesses and contacts placed on the top surface, We analysed the contributions of the conductivity of every sublayer of a planar sample taking into account the fact that the sample sublayers are partially connected in parallel to each other by series resistances formed in areas lying below the contacts from the upper layer. Correction factors, which reduce the contribution of the underlying layers to the measured whole sample conductivity, are obtained from the equations relevant to the respective equivalent circuit.

  • 2. Arnaudov, B
    et al.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Evtimova, S
    Valcheva, E
    Heuken, M
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Multilayer model for Hall effect data analysis of semiconductor structures with step-changed conductivity2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 4Article in journal (Refereed)
    Abstract [en]

    We present a multilayer model for analysis of Hall effect data of semiconductor structures composed of sublayers with different thicknesses and contacts placed on the top surface. Based on the circuit theory we analyze the contributions of the conductivity of every sublayer and derive general expressions for the conductivity and carrier mobility of a multilayer planar sample. The circuit analysis is performed taking into account the fact that the sample sublayers are partially connected in parallel to each other by series resistances formed in areas lying below the contacts from each upper layer. In order to solve the inverse problem of determining the electrical parameters of one of the sublayers, a procedure for analysis of the Hall effect data is proposed. The model is simplified for a structure composed of two layers with the same type of conductivity, and is used to determine the electrical parameters of GaN films grown on relatively thick GaN buffers.

  • 3.
    Arnaudov, B
    et al.
    Faculty of Physics, Sofia University, Sofia, Bulgaria.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Goldys, EM
    Semiconductor Science and Technology Laboratories, Macquarie University, Sydney, Australia.
    Evtimova, S
    Faculty of Physics, Sofia University, Sofia, Bulgaria.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Modeling of the free-electron recombination band in emission spectra of highly conducting n-GaN2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 4Article in journal (Refereed)
    Abstract [en]

    We simulate the spectral distribution of the free-electron recombination band in optical emission spectra of GaN with a free-carrier concentration in the range of 5 x 10(17)-1 x 10(20) cm(-3). The influence of several factors, such as nonparabolicity, electron-electron interaction. and electron-impurity interaction on both the spectral and energy position and the effective gap narrowing are taken into account. The calculated properties of the free-electron-related emission bands are used to interpret the experimental photoluminescence and cathodoluminescence spectra of GaN epitaxial layers.

  • 4. Arnaudov, B.
    et al.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Magnusson, Björn
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Lu, H.
    Schaff, W.J.
    On the nature of the near bandedge luminescence of InN epitaxial layers2005In: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 772, 285-286 p.Article in journal (Refereed)
  • 5. Arnaudov, B
    et al.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Magnusson, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Valcheva, E
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lu, H
    Schaff, WJ
    Amano, H
    Akasaki, I
    Energy position of near-band-edge emission spectra of InN epitaxial layers with different doping levels2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 11Article in journal (Refereed)
    Abstract [en]

    We studied the shape and energy position of near-band-edge photoluminescence spectra of InN epitaxial layers with different doping levels. We found that the experimental spectra of InN layers with moderate doping level can be nicely interpreted in the frames of the "free-to-bound" recombination model in degenerate semiconductors. For carrier concentrations above n>5x10(18) cm(-3) the emission spectra can also be modeled satisfactorily, but a contribution due to a pushing up of nonequilibrium holes over the thermal delocalization level in the valence band tails should be considered in the model. The emission spectra of samples with low doping level were instead explained as a recombination from the bottom of the conduction band to a shallow acceptor assuming the same value of the acceptor binding energy estimated from the spectra of highly doped samples. Analyzing the shape and energy position of the free-electron recombination spectra we determined the carrier concentrations responsible for the emissions and found that the fundamental band gap energy of InN is E-g=692+/-2 meV for an effective mass at the conduction-band minimum m(n0)=0.042m(0).

  • 6.
    Arnaudov, B.
    et al.
    Faculty of Physics, Sofia University, 5 J. Bourchier Blvd, 1164 Sofia, Bulgaria.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Magnusson, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Valcheva, E.
    Faculty of Physics, Sofia University, 5 J. Bourchier Blvd, 1164 Sofia, Bulgaria.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lu, H.
    Department of Electrical Engineering, Cornell University, Ithaka, NY 14583, United States.
    Schaff, W.J.
    Department of Electrical Engineering, Cornell University, Ithaka, NY 14583, United States.
    Amano, H.
    Department of Electrical Engineering, Meijo University, I-501 Shiogamaguchi, Tempaku-ku, Nagoia 468, Japan.
    Akasaki, I.
    Department of Electrical Engineering, Meijo University, I-501 Shiogamaguchi, Tempaku-ku, Nagoia 468, Japan.
    Free-to-bound radiative recombination in highly conducting InN epitaxial layers2004In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 36, no 4-6, 563-571 p.Article in journal (Refereed)
    Abstract [en]

    We present a theoretical simulation of near-band-edge emission spectra of highly conducting n-InN assuming the model of 'free-to-bound' radiative recombination (FBRR) of degenerate electrons from the conduction band with nonequilibrium holes located in the valence band tails. We also study experimental photoluminescence (PL) spectra of highly conducting InN epitaxial layers grown by MBE and MOVPE with electron concentrations in the range (7.7 × 1017-6 × 1018) cm-3 and find that the energy positions and shape of the spectra depend on the impurity concentration. By modeling the experimental PL spectra of the InN layers we show that spectra can be nicely interpreted in the framework of the FBRR model with specific peculiarities for different doping levels. Analyzing simultaneously the shape and energy position of the InN emission spectra we determine the fundamental bandgap energy of InN to vary between Eg = 692 meV for effective mass mn0 = 0.042m0 and Eg =710 meV for mn0 = 0.1m0. © 2004 Elsevier Ltd. All rights reserved.

  • 7.
    Arnaudov, B.
    et al.
    Faculty of Physics, Sofia University, 1164 Sofia, Bulgaria.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Valassiades, O.
    Aristoteles Univ. of Thessaloniki, Solid State Physics Section, 54124 Thessaloniki, Greece.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Evtimova, S.
    Faculty of Physics, Sofia University, 1164 Sofia, Bulgaria.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Heuken, M.
    AIXTRON AG, D-52072 Aachen, Germany.
    Magnetic-field-induced localization of electrons in InGaN/GaN multiple quantum wells2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, no 13, 2590-2592 p.Article in journal (Refereed)
    Abstract [en]

    A study was performed on the magnetic-field-induced localization of electrons in InGaN/GaN multiple quantum wells (MQW). A stepwise behavior of both the Hall coefficient and magnetoresistivity was observed. The peculiarities were explained by a magnetic-field-induced localization of electrons in a two-dimensional (2D) potential relief of the InGaN MQW.

  • 8.
    Arwin, Hans
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Schubert, Mattias
    Department of Electrical Engineering University of Nebraska.
    Figge, S
    Hommel, D
    Haskell, B A
    Fini, P T
    Nakamura, S
    Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN2005In: ICSN-6,2005, 2005Conference paper (Other academic)
  • 9.
    Darakchieva, V.
    et al.
    IFM Linköpings universitet.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Schubert, Mattias
    Fakultät für Physik und Geowissenshaften Universität Leipzig.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Amano, H.
    Dept of Electrical and Electronic Engineering Meijo University, Japan.
    Akasaki, I.
    Dept. of Electrical and Electronic Engineering Meijo University, Japan.
    Strain evolution and phonons in AlN/GaN superlattices2003Article in journal (Refereed)
    Abstract [en]

    AlN/GaN superlattices (SLs) with different periods grown on GaN buffer layers were studied by infrared spectroscopic ellipsometry (IRSE), Raman scattering (RS) and high-resolution reciprocal space mapping (RSM). The lattice parameters and the degree of strain in the GaN buffer and the SL constituents were determined. Phonon modes originating from the buffer layer and the SL sublayers were identified and their frequency shifts were correlated with the strain state of the films.

  • 10.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Strain evolution in high temperature AlN buffer layers for HVPE-GaN growth2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, 59-64 p.Article in journal (Refereed)
    Abstract [en]

    High temperature AlN buffer layers are deposited on a-plane sapphire by reactive magnetron sputtering. The effect of the buffer thickness on the AlN structural properties and surface morphology are studied in correlation with the subsequent hydride vapour phase epitaxy of GaN. A minimum degree of mosaicity and screw dislocation density is determined for a 50 nm thick AlN buffer. With increasing the AlN thickness, a strain relaxation occurs as a result of misfit dislocation generation and higher degree of mosaicity. A blue shift of the E-1(TO) frequency evaluated by means of infrared reflection spectroscopy is linearly correlated with an increase in biaxial compressive stress in the films through the IR stress factor k(E1)(b) = 2.57 +/- 0.26 cm(-1) GPa(-1).

  • 11.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology.
    Tungasmita, S
    Wagner, G
    Kasic, A
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Strain-related structural and vibrational properties of thin epitaxial AIN layers2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 4, 045411- p.Article in journal (Refereed)
    Abstract [en]

    The effect of film thickness on the strain and structural properties of thin epitaxial AIN films has been investigated by high resolution x-ray diffraction techniques and transmission electron microscopy. As a result a sublayer model of the degree of strain and related defects for all films is proposed. A sublayer with low defect density and a strain gradient is found to be present in all films and it reaches a maximum thickness of 65 nm. The films are compressively strained and the strain relaxation after a thickness of 65 nm is shown to be accompanied by misfit dislocation generation and increase of the mosaic tilt. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sublayer model has been successfully applied to the analysis of the ellipsometry data through model calculations of the infrared dielectric function which confirm the sublayer model. It is found that the strain gradient results in a gradient of the phonon mode frequencies and broadening parameter. The initial strain relaxation in the films leads to narrowing of the observable infrared modes, while further strain relaxation broadens the modes when substantial defect generation occurs.

  • 12.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Einfeldt, S.
    Hommel, D
    Lourdudoss, S.
    Phonons in strained AlGaN/GaN superlattices2007In: 6th International Symposium on Blue Laser and Light Emitting Diodes,2006, Physica Status Solidi, vol C4: WILEYVCH Verlag GmbH & Co. KGaA , 2007, 170- p.Conference paper (Refereed)
  • 13.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Deformation potentials of the E-1(TO) mode in AlN2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 13, 2302-2304 p.Article in journal (Refereed)
    Abstract [en]

    The deformation potentials of the E-1(TO) mode in AlN are experimentally determined by combining infrared reflection spectroscopy and x-ray diffraction measurements and using a reported value of the Raman-stress factor for hydrostatically stressed bulk AlN. The deformation potentials are found to strongly depend on published stiffness constants of AlN. A comparison with earlier theoretically calculated values of the deformation potentials is made. (C) 2002 American Institute of Physics.

  • 14.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Valcheva, E.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Heuken, M.
    Aixtron AG, D-52072 Aachen, Germany.
    Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 82, no 5, 703-705 p.Article in journal (Refereed)
    Abstract [en]

    The lattice parameters of GaN layers grown on a-plane sapphire were investigated. The hydride vapor phase epitaxy and metalorganic vapor phase epitaxy were used for the determination of parameters. The strain anisotropy was found to have different values in the films and obtained values of parameters were grouped around two values.

  • 15.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology.
    Valcheva, E
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M
    Lu, H
    Schaff, W.J.
    Deformation potentials of the E1 (TO) and E2 modes of InN2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 84, no 18, 3636-3638 p.Article in journal (Refereed)
    Abstract [en]

    The determination of deformation potentials of E1(TO) and E 2 modes of InN were discussed. The deformation potentials were evaluated for two sets of stiffness constants using x-ray diffraction, IR spectroscopic ellipsometry (IRSE), Raman scattering, and Grüneisen parameter values. The InN layer were grown on GaN buffer layers on (0001) sapphire by molecular beam epitaxy. It was found that the strain-free values of the InN E1(TO) mode was 477.9 cm-1 and 491.9 cm -1 for the E2 modes.

  • 16.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Valcheva, E.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M.
    Fak. F. Physik and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Bundesmann, C.
    Fak. F. Physik and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Lu, H.
    Department of Electrical Engineering, Cornell University, Ithaca, NY 14853, United States.
    Schaff, W.J.
    Department of Electrical Engineering, Cornell University, Ithaca, NY 14853, United States.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Infrared ellipsometry and Raman studies of hexagonal InN films: Correlation between strain and vibrational properties2004In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 36, no 4-6, 573-580 p.Article in journal (Refereed)
    Abstract [en]

    The vibrational properties of InN films with different strain have been studied using Infrared ellipsometry and Raman scattering spectroscopy. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and the strain-free frequencies of the InN E1(TO) and E2 modes. The LO phonons and their coupling to the free-carrier plasmon excitations are also discussed in relation to the carrier concentration in the films. © 2004 Elsevier Ltd. All rights reserved.

  • 17.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Schubert, M
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Figge, S
    Hommel, D
    Haskell, BA
    Fini, PT
    Nakamura, S
    Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN2006In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, no 7, 1594-1598 p.Article in journal (Refereed)
    Abstract [en]

    Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a-plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A,(TO) mode. These results are compared with previous theoretical and experimental findings and discussed.

  • 18.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ashkenov, N.
    Fak. fur Phy. and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Schubert, M.
    Fak. fur Phy. and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
    Residual strain in HVPE GaN free-standing and re-grown homoepitaxial layers2003In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 195, no 3, 516-522 p.Article in journal (Refereed)
    Abstract [en]

    The lattice parameters of as-grown hydride vapor phase epitaxy GaN layers on sapphire, free-standing layers after the substrate lift-off, and homoepitaxial layers grown on the free-standing layers are measured. The in-plane and out-of-plane strains are calculated. It is found that the substrate removal leads to strain relaxation in the crack-free GaN free-standing layers to a certain extent. A small increase of the strain in the GaN homoepitaxial layers compared to the free-standing layers is observed. Cathodoluminescence (CL) spectroscopy and imaging, photoluminescence (PL) and Raman measurements are used as complementary tools in the residual strain analysis.

  • 19.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ashkenov, N.
    Schubert, M.
    Structural characteristics and lattice parameters of hydride vapor phase epitaxial GaN free-standing quasisubstrates2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 1, 013517- p.Article in journal (Refereed)
    Abstract [en]

    We have studied the lattice parameters of hydride vapor phase epitaxy (HVPE)-GaN quasisubstrates in relation to their structural properties. Layers grown on single-layer metalorganic vapor phase epitaxy (MOVPE) templates and on epitaxial lateral overgrown MOVPE templates are characterized by Raman scattering, high-resolution x-ray diffraction, and reciprocal space mapping. The strain relaxation in the films versus their thickness was found to proceed similarly in the GaN samples grown using the two types of templates but the strain saturates at different nonzero levels. The lattice parameters of relatively thin HVPE-GaN free-standing quasisubstrates indicate that no total strain relaxation is achieved after the sapphire removal. The lattice parameters of the thick quasisubstrates grown on different templates are not affected by the separation process and are found to have values very close to the reference strain-free lattice parameters of GaN powder. © 2005 American Institute of Physics.

  • 20.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M.
    Optical phonons in a-plane GaN under anisotropic strain2008In: Group-III nitrides with nonpolar surfaces: growth, properties and devices / [ed] Tanya Paskova, Wiley , 2008, 1, 219-253 p.Chapter in book (Other academic)
    Abstract [en]

    This is the first monograph to discuss in detail the current stage of development of nonpolar nitrides, with specific emphasis on the three main topics of crystal growth, properties and device studies. World–class researchers summarize their own recent achievements in their respective fields of expertise, covering both nonpolar and semipolar nitride materials. The bulk of the discussion in each chapter is related to the physical properties of the material obtained by the respective technique, in particular, defect density and properties of the defects in nonpolar nitrides. In addiiton, the optical and vibrational properties are also addressed in several chapters, as is progress in heterostructures, quantum wells and dots based on the AlGaN/GaN and the InGaN/GaN systems. Finally, an outlook of the application areas of the differently grown materials is presented in most chapters, together with the capabilities and limitations of the respective growth approaches used.

  • 21.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Schubert, M.
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hommel, D.
    Off, J.
    Scholz, F.
    Heuken, M.
    Haskell, B.A.
    Fini, P.T.
    Speck, S.J.
    Nakamura, S.
    Anisotropic strain and phonon deformation potentials in GaN2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 19, 195217- p.Article in journal (Refereed)
    Abstract [en]

    We report optical phonon frequency studies in anisotropically strained c -plane- and a -plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E1 (TO), E1 (LO), and E2 phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c E1 (TO), c E1 (LO), and c E2 are determined. A distinct correlation between anisotropic strain and the A1 (TO) and E1 (LO) frequencies of a -plane GaN films reveals the a A1 (TO), b A1 (TO), a E1 (LO), and b E1 (LO) phonon deformation potentials. The a A1 (TO) and b A1 (TO) are found to be in very good agreement with previous results from Raman experiments. Our a A1 (TO) and a E1 (LO) phonon deformation potentials agree well with recently reported theoretical estimations, while b A1 (TO) and b E1 (LO) are found to be significantly larger than the theoretical values. A discussion of the observed differences is presented. © 2007 The American Physical Society.

  • 22.
    Darakchieva, Vanya
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Schubert, M.
    Fak. für Phys./Geowiss., Iniversität Leipzig, 04103 Leipzig, Germany.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Kasic, A.
    Tungasmita, Sukkaneste
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Generalized infrared ellipsometry study of thin epitaxial AlN layers with complex strain behavior2003Conference paper (Refereed)
    Abstract [en]

    The effect of film thickness on the strain and structural properties of thin epitaxial AlN films has been investigated, and a sub-layer model of the degree of strain and related defects for all films is suggested. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sub-layer model has been successfully applied to the analysis of the ellipsometry data trough model calculations of the infrared dielectric function. © 2003 Elsevier B.V. All rights reserved.

  • 23.
    Darakchieva, Vanya
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Valcheva, E.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Schubert, M.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Amano, H.
    Akasaki, I.
    Phonon mode behavior in strained wurtzite AlN/GaN superlattices2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 11, 115329- p.Article in journal (Refereed)
    Abstract [en]

    We have studied phonons in AlN/GaN superlattices with different periods but a constant well-to-barrier ratio using a combination of infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The strain evolution in the superlattice structures is assessed by high-resolution x-ray diffraction and reciprocal space mapping. We have identified E1(TO), A 1(LO) and E2 localized, and E1(LO) and A 1(TO) delocalized superlattice modes. The dependencies of their frequencies on in-plane strain are analyzed and discussed, and the strain-free frequencies of the superlattice modes are estimated. A good agreement between theory and experiment is found in the case of GaN localized modes, while large deviations between theoretically estimated and experimentally determined frequency shifts are observed for the AlN localized modes. The delocalization effect on the A1(TO) and E1(LO) phonons, as well as the free-carrier effect on the E1(LO) phonon are also discussed. ©2005 The American Physical Society.

  • 24. Evtimova, S
    et al.
    Arnaudov, B
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Heuken, M
    Effect of carrier concentration on the microhardness of GaN layers2003In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 14, no 10-12, 771-772 p.Article in journal (Refereed)
    Abstract [en]

    The paper presents a microhardness study of thick crack-free hydride vapor phase epitaxial GaN layers (not intentionally doped), and of thin metal-organic vapor phase epitaxial (MOVPE) GaN layers (undoped and Si-doped), grown on sapphire. A Vickers indentation method was used to determine the microhardness under applied loads up to 2 N. An increase in the microhardness was observed with decreasing carrier concentration and increasing mobility. A dip at an indentation depth of about 0.75 mum is observed in the microhardness profile in the MOVPE films, and is correlated with peculiarities in the spatially resolved cathodoluminescence spectra. The relationship between the mechanical and electrophysical parameters is discussed. (C) 2003 Kluwer Academic Publishers.

  • 25. Figge, S
    et al.
    Bottcher, T
    Dennemarck, J
    Kroger, R
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hommel, D
    Optoelectronic devices on bulk GaN2005In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, no 1, 101-106 p.Article in journal (Refereed)
    Abstract [en]

    The homoeptaxial fabrication of GaN-based devices has advantages against heteroepitaxial realization on substrates such as sapphire or SiC, since heteroepitaxy implies a lot of problems like lattice mismatch, different thermal expansion coefficients, and needs an extensive optimization of the growth at the heterointerface. In this paper we will discuss GaN-based light-emitting devices grown by homoepitaxy in comparison to devices grown on sapphire. A special emphasis is laid on the pretreatment of the GaN substrate and the device characteristics on different substrates. In detail will be discussed the advantages of the higher thermal conductivity of GaN and how this effects the device performance. (c) 2005 Elsevier B.V. All rights reserved.

  • 26. Gelhausen, O
    et al.
    Phillips, MR
    Goldys, EM
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Strassburg, M
    Hoffmann, A
    Dissociation of H-related defect complexes in Mg-doped GaN2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 12Article in journal (Refereed)
    Abstract [en]

    Post-growth annealing and electron beam irradiation during cathodoluminescence were used to determine the chemical origin of the main optical emission lines in moderately and heavily Mg-doped GaN. The 3.27 eV donor-acceptor pair (DAP) emission line that dominates the emission spectrum in moderately Mg-doped (p-type) GaN was found to be strongly reduced by electron irradiation and of different chemical origin than the DAP at a similar energetic position in Si-doped (n-type) GaN. These results suggest that the acceptor responsible for the 3.27 eV DAP emission in Mg-doped GaN is Mg,and that the donor (20-30 meV) is hydrogen-related, possibly a (V-N-H) complex. This complex is dissociated either by electron irradiation or thermal annealing in N-2 or O-2 atmosphere. We found that upon electron irradiation, a deeper emission line (centered at 3.14 eV) emerged, which was assigned to a DAP consisting of the same Mg acceptor level and a deeper donor (100-200 meV) with a similar capture cross section as the donor in the 3.27 eV emission. Moreover, two different deep donor levels at 350+/-30 and 440+/-40 meV were identified as being responsible for,the blue band (2.8-3.0 eV) in heavily Mg-doped GaN. The donor level at 350+/-30 meV was strongly affected by electron irradiation and attributed to a H-related defect.

  • 27.
    Goldys, EM
    et al.
    Macquarie Univ, Div Informat & Commun Sci, N Ryde, NSW, Australia Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
    Godlewski, M
    Macquarie Univ, Div Informat & Commun Sci, N Ryde, NSW, Australia Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Characterization of red emission in nominally undoped hydride vapor phase epitaxy GaN2001In: MRS Internet journal of nitride semiconductor research, ISSN 1092-5783, E-ISSN 1092-5783, Vol. 6, no 1, art. no.-1 p.Article in journal (Refereed)
    Abstract [en]

    We report characterization of the red emission band in hydride vapor phase epitaxial GaN using cathodoluminescence spectroscopy and imaging and time-resolved photoluminescence. The observed properties of the emission are consistent with recombination of excitons bound at close donor-acceptor pairs. The time evolution of the emission signal during electron beam irradiation supports the association of the red emission with charged centres.

  • 28. Kröger, R.
    et al.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Figge, S.
    Hommel, D.
    Rosenauer, A.
    Defect structure of a-plane GaN grown by hydride and metal-organic vapor phase epitaxy on r-plane sapphire2007In: Proc. of the International Workshop on Nitride Semiconductors IWN2006,2006, Physica Status Solidi C, vol. 4: WILEYVCH Verlag GmbH & Co. KGaA , 2007, 2564- p.Conference paper (Refereed)
    Abstract [en]

      

  • 29. Leon, R
    et al.
    Ibanez, J
    Marcinkevicius, S
    Siegert, J
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chaparro, S
    Navarro, C
    Johnson, SR
    Zhang, YH
    Defect states in red-emitting InxAl1-xAs quantum dots2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 8Article in journal (Refereed)
    Abstract [en]

    Optical and transport measurements carried out in pn diodes and Schottky barriers containing multilayers of InAlAs quantum dots embedded in AlGaAs barriers show that while red emission from quantum dot (QD) states is obtained at similar to1.8 eV, defect states dominate the optical properties and transport in these quantum dots. These defects provide nonradiative recombination paths, which shortens the carrier lifetimes in QD's to tens of picoseconds (from similar to1 ns) and produce deep level transient spectroscopy (DLTS) peaks in both p and n type structures. DLTS experiments performed with short filling pulses and bias dependent measurements on InAlAs QD's on n-AlGaAs barriers showed that one of the peaks can be attributed to either QD/barrier interfacial defects or QD electron levels, while other peaks are attributed to defect states in both p and n type structures.

  • 30. Leon, R
    et al.
    Nadeau, J
    Evans, K
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Electron irradiation effects on nanocrystal quantum dots used in bio-sensing applications2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 6, 3186-3192 p.Article in journal (Refereed)
    Abstract [en]

    Effects of low energy electron irradiation (5-30 keV) on some of the optical properties of CdSe nanocrystals are examined. Degradation in luminescence intensities are measured and compared for inorganic nanocrystals coated in trioctylphosphine oxide (TOPO) and biologically compatible CdSe nanocrystals coated in mercaptoacetic acid (MAA), as well as CdSe-MAA nanocrystals conjugated with the protein Streptavidin. Electron beam effects are investigated using the technique of cathodolu-minescence, which is seen to induce significant degradation in nanocrystal related fluorescence in all nanocrystals. Varying beam energy and sample temperatures showed faster degradation at cryogenic temperatures and a higher susceptibility to low beam energies in protein conjugated nanocrystals.

  • 31.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Wagner, Matthias
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Defects in Gallium Nitride1999In: International Workshop on Materials Science,1999, Proc. of the International Workshop on Materials Science 99, ed. by F. F. Bekker et al., Vol. 1: Hanoi National University Publishing House , 1999, 28- p.Conference paper (Refereed)
  • 32.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    The 3.466 eV Bound Exciton in GaN2001In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 228, no 2, 489-492 p.Article in journal (Refereed)
    Abstract [en]

     We discuss the available optical data for the 3.466 eV bound exciton in GaN, which has been a controversial issue in the recent literature. We conclude that the experimental results are only consistent with the identification as an exciton bound at a neutral acceptor with a spin-like bound hole. The chemical identity is still not clear.

  • 33.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, JP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Kamiyama, S
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Iwaya, M
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Amano, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Akasaki, I
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Photoluminescence of excitons in InxGa1-xN/InyGa1-yN multiple quantum wells2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, 161-166 p.Article in journal (Refereed)
    Abstract [en]

    We report on a detailed study of excitons in InxGa1-xN/InyGa1-yN multiple quantum wells (MQWs) with an In composition x in the QWs of about 0.1, and a small In composition y in the barrier of 0.01-0.02. The MOVPE growth procedure was optimized to allow growth without In segregation. The InyGa1-yN barriers had a Si doping of about 5 x 10(18) cm(-3) . The low temperature photoluminescence spectra show two sets of exciton-like spectra with quite different properties. The lower energy emission has a small thermal activation energy (about 5 meV), and thus disappears at elevated temperatures, it is not observed at room temperature. The higher energy exciton state has a decay time of about 5 ns, while the lower energy process is much slower. We have also done preliminary studies on samples where the MQW region is situated in a p-n junction field, with semi-transparent contacts, to study the effects of varying the bias across the MQW structure. The combination of optical data can e interpreted in terms of a substantial potential gradient across the MQW region for both samples. The conclusion is that probably only one QW is emitting at low T (and no bias), and the second lower energy PL peak originates from a shallow notch in the conduction band at the interface between the thick GaN buffer layer and the first Ga(In)N barrier.

  • 34.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Figge, S
    Dennemarck, J
    Hommel, D
    The dominant shallow 0.225 eV acceptor in GaN2006In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, no 7, 1604-1608 p.Article in journal (Refereed)
    Abstract [en]

    We have studied the optical signatures of the Mg acceptor in GaN, using samples that are doped with Mg during MOCVD growth. In order to reduce the defect density in the material and thus achieve narrow linewidths in optical spectra we have used thick HVPE grown GaN layers as templates in the MOCVD growth. The photoluminescence (PL) spectra show two acceptor-related bound exciton peaks at 3.466 eV and 3.455 eV respectively. In the lower photon energy range the 3.27 eV emission with its LO-phonon replicas is dominant, riding on a broad background emission peaking at about 3.1 eV. These results, together with previous data in the literature, indicate that there are two acceptors in Mg-doped GaN, one dominating the optical spectra (the 3.466 eV and the 3.27 eV emissions) and another related to the 3.455 eV and the 3.1 eV emissions. We suggest that the latter is related to the Mg acceptor, while the former is a H-related complex, not necessarily involving Mg.

  • 35.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Malinauskas, T
    Jarasiunas, K
    Gibart, P
    Beaumont, B
    Time-resolved spectroscopy of excitons bound at shallow neutral donors in HVPE GaN2006In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, 482-485 p.Article in journal (Refereed)
    Abstract [en]

    Time-resolved photo luminescence (TRPL) data for temperatures 2-150 K are presented for two thick HVPE samples grown in two different laboratories. The samples both have residual O and Si shallow donor concentrations in the 10(16)cm(-3) range. The radiative decay time for neutral donor-bound excitons (DBEs) related to these donors is found to be about 300 ps. The decay of the DBEs at longer decay times is found to be related to feeding from the free exciton-polariton states. At elevated temperatures the decay of the DBE is very similar to the free exciton decay. (c) 2006 Elsevier B.V. All rights reserved.

  • 36.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Haradizadeh, H
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Valcheva, E
    Darakchieva, Vanya
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Arnaudov, B
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kamiyama, S
    Iwaya, M
    Amano, H
    Akasaki, I
    Optical investigation of AlGaN/GaN quantum wells and superlattices2004In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 10, 2251-2258 p.Article in journal (Refereed)
    Abstract [en]

    We report a detailed optical study of several sets of multiple quantum wells (MQWs) in the AlGaN/GaN system, as well as AlN/GaN superlattice (SL) structures. In this study all materials were grown by MOCVD, as opposed to most previous studies where MBE was employed. In undoped MQWs discrete photoluminescence (PL) peaks related to discrete well width fluctuations by one full c lattice parameter are clearly observed. In doped samples this effect appears to be screened. While the recombination process in undoped samples is excitonic, in MQWs doped with Si above about 5 x 10(18) cm(-3) free electrons (a 2DEG) are dominant, and the PL process is a free electrons-localized hole transition at low temperatures. The hole localization prevails up to very high n-doping, as was previously observed in bulk GaN. The hole localization is demonstrated via several experiments, including results on PL transient decay times and LO phonon coupling. Near surface band bending, due mainly to dopant depletion in doped structures or interaction with surface states in case of higher Al content in barriers, influences the distribution of electron filling among the QWs, making a detailed modeling of the spectral shape somewhat ambiguous. It is found that AlN barriers promote a strong room temperature PL signal from the QWs, as opposed to the case with AlGaN barriers.

  • 37.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Hai, P.N.
    Hai, P.N..
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Amano, H.
    Department of Materials Science and Engineering, High Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Akasaki, I.
    Department of Materials Science and Engineering, High Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Optical characterization of III-nitrides2002Conference paper (Refereed)
    Abstract [en]

    Recent developments in material properties of GaN and related heterostructure combinations are reviewed, with emphasis on optical data. We discuss recent polarized photoluminescence (PL) data on the free excitons in GaN, obtained from thick HVPE grown layers. The exchange splitting constant is found to be about 0.6 meV, a more accurate value than previous suggestions. The PL signatures of shallow donors and acceptors, i.e. the bound excitons, are discussed and tentatively identified. Intrinsic point defects are discussed in terms of stability and experimental signatures. Quantum well structures in the InGaN/GaN and GaN/AlGaN systems are briefly discussed, with emphasis on localization of carriers and excitons. © 2002 Published by Elsevier Science B.V.

  • 38.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Toropov, A.A.
    Choubina, Tatiana
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Kawashima, T.
    Amano, H.
    Akasaki, I.
    Usui, A.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Properties of dopants and defects in GaN from bound exciton spectra2008In: Meijo International Symposium on Nitride Semiconductors 2008,2008, 2008Conference paper (Other academic)
  • 39.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Amano, H.
    Akasaki, I.
    Figge, S.
    Hommel, D.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Usiui, A.
    Mg related acceptors in GaN2010In: Phys. Status Solidi C 7, 2010, 1850- p.Conference paper (Refereed)
  • 40.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Bergman, JP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Iwaya, M
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Nitta, S
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Amano, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Akasaki, I
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Optical characterization of InGaN/GaN MQW structures without in phase separation2001In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 228, no 1, 157-160 p.Article in journal (Refereed)
    Abstract [en]

    Photoluminescence and cathodoluminescence spectroscopies are used to investigate the properties of the band edge emission of InGaN/(In)GaN multiple quantum well (MQW) structures which do not show evidence of phase separation in high resolution electron microscopy. The data still show a clear low energy peak in the spectra. about 0.1 eV below the main exciton peak. Possible interpretations of this second peak are discussed.

  • 41.
    Monemar, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    IFM Linköpings universitet.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kasic, Aleksander
    Growth of thick GaN layers by hydride vapor phase epitaxy2005In: Journal of Ceramic Processing Research, ISSN 1229-9162, Vol. 6, no 2, 153-162 p.Article in journal (Refereed)
    Abstract [en]

    In this paper we describe recent experimental work on the growth of thick GaN layers (up to >300 μm) on sapphire with hydride vapour phase epitaxy (HVPE), the removal of the sapphire substrate by the laser liftoff technique, and the properties of these thick GaN layers. Two different growth setups were used, one horizontal and one vertical system. Specific conditions in the growth procedure, like gas flow pattern, growth rate and the use of buffer layers, strongly influence the properties of the grown layers. Important defect problems are cracking (both during and after growth), and the generation of dislocations and surface pits. A large bowing is also observed for thick layers, depending very much on the properties of the initially grown material. For growth of thick layers excessive parasitic growth of GaN upstream of the substrate has to be avoided. Laser liftoff is demonstrated to be a feasible process to remove the sapphire substrate, causing the GaN surface bowing to decrease and revert from convex to concave. The threading dislocation density of 300 μm thick GaN layers is found to be about 107 cm-2, rather independent of the type of buffer layer employed. It reduces further in thicker layers. The pit density varies with growth conditions, it can be reduced if the parasitic growth is avoided. The bowing is a serious problem, since the layers have to be polished to make the surface epi-ready. The XRD rocking curve widths measured seem to correlate with the bowing of the layers, a reduction by about a factor two is often observed when the substrate is removed. Optical characterisation like photoluminescence (PL) and ir spectroscopic ellipsometry (IRSE) is very useful to monitor strain in the layers, as well as impurities and point defects. Residual shallow donors are related to O and Si, shallow acceptors are mainly of intrinsic origin, i.e. complexes with the Ga vacancy.

  • 42.
    Paskov, Plamen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Iwaya, M.
    Kamiyama, S.
    Amano, H.
    Akasaki, I.
    Photoluminescence of GaN/AlN superlattices grown by MOCVD2005In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 2, 2345-2348 p.Article in journal (Refereed)
  • 43.
    Paskov, Plamen
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Darakchieva, Vanya
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Anisotropy of the in-plane strain in GaN grown on A-plane sapphire2002In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 234, no 3, 892-896 p.Article in journal (Refereed)
    Abstract [en]

    A comparative study of GaN layer grown by hydride vapour phase epitaxy on A-plane sapphire before and after removal of the substrate is presented. A large anisotropy of the in-plane strain in the as-grown sample is revealed by X-ray diffraction measurements and polarized photoluminescence. The strain anisotropy is found to modify the selection rules for the transitions leading to a splitting of the optically active states of the A and B excitons. Almost complete strain relaxation and recovery of the optical isotropy in the (0001) plane is observed in the free-standing layer.

  • 44.
    Paskov, Plamen
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Kamiyama, S.
    Amano, H.
    Akasaki, I.
    Photoluminescence study of near-surface GaN/AlN superlattices2008In: Proceedings of SPIE - The International Society for Optical Engineering, 2008, 68940G1- p.Conference paper (Refereed)
    Abstract [en]

    We report on the emission properties of GaN/AlN superlattices (SLs) grown by metalorganic chemical vapor deposition on a thick GaN layer. Nominally undoped and Si-doped SL structures with the well/barrier thickness ratio 3:1 and different SL periods are investigated. It is found that in these SLs without capping layer the energy position, intensity and linewidth of the emission are determined by the interplay of the built-in polarization field, the depletion field arising from the pinning of the Fermi level at the surface, and the screening of the electric field in the quantum well due to the both the polarization-induced two-dimension electron gas (2DEG) and the photo-generated carriers. A non-uniform equilibrium electron distribution and an electron accumulation at the bottom AlN/GaN interface are evidenced by the observed recombination of the 2DEG with the photo-excited holes occurring below the GaN bandgap.

  • 45.
    Paskov, Plamen
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Preble, E.A.
    Hanser, A.D.
    Evans, K.R.
    Optical characterization of bulk GaN substrates with c-, a-, and m-plane surfaces2008Conference paper (Refereed)
  • 46.
    Paskov, Plamen
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Anisotropy of the free exciton emission in GaN grown on a-plane sapphire2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, 75-79 p.Article in journal (Refereed)
    Abstract [en]

    The influence of the anisotropic in-plane strain on the optical response of GaN layers grown on a-plane sapphire is investigated. A splitting of the G5 states of the A and B free excitons into two components, polarized parallel and perpendicular to the strain direction, is observed. The experimental results are discussed in the framework of the effective exciton Hamiltonian formalism.

  • 47.
    Paskov, Plamen
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Internal structure of free excitons in GaN2001In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 228, no 2, 467-470 p.Article in journal (Refereed)
    Abstract [en]

    Polarized photoluminescence is used to study the fine structure of free excitons in thick GaN layers grown on differently oriented sapphire substrates. The singlet-triplet splitting of the A exciton is measured and the exchange interaction constant in GaN is determined. For the samples grown on the a-plane sapphire, splitting of the A and B excitons induced by the uniaxial in-plane stress is also observed.

  • 48.
    Paskov, Plamen
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Polarisation dependent spectroscopy of the near bandgap emission in free-standing GaN2004In: 2003 MRS Fall Meeting,2003, 2004, Y6.1.1- p.Conference paper (Refereed)
  • 49.
    Paskov, Plamen
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Polarized photoluminescence of exciton-polaritons in free-standing GaN2004In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 4, 678-685 p.Article in journal (Refereed)
    Abstract [en]

    We report on the polarization properties of the exciton-polariton modes in GaN. The dispersion curves and the expected emission lineshape of polaritons for all polarization configurations are calculated taking into account the spatial dispersion and the simultaneous exciton-photon coupling of all optically active states. An experimental study of the exciton-polariton luminescence in a free-standing GaN layer is also performed. The spectra reveal a clear difference between the emissions polarized perpendicular and parallel to the c-axis of the crystal. The experimental results are discussed in terms of optical selection rules and population of the polariton states. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 50.
    Paskov, Plamen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Paskova, Tanja
    Linköping University, Department of Physics, Chemistry and Biology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Polarized photoluminescence study of free and bound excitons in free-standing GaN2004Article in journal (Refereed)
    Abstract [en]

    A study of the polarization properties of the exciton emission in GaN is presented. Photoluminescence measurements are performed for light propagation perpendicular to the c axis of a free standing layer grown by hydride vapor phase epitaxy. Emission from different polariton branches of the Γ5 and Γ1, free exciton states are identified for the E ⊥ c and E∥c polarizations, respectively. The mixed-mode transverse-longitudinal state of the A exciton is also observed in the E∥c polarized spectra. Donor-bond excitons involving a hole from the A and B valence bands are clearly distinguished and are found to follow the optical selection rules of the free excitons. The temperature dependence of the emission intensities is also investigated and the exciton thermalization processes for both polarizations are discussed.

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