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  • 1.
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Spectroscopic ellipsometry for characterization and monitoring of organic layers2001In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 188, no 4, 1331-1338 p.Article in journal (Refereed)
    Abstract [en]

    The thickness resolution and the in situ advantage of ellipsometry make this optical technique suitable for studies of thin organic layers, especially those of biological interest. With state of the art methodology it is possible to perform monolayer spectroscopy, e.g. of a protein layer at a solid/ liquid interface and also to resolve details in the kinetics of layer formation. Furthermore, complicated microstructures, like porous silicon layers, can be characterized and protein adsorption can be monitored in porous layers providing information about pore filling and penetration depths of protein molecules of different size and type. Quantification of adsorption and determination of microstructural parameters of thin organic layers on planar surfaces and in porous layers are of large interest in areas like biomaterials, basic studies of surface-based biointeraction and for biosensor development. In this report we review the use of spectroscopic ellipsometry for studies of organic layers including protein adsorption and protein monolayer spectroscopy. Included is also a discussion about possibilities for in situ spectroscopic monitoring of engineering of multilayer systems based on macromolecules.

  • 2.
    Arwin, Hans
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Gavutis, M
    Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden Vilnius State Univ, Dept Phys, Vilnius, Lithuania Univ Nebraska, Ctr Microelect & Opt Mat Res, Lincoln, NE 68588 USA Univ Nebraska, Dept Elect Engn, Lincoln, NE 68588 USA.
    Gustafsson, J
    Schultzberg, M
    Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden Vilnius State Univ, Dept Phys, Vilnius, Lithuania Univ Nebraska, Ctr Microelect & Opt Mat Res, Lincoln, NE 68588 USA Univ Nebraska, Dept Elect Engn, Lincoln, NE 68588 USA.
    Zangooie, S
    Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden Vilnius State Univ, Dept Phys, Vilnius, Lithuania Univ Nebraska, Ctr Microelect & Opt Mat Res, Lincoln, NE 68588 USA Univ Nebraska, Dept Elect Engn, Lincoln, NE 68588 USA.
    Tengvall, Pentti
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Protein adsorption in thin porous silicon layers2000In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 182, no 1, 515-520 p.Article in journal (Refereed)
    Abstract [en]

    Porous silicon layers with thicknesses in the range 100-400 nm and average porosities in the range 38-71% were prepared by electrochemical anodization. Variable angle spectroscopic ellipsometry was used to characterize the microstructure of the layers before protein adsorption. In-situ ellipsometry was then employed tr, monitor the kinetics of fibrinogen and human serum albumin adsorption. At steady state new ellipsometric spectra were recorded to determine the total amount of adsorbed protein. Under the experimental conditions used here, the protein molecules were found to adsorb in the outermost part of the porous layer. However, human serum albumin penetrated into the porous silicon matrix at low pH and high porosity. From a methodological point of view it was found that spectroscopic ellipsometry is an appropriate tool for characterization of the microstructure of porous silicon layers and for in-situ monitoring of protein adsorption in such layers including depth profiling.

  • 3.
    Arwin, Hans
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Wang, Guoliang
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Jansson, Roger
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Gas sensing based on ellipsometric measurement on porous silicon2003In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 197, no 2, 518-522 p.Conference paper (Other academic)
    Abstract [en]

    Ellipsometry has sufficient sensitivity for sensor applications and is here used as an optical readout method in a gas sensing system. Porous silicon is used as sensing layers in which vapors of solvents can adsorb and condensate due to capillary effects. A miniaturized multi-beam ellipsometer system is proposed and the concept is demonstrated by measurements on alcohol vapors. Optimization of the sensor system is discussed and improvement of sensitivity and alteration of selectivity by metal deposition in porous silicon layers are presented.

  • 4.
    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).

  • 5.
    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.

  • 6. Godlewski, M
    et al.
    Przybylinska, H
    Bozek, R
    Goldys, EM
    Bergman, Peder
    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 .
    Grzegory, I
    Porowski, S
    Compensation mechanisms in magnesium doped GaN2004In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 2, 216-220 p.Article in journal (Refereed)
    Abstract [en]

    Compensation processes in magnesium doped GaN epilayers and bulk samples are studied. We demonstrate enhancement of potential fluctuations in Mg doped samples, from Kelvin probe atomic force microscopy measurements. Large- and small-scale light emission fluctuations are also demonstrated. Micro-photoluminescence (PL) study indicates an unusual anti-correlation between the intensities of excitonic and defect-related emission processes in p-type doped structures and also the presence of the so-called hot-PL. Hot-PL observed in compensated p-type samples, we relate to the presence of strong potential fluctuations. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 7.
    Gogova, Daniela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Zolnai, Z.
    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.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fast growth of high quality GaN2003In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 200, no 1, 13-17 p.Article in journal (Refereed)
    Abstract [en]

    We have grown bulk-like GaN with a thickness up to 335 μm on 2″ sapphire substrates in a vertical HVPE reactor with a bottom-fed design. A very high growth rate of 250 μm/h is reached with high crystalline quality of the grown material. The low temperature PL spectra show the free A-exciton line at 3.483 eV and rather narrow I2 lines with FWHM of 1–2 meV indicating high crystalline quality and low doping concentration. This HVPE-GaN has the potential to provide lattice-matched and thermally-matched substrates for further epitaxial growth of high quality GaN with a low dislocation density for advanced heterostructure devices.

  • 8.
    Kasic, A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Gogova, Daniela
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    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.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bundesmann, C.
    Institut für Experimentelle Physik II, Universität Leipzig, Leipzig, Germany.
    Schubert, M.
    Institut für Experimentelle Physik II, Universität Leipzig, Leipzig, Germany.
    Micro-Raman scattering profiling studies on HVPE-grown free-standing GaN2004In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 12, 2773-2776 p.Article in journal (Refereed)
    Abstract [en]

    Free-standing GaN of ∼330 μm thickness with low defect density was prepared by hydride vapor-phase epitaxy (HVPE) on sapphire in a vertical atmospheric-pressure reactor and a subsequent laser-induced lift-off process. The structural and optical properties of the material were assessed by various characterization techniques, like X-ray diffraction, photo- and cathodoluminescence, spectroscopic ellipsometry, positron annihilation spectroscopy, and transmission electron microscopy. Here, we focus on μ-Raman scattering profiling studies providing the vertical strain distribution and the evolution of the crystalline quality with increasing layer thickness. Profiles of the free-carrier concentration are obtained from monitoring the LO-phonon plasmon coupled mode. Comparative investigations are performed on the material before and after separation of the sapphire substrate. The GaN material presented here is well capable of serving as a substrate for further homoepitaxial strain-relaxed and crack-free growth needed for fabrication of high-quality III-nitride device heterostructures.

  • 9.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Parlangeli, T
    Eindhoven University of Technology, Netherlands.
    Christianen, PCM
    Eindhoven University of Technology, Netherlands.
    Van Schaijk, R
    Eindhoven University of Technology, Netherlands.
    Maan, JC
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Exciton bleaching in p-type single and double quantum wells: The effects of subband occupation and wave function overlap1997In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 164, no 1, 73-76 p.Article in journal (Refereed)
    Abstract [en]

    We have studied exciton unbinding in empty and p-doped single and double quantum wells, using magneto-photoluminescence excitation measurements. The use of p-type heterostructures allows to discriminate unambiguously between exciton bleaching by Coulomb screening and by the Pauli exclusion principle. The groundstate heavy-hole exciton, which experiences both effects, is unbound at hole densities in the range (6 to 11) x 10(15) m(-2). In contrast, the groundstate light-hole and first excited heavy-hole excitons: which only experience Coulomb screening, still have a finite binding energy at these densities. We found that the excitons of excited subbands are far less efficiently screened than those of the light-hole groundstate, due to the lesser overlap of the screening groundstate heavy holes with the excited subbands than with the groundstate light holes.

  • 10.
    Lloyd Spetz, Anita
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Baranzahi, Amir
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Tobias, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    High temperature sensors based on metal-insulator-silicon carbide devices1997In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 162, no 1, 493-511 p.Article in journal (Refereed)
    Abstract [en]

    High temperature gas sensors based on catalytic metal-insulator-silicon carbide (MISiC) devices are developed both as capacitors and Schottky diodes. A maximum operation temperature of 1000 degrees C is obtained for capacitors based on 4H-SiC, and all sensors work routinely for several weeks at 600 degrees C. Reducing gases like hydrocarbons and hydrogen lower the flat band voltage of the capacitor and the barrier height of the diode. The time constants for the gas response are in the order of milliseconds and because of this good performance the sensors are tested for combustion engine control. For temperatures around 600 degrees C total combustion occurs on the sensor surface and the signal is high for fuel in excess and low for air in excess. At temperatures around 400 degrees C the response is more linear. The high temperature operation causes interdiffusion of the metal and insulator layers in these devices; and this interdiffusion has been studied. At sufficiently high temperatures the inversion capacitance shows different levels for hydrogen free and hydrogen containing ambients, which is suggested to be due to a reversible hydrogen annealing effect at the insulator-silicon carbide interface.

  • 11.
    Lloyd-Spets, Anita
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Unéus, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Svenningstorp, H
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Tobias, P
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Ekedahl, Lars-Gunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Larsson, O
    Goras, A
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Savage, S
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Harris, C
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Martensson, P
    Wigren, R
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Salomonsson, P
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Haggendahl, B
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Ljung, P
    Mattsson, M
    Linkoping Univ, S SENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Medel AB, SE-66222 Amal, Sweden ABREO AB, SE-16440 Kista, Sweden Appl Sensor, SE-58330 Linkoping, Sweden Volvo TU, SE-41288 Gothenburg, Sweden Vattenfall Utveckling, SE-81426 Alvkarleby, Sweden.
    Lundström, Ingemar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    SiC based field effect gas sensors for industrial applications2001In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 185, no 1, 15-25 p.Article in journal (Refereed)
    Abstract [en]

    The development and field-testing of high-temperature sensors based on silicon carbide devices have shown promising results in several application areas. Silicon carbide based field-effect sensors can be operated over a large temperature range, 100-600 degreesC, and since silicon carbide is a chemically very inert material these sensors can be used in environments like exhaust gases and flue gases from boilers. The sensors respond to reducing gases like hydrogen, hydrocarbons and carbon monoxide. The use of different temperatures, different catalytic metals and different structures of the gate metal gives selectivity to different gases and arrays of sensors can be used to identify and monitor several components in gas mixtures. MOSFET sensors based on SIC combine the advantage of simple circuitry with a thicker insulator, which increases the long term stability of the devices. In this paper we describe silicon carbide MOSFET sensors and their performance and give: examples of industrial applications such as monitoring of car exhausts and flue gases. Chemometric methods have been used for the evaluation of the data.

  • 12.
    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.

  • 13.
    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.

  • 14.
    Monemar, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Paskov, Plamen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Haratizadeh, H.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kamiyama, S.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Iwaya, M.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Amano, H.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Akasaki, I.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Photoluminescence of InGaN/GaN and AlGaN/GaN multiple quantum well structures: Role of depletion fields and polarization fields2003In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 195, no 3, 523-527 p.Article in journal (Refereed)
    Abstract [en]

    We report on low temperature photoluminescence (PL) in InxGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si doped barriers of In0.01Ga0.99N. The MQW was placed either in the near surface depletion field or at the n-side depletion field of a pn-junction. At low temperatures the PL and electroluminescence (EL) spectra are quite different at no, low, or reverse bias, the PL appearing at higher energy. At high forward bias a spectral component at the EL position appears in PL. This proves a strong influence of the depletion field on the optical spectra. Preliminary results are also reported for Al0.07Ga0.93N/GaN structures, with near surface MQWs with 5 QWs, both Si-doped and nominally undoped. These structures show clear spectral features related to nonequivalent QWs in a graded depletion field.

  • 15.
    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, 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.
    Kamiyama, 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.
    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.
    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.
    Influence of depletion fields on photoluminescence of n-doped InGaN/GaN multiple quantum well structures2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 192, no 1, 21-26 p.Article in journal (Refereed)
    Abstract [en]

    We report on a detailed study of low temperature photoluminescence (PL) in InxGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si-doped barriers of In0.01Ga0.99N. The entire MQW structure was grown at 800 degreesC. One sample with 3 QWs of width 3.5 nm and barriers of width 10.5 nm had the MQW in the depletion region of the outer surface. Two PL peaks were observed, one QW exciton from the OW closest to the GaN buffer, one lower energy peak related to a 2DEG at the interface to the GaN buffer layer. In a second similar sample, 5 QWs of width 3 nm and with 6 nm highly Si-doped In0.01Ga0.99N barriers the MQW was placed in the n-side depletion region of a pn-junction, i.e. a complete LED structure with semitransparent top metallisation. Two PL peaks are observed also in this case, of similar origin as described above. With forward bias, this structure shows lower-energy PL emission, indicating the gradual activation of the other QWs closer to the pn-junction. At high forward bias the low-energy part of the PL spectrum becomes similar to the electroluminescence (EL) spectrum.

  • 16.
    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.

  • 17.
    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.

  • 18.
    Paskova, Tanja
    et al.
    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 .
    Darakchieva, Vanya
    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.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Defect reduction in HVPE growth of GaN and related optical spectra2001In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 183, no 1, 197-203 p.Article in journal (Refereed)
    Abstract [en]

    GaN technology is still based on highly mismatched heteroepitaxial growth on foreign substrates, and therefore needs to overcome a high defect density and a high level of stress in the epitaxial layers. Various attempts have been made to reduce the defects and stress in thick GaN layers. We here report a reduction of the defect density in thick GaN layers grown by hydride vapour phase epitaxy, using regrowth on free-standing GaN films, as well as introducing an AlN buffer and AlN interlayer in the growth sequence. Special focus is put on the optical properties of the material.

  • 19.
    Paskova, Tanja
    et al.
    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 .
    Goldys, EM
    Linkoping Univ, S-58183 Linkoping, Sweden Macquarie Univ, Sydney, NSW 2109, Australia Chalmers Univ Technol, S-41296 Gothenburg, Sweden Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland Univ Sofia, Fac Phys, BU-1126 Sofia, Bulgaria HMA, Dept Elect, S-16440 Kista, Sweden.
    Darakchieva, Vanya
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Sodervall, U
    Linkoping Univ, S-58183 Linkoping, Sweden Macquarie Univ, Sydney, NSW 2109, Australia Chalmers Univ Technol, S-41296 Gothenburg, Sweden Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland Univ Sofia, Fac Phys, BU-1126 Sofia, Bulgaria HMA, Dept Elect, S-16440 Kista, Sweden.
    Godlewski, M
    Linkoping Univ, S-58183 Linkoping, Sweden Macquarie Univ, Sydney, NSW 2109, Australia Chalmers Univ Technol, S-41296 Gothenburg, Sweden Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland Univ Sofia, Fac Phys, BU-1126 Sofia, Bulgaria HMA, Dept Elect, S-16440 Kista, Sweden.
    Zielinski, M
    Linkoping Univ, S-58183 Linkoping, Sweden Macquarie Univ, Sydney, NSW 2109, Australia Chalmers Univ Technol, S-41296 Gothenburg, Sweden Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland Univ Sofia, Fac Phys, BU-1126 Sofia, Bulgaria HMA, Dept Elect, S-16440 Kista, Sweden.
    Valcheva, E
    Linkoping Univ, S-58183 Linkoping, Sweden Macquarie Univ, Sydney, NSW 2109, Australia Chalmers Univ Technol, S-41296 Gothenburg, Sweden Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland Univ Sofia, Fac Phys, BU-1126 Sofia, Bulgaria HMA, Dept Elect, S-16440 Kista, Sweden.
    Carlstrom, CF
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Mass transport growth and properties of hydride vapour phase epitaxy GaN2001In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 188, no 1, 447-451 p.Article in journal (Refereed)
    Abstract [en]

    We report a comparative study of the optical and structural properties of mass-transport and conventionally grown GaN by hydride vapor phase epitaxy. A strong donor-acceptor pair emission is observed from the mass-transport regions with a distinctive intensity contrast between the exciton and donor-acceptor bands from mass-transport and nontransport regions. Secondary ion mass spectroscopy was employed to investigate the impurity incorporation into different regions. A moderate increase of residual impurity incorporation or redistribution was found in mass-transport regions related to different growth modes.

  • 20.
    Paskova, Tanja
    et al.
    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 .
    Valcheva, E
    Darakchieva, Vanya
    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.
    Kasic, A
    Arnaudov, B
    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 .
    Polar and nonpolar GaN grown by HVPE: Preferable substrates for nitride-based emitting devices2004In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, no 10, 2265-2270 p.Article in journal (Refereed)
    Abstract [en]

    We report on hydride vapor phase epitaxial growth of thick nonpolar GaN films on r-plane sapphire in comparison with polar GaN films on c-plane sapphire substrates with AlN buffer layers, aiming at developing of their quasi-substrate application. Both the thick films and the buffers were identified to have single crystalline structures. The microstructure of the films was studied by transmission electron microscopy. High resolution X-ray diffraction mapping and photoluminescence measurements were employed to characterize the strain present in both polar and nonpolar GaN films. In contrast to c-plane GaN, which is always characterised by isotropic in-plane properties, the a-plane GaN shows a strong in-plane anisotropy of the growth rate, morphology and strain distribution. Different defect, impurity and free carrier concentrations were observed in the polar and nonpolar material.

  • 21.
    Pozina, Galia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, JP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Bonemar, B
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Takeuchi, T
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Amano, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Akasaki, I
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Multiple peak spectra from InGaN/GaN multiple quantum wells2000In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 180, no 1, 85-89 p.Article in journal (Refereed)
    Abstract [en]

    Optical properties of In0.12Ga0.88N/GaN multiple quantum well (MQW) structures grown by metalorganic vapor phase epitaxy at 820 degrees C are reported. The transmission electron microscopy measurements show a roughness of the sample surfaces containing small pit like defects of a size 100 to 200 Angstrom with a density far exceeding the dislocation density. The photoluminescence (PL) spectra in this set of samples are dominated by strong multiple peak emissions associated both with the MQW exciton recombination and with strongly localized states of energies much lower than the QW bandgap. We suggest that the low energy PL peaks are due to (i) photocarriers localized in quantum islands closely related to the threading dislocations, and possibly associated with V-defect induced side-wall QWs, (ii) strongly localized excitons in OD quantum dots in the disordered surface region, formed by uncontrolled surface etching processes.

  • 22.
    Pozina, Galia
    et al.
    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 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kamiyama, S
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Iwaya, M
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Amano, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Akasaki, I
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 4688502, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 4688502, Japan.
    Optical study of AlGaN/GaN multiple quantum well structures grown on laterally overgrown GaN templates2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, 107-111 p.Article in journal (Refereed)
    Abstract [en]

    We report on optical studies of Al0.1Ga0.9N/GaN structures with five 30 (A) over circle thick GaN quantum wells (QWs) grown by metal organic vapor phase epitaxy using the lateral overgrowth technique. Overgrown regions demonstrate better structural and optical properties. The low temperature photoluminescence (PL) is dominated by the multiple quantum well (MQW) emission at 3.53 eV with the linewidth of similar to50 meV. The PL decay time for this line was measured to be similar to600 ps. Comparison with an AlGaN/GaN MQW light-emitting diode (LED) structure is done. The LED structure was grown with a p-type doped AlGaN top layer and a p-GaN contact layer. The PL spectrum of the LED structure shows besides the donor-acceptor pair recombination from the top layer an additional 60 meV wide line at 3.64 eV. The presence of two MQW peaks may be related to the potential gradient present across the MOW structure.

  • 23.
    Pozina, Galia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Edwards, NV
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden N Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA.
    Bergman, JP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden N Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bremser, MD
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden N Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA.
    Davis, RF
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden N Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA.
    Time-resolved photoluminescence in strained GaN layers2001In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 183, no 1, 151-155 p.Article in journal (Refereed)
    Abstract [en]

    A set of GaN epilayers grown by metalorganic chemical vapor deposition on 6H-SiC substrates was studied by time-resolved photoluminescence (PL) spectroscopy. The PL spectra are dominated by the free A exciton (FEA) and by the neutral-donor-bound exciton (D0X) transitions. The position of FEA indicates that the GaN layers are under tension. We observe that the recombination lifetime for the FEA is about 40-50 ps in all the layers, whereas the recombination time for the D0X varies for different samples. We found that the recombination lifetimes for D0X have a clear dependence on the position of FEA, i.e. the recombination lifetime increases with decreasing strain in the layers. The results can be explained in terms of the character of the hole states involved in the donor-bound exciton recombination.

  • 24.
    Shubina, Tatiana
    et al.
    Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Jmerik, V.N.
    Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Tkachman, M.G.
    Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Vekshin, V.A.
    Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Toropov, A.A.
    Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Ivanov, S.V.
    Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Kop'ev, P.S.
    Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Karlsson, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Optical properties of GaN/AlGaN quantum wells with inversion domains2003In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 195, no 3, 537-542 p.Article in journal (Refereed)
    Abstract [en]

    Two-band photoluminescence (PL) and respective absorption and reflection features are observed in GaN/AlGaN MBE-grown quantum well (QW) structures of dominant N polarity with inversion domains (IDs). The PL bands are related to transitions in the regions of different polarity, characterized by different strain and electric fields. A micro-PL study reveals sharp and narrow (1.5-2.5 meV) PL lines placed between the bands, which are tentatively attributed to recombination at localization sites associated with intersections of the QWs with the domains. Additionally, we demonstrate that the ID formation decreases the overall strength of the intrinsic electric fields in the QW structures.

  • 25.
    Shubina, Tatiana
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Toropov, AA
    AF Ioffe Phys Tech Inst, St Petersburg 194021, Russia Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
    Ivanov, SV
    AF Ioffe Phys Tech Inst, St Petersburg 194021, Russia Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
    Bergman, JP
    AF Ioffe Phys Tech Inst, St Petersburg 194021, Russia 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.
    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 .
    Peculiarities of exciton-polaritons in GaN at different polarizations studied by mu-photoluminescence spectroscopy2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, no 1, 205-211 p.Article in journal (Refereed)
    Abstract [en]

    We report on polariton properties in high quality thick GaN grown by hydride vapor phase epitaxy on c-sapphire. A strong fine is observed in the vicinity of the A exciton in T-polarization (k perpendicular to c, E parallel to the c-axis) by micro-photoluminescence (mu-PL). Comparison of the mu-PL and mu-reflectance spectra confirms the internal origin of the polariton emission. In the samples with low density of residual donors the enhancement of the a-polarized component is induced mostly by interbranch scattering which occurs, possibly., due to the complex structure of the exciton-polariton branches at k perpendicular to c. The Gamma(1)-Gamma(5) exciton splitting in the C band is determined by the mu-reflectance as similar to1 meV.

  • 26. Valcheva, E
    et al.
    Paskova, Tanja
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Persson, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nanopipes in thick GaN films grown at high growth rate2002In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 194, no 2, 532-535 p.Article in journal (Refereed)
    Abstract [en]

    In this work we illustrate and describe long propagating nanopipes in thick HVPE-GaN layers analysed by means of transmission electron microscopy. They are observed to behave like screw component threading dislocations, terminating surface steps by hexagonal pits, and thus leading to the possibility of spiral growth. The formation of a nanopipe is observed by trapping of a screw dislocation at a pinhole that opens in an empty core. The mechanism of formation of nanopipes is likely to be connected to the growth kinetics of screw dislocations in the early stages of growth of highly strained material.

  • 27.
    Zangooie, S
    et al.
    Linkoping Univ, Lab Appl Opt, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden Univ Nebraska, Ctr Microelect & Opt Mat Res, Lincoln, NE 68588 USA Univ Nebraska, Dept Elect Engn, Lincoln, NE 68588 USA.
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Porous anodic 4H-SiC: Thickness dependent anisotropy in pore propagation and ellipsometric characterization2000In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 182, no 1, 213-219 p.Article in journal (Refereed)
    Abstract [en]

    Pores in porous 4H-SiC propagate first nearly parallel with the sample surface and gradually change direction tc,wards the direction of the c-axis. A disordered region at the interface between crystalline SiC and the pores is encountered ed, which significantly influences the optical response of the material. Thickness and porosity of porous SIC as obtained using variable angle of incidence spectroscopic ellipsometry show good agreement with electron microscopy observations.

1 - 27 of 27
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