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  • 51. 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.

  • 52.
    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.

  • 53. 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, p. 285-286Article in journal (Refereed)
  • 54. 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).

  • 55.
    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, p. 563-571Article 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.

  • 56.
    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, p. 2590-2592Article 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.

  • 57.
    Arshad, Sana
    et al.
    NED University of Engn and Technology, Pakistan.
    Ramzan, Rashad
    United Arab Emirates University, U Arab Emirates.
    Wahab, Qamar-ul
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    50-830 MHz noise and distortion canceling CMOS low noise amplifier2018In: Integration, ISSN 0167-9260, E-ISSN 1872-7522, Vol. 60, p. 63-73Article in journal (Refereed)
    Abstract [en]

    In this paper, a modified resistive shunt feedback topology is proposed that performs noise cancelation and serves as an opposite polarity non-linearity generator to cancel the distortion produced by the main stage. The proposed topology has a bandwidth similar to a resistive shunt feedback LNA, but with a superior noise figure (NF) and linearity. The proposed wideband LNA is fabricated in 130 nm CMOS technology and occupies an area of 0.5 mm(2). Measured results depict 3-dB bandwidth from 50 to 830 MHz. The measured gain and NF at 420 MHz are 17 dB and 2.2 dB, respectively. The high value of the 1/f noise is one of the key problems in low frequency CMOS designs. The proposed topology also addresses this challenge and a low NF is attained at low frequencies. Measured 811 and S22 are better than -8.9 dB and -8.5 dB, respectively within the 0.05-1 GHz band. The 1-dB compression point is -11.5 dBm at 700 MHz, while the IIP3 is -6.3 dBm. The forward core consumes 14 mW from a 1.8 V supply. This LNA is suitable for VHF and UHF SDR communication receivers.

  • 58.
    Arslan, Engin
    et al.
    Bilkent University, Turkey .
    Cakmakyapan, Semih
    Bilkent University, Turkey .
    Kazar, Ozgur
    Bilkent University, Turkey .
    Butun, Serkan
    Bilkent University, Turkey .
    Bora Lisesivdin, Sefer
    Gazi University, Turkey .
    Cinel, Neval A.
    Bilkent University, Turkey .
    Ertas, Gulay
    Bilkent University, Turkey .
    Ardali, Sukru
    Anadolu University, Turkey .
    Tiras, Engin
    Anadolu University, Turkey .
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ozbay, Ekmel
    Bilkent University, Turkey .
    SiC Substrate Effects on Electron Transport in the Epitaxial Graphene Layer2014In: ELECTRONIC MATERIALS LETTERS, ISSN 1738-8090, Vol. 10, no 2, p. 387-391Article in journal (Refereed)
    Abstract [en]

    Hall effect measurements on epitaxial graphene (EG) on SiC substrate have been carried out as a function of temperature. The mobility and concentration of electrons within the two-dimensional electron gas (2DEG) at the EG layers and within the underlying SiC substrate are readily separated and characterized by the simple parallel conduction extraction method (SPCEM). Two electron carriers are identified in the EG/SiC sample: one high-mobility carrier (3493 cm(2)/Vs at 300 K) and one low-mobility carrier (1115 cm(2)/Vs at 300 K). The high mobility carrier can be assigned to the graphene layers. The second carrier has been assigned to the SiC substrate.

  • 59.
    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)
  • 60.
    Asada, Satoshi
    et al.
    Department of Electronic Science and Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, Japan.
    Kimoto, Tsunenobu
    Department of Electronic Science and Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, Japan.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Calibration on wide-ranging aluminum doping concentrations by photoluminescence in high-quality uncompensated p-type 4H-SiC2017In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, no 7, article id 072101Article in journal (Refereed)
    Abstract [en]

    Previous work has shown that the concentration of shallow dopants in a semiconductor can be estimated from the photoluminescence (PL) spectrum by comparing the intensity of the bound-to-the- dopant exciton emission to that of the free exciton. In this work, we study the low-temperature PL of high-quality uncompensated Al-doped p-type 4H-SiC and propose algorithms for determining the Al-doping concentration using the ratio of the Al-bound to free-exciton emission. We use three different cryogenic temperatures (2, 41, and 79 K) in order to cover the Al-doping range from mid 10(14) cm(-3) up to 10(18) cm(-3). The Al-bound exciton no-phonon lines and the strongest free-exciton replica are used as a measure of the bound-and free-exciton emissions at a given temperature, and clear linear relationships are obtained between their ratio and the Al-concentration at 2, 41, and 79 K. Since nitrogen is a common unintentional donor dopant in SiC, we also discuss the criteria allowing one to determine from the PL spectra whether a sample can be considered as uncompensated or not. Thus, the low-temperature PL provides a convenient non-destructive tool for the evaluation of the Al concentration in 4H-SiC, which probes the concentration locally and, therefore, can also be used for mapping the doping homogeneity. Published by AIP Publishing.

  • 61. Asghar, M.
    et al.
    Hussain, I.
    Noor, N.
    Iqbal, F.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bhatti, A.
    Properties of dominant electron trap center in n-type SiC epilayers by means of deep level transient spectroscopy2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 7Article in journal (Refereed)
    Abstract [en]

    Characterization of dominant electron trap in as-grown SiC epilayers has been carried out using deep level transient spectroscopy. Two electron traps E1 and Z1 at Ec-0.21 and Ec-0.61 are observed, respectively, Z1 being the dominant level. Line shape fitting, capture cross section, and insensitivity with doping concentration have revealed interesting features of Z1 center. Spatial distribution discloses that the level is generated in the vicinity of epilayers/substrate interface and the rest of the overgrown layers is defect-free. Owing to the Si-rich growth conditions, the depth profile of Z1 relates it to carbon vacancy. The alpha particle irradiation transforms Z1 level into Z 1/Z2 center involving silicon and carbon vacancies. Isochronal annealing study further strengthens the proposed origin of the debated level. © 2007 American Institute of Physics.

  • 62.
    Asghar, M.
    et al.
    Islamia University of Bahawalpur, Pakistan .
    Iqbal, F.
    Islamia University of Bahawalpur, Pakistan .
    Faraz, Sadia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy2012Conference paper (Refereed)
    Abstract [en]

    In this study deep level transient spectroscopy has been performed on boron-nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N-A-N-D)similar to 3 x 10(17) cm(-3). We observed a hole H-1 majority carrier and an electron E-1 minority carrier traps in the device having activation energies E-nu + 0.24 eV, E-c -0.41 eV, respectively. The capture cross-section and trap concentration of H-1 and E-1 levels were found to be (5 x 10(-19) cm(2), 2 x 10(15) cm(-3)) and (1.6 x 10(-16) cm(2), 3 x 10(15) cm(-3)), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H-1 defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E-1 defect to a nitrogen donor.

  • 63.
    Asghar, M.
    et al.
    Islamia University of Bahawalpur, Pakistan .
    Iqbal, F.
    Islamia University of Bahawalpur, Pakistan .
    Faraz, Sadia Municha
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Study of deep level defects in doped and semi-insulating n-6H-SiC epilayers grown by sublimation method2012Conference paper (Refereed)
    Abstract [en]

    Deep level transient spectroscopy (DLTS) is employed to study deep level defects in n-6H-SiC (silicon carbide) epilayers grown by the sublimation method. To study the deep level defects in n-6H-SiC, we used as-grown, nitrogen doped and nitrogen-boron co-doped samples represented as ELS-1, ELS-11 and ELS-131 having net (N-D-N-A) similar to 2.0 x 10(12) cm(-3), 2 x 10(16) cm(-3) and 9 x 10(15) cm(3), respectively. The DLTS measurements performed on ELS-1 and ELS-11 samples revealed three electron trap defects (A, B and C) having activation energies E-c - 0.39 eV, E-c - 0.67 eV and E-c - 0.91 eV, respectively. While DLTS spectra due to sample ELS-131 displayed only A level. This observation indicates that levels B and C in ELS-131 are compensated by boron and/or nitrogen-boron complex. A comparison with the published data revealed A, B and C to be E-1/E-2, Z(1)/Z(2) and R levels, respectively.

  • 64.
    Ashkenov, N.
    et al.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Mbenkum, B.N.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Bundesmann, C.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Riede, V.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Lorenz, M.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Spemann, D.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Kaidashev, E.M.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany, Rostov State University, Mech./Appl. Math. Research Institute, 200/1 Stachky Avenue, Rostov-on-Don 344090, Russian Federation.
    Kasic, A.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Schubert, M.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Grundmann, M.
    Universität Leipzig, Fak. F. Phys. and Geowissenschaften, Inst. F. Experimentelle Physik II, Linnéstrasse 5, 04103 Leipzig, Germany.
    Wagner, G.
    Inst. F. Nichtklassische Chem. e.V., Universität Leipzig, Permoserstraße 15, 04318 Leipzig, Germany.
    Neumann, H.
    Inst. F. O. e.V., Permoserstrasse 15, 04303 Leipzig, Germany.
    Darakchieva, Vanya
    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 .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Infrared dielectric functions and phonon modes of high-quality ZnO films2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 1, p. 126-133Article in journal (Refereed)
    Abstract [en]

    A study was performed on the phonon modes and infrared dielectric functions of high-quality ZnO thin films. The pulsed laser deposition technique was used to deposit the ZnO films on c-plane sapphire substrates and were investigated by high-resolution transmission electron microscopy, high-resolution x-ray diffraction and Rutherford backscattering experiments. The accurate long-wavelength dielectric constant limits of the films were also obtained and were compared with near-band-gap index-of-refraction data upon the Lyddane-Sachs-Teller relation for both film and bulk samples. It was found that the phonon modes of the film were highly consistent with those of the bulk sample.

  • 65.
    Ashraf, H.
    et al.
    Radboud University Nijmegen.
    Imran Arshad, M.
    Islamia University Bahawalpur.
    Muniza Faraz, Sadia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hageman, P. R.
    Radboud University Nijmegen.
    Asghar, M.
    Islamia University Bahawalpur.
    Study of electric field enhanced emission rates of an electron trap in n-type GaN grown by hydride vapor phase epitaxy2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed)
    Abstract [en]

    Electric field-enhanced emission of electrons from a deep level defect in GaN grown by hydride vapor phase epitaxy has been studied. Using the field dependent mode of conventional deep level transient spectroscopy (DLTS), several frequency scans were performed keeping applied electric field (12.8-31.4 MV/m) and sample temperature (300-360 K) constant. Arrhenius plots of the resultant data yielded an activation energy of the electron trap E ranging from E-c -0.48 +/- 0.02 eV to E-c-0.35 +/- 0.02 eV, respectively. The extrapolation of the as-measured field dependent data (activation energy) revealed the zero-field emission energy (pure thermal activation energy) of the trap to be 0.55 +/- 0.02 eV. Various theoretical models were applied to justify the field-enhanced emission of the carriers from the trap. Eventually it was found that the Poole-Frenkel model associated with a square well potential of radius r=4.8 nm was consistent with the experimental data, and, as a result, the trap is attributed to a charged impurity. Earlier, qualitative measurements like current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed, and screening parameters of the device were extracted to ascertain the reliability of DLTS data.

  • 66. Atanassov, A
    et al.
    Baleva, M
    Darakchieva, Vanya
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Goranova, E
    Grazing incident asymmetric X-ray diffraction of beta-FeSi2 layers, produced by ion beam synthesis2004In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 76, no 02-Mar, p. 277-280Article in journal (Refereed)
    Abstract [en]

    The crystal structure of beta-FeSi2 phase, prepared by ion beam synthesis (IBS) method, followed by rapid thermal annealing (RTA) is investigated by grazing incident asymmetric X-ray diffraction (GIAXRD). The X-ray spectra, obtained at different grazing angles, indicated that the beta-FeSi2 phase is formed in the whole implantation range. From the comparison of the reflections intensities ratios, it is found that in the metal-deficient regions, where the beta-FeSi2 phase is present in the form of precipitates, the crystallites orientation is influenced by the one of the silicon substrates, while the orientation in the metal-rich region is different and depends on the annealing temperature. (C) 2004 Elsevier Ltd. All rights reserved.

  • 67. Atlasov, K.A.
    et al.
    Felici, M.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Gallo, P.
    Rudra, A.
    Dwir, B.
    Kapon, E.
    Tracking 1D photonic band formation in finite-size photonic crystal waveguides: disorder and localization effects2008In: 29th International Conference on the Physics of Semiconductors ICPS,2008, 2008Conference paper (Other academic)
  • 68. Atlasov, K.A.
    et al.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Deichsel, E.
    Dwir, B.
    Rudra, A.
    Kapon, E.
    Quantum Wire Lasers Utilizing Novel Optical Cavities2005In: EPFL Journee de la recherché,2005, 2005Conference paper (Other academic)
  • 69.
    Atlasov, K.A.
    et al.
    Lab. of Phys. of Nanostruct., Ecole Polytech. Fed. de Lausanne, Lausanne.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Lab. of Phys. of Nanostruct., Ecole Polytech. Fed. de Lausanne, Lausanne.
    Gallo, P.
    Lab. of Phys. of Nanostruct., Ecole Polytech. Fed. de Lausanne, Lausanne.
    Rudra, A.
    Lab. of Phys. of Nanostruct., Ecole Polytech. Fed. de Lausanne, Lausanne.
    Dwir, B.
    Lab. of Phys. of Nanostruct., Ecole Polytech. Fed. de Lausanne, Lausanne.
    Kapon, E.
    Lab. of Phys. of Nanostruct., Ecole Polytech. Fed. de Lausanne, Lausanne.
    Observation of Stimulated Emission and Lasing in Quantum-wire Photonic-crystal Nanocavities2009In: IEEE/LEOS Winter Topical Meeting Series on Nanophotonics,2009, 2009Conference paper (Other academic)
  • 70. Atlasov, K.A.
    et al.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Gallo, P.
    Rudra, A.
    Dwir, B.
    Kapon, E.
    Quantum-Wire Lasers Based on Photonic-Crystal Nanocavities2008In: 17th International Laser Physics Workshop,2008, 2008Conference paper (Other academic)
  • 71. Atlasov, K.A.
    et al.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kapon, E.
    Design of High-Q Membrane Photonic Crystal Defect Cavity for Integration with Semiconductor Quantum Wires2006In: 9th International conference on near-field optics, nanophotonics and related techniques NFO 9,2006, 2006Conference paper (Other academic)
  • 72. Atlasov, K.A.
    et al.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rudra, A.
    Dwir, B.
    Kapon, E.
    Observation of Wavelength- and Loss-Splitting of Supermodes in Coupled Photonic-Crystal Microcavities2008In: Conference on Lasers and Electro-Optics CLEO,2008, 2008Conference paper (Other academic)
  • 73. Atlasov, K.A.
    et al.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rudra, A.
    Dwir, B.
    Kapon, E.
    Wavelength and loss splitting in directly coupled photonic-crystal defect microcavities2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 20, p. 16255-16264Article in journal (Refereed)
    Abstract [en]

    Coupling between photonic-crystal defect microcavities is observed to result in a splitting not only of the mode wavelength but also of the modal loss. It is discussed that the characteristics of the loss splitting may have an important impact on the optical energy transfer between the coupled resonators. The loss splitting - given by the imaginary part of the coupling strength - is found to arise from the difference in diffractive outof-plane radiation losses of the symmetric and the antisymmetric modes of the coupled system. An approach to control the splitting via coupling barrier engineering is presented. © 2008 Optical Society of America.

  • 74. Atlasov, K.A.
    et al.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rudra, A.
    Kapon, E.
    1D Exciton-Photon Confinements in V-groove Quantum Wires Embedded into Photonic-Crystal Membrane Microcavities2007In: Second International Conference on One-dimensional Nanomaterials ICON 2007,2007, 2007Conference paper (Other academic)
  • 75. Atlasov, K.A.
    et al.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rudra, A.
    Kapon, E.
    Integration of a Single V-groove Quantum Wire into 2D Photonic Crystal Membrane Microcavity2006In: 6th International Conference on Physics of Light-Matter Coupling in Nanostructures,2006, 2006Conference paper (Other academic)
  • 76.
    Atlasow, Kirill A.
    et al.
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Calic, Milan
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Karlsson, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology. Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Gallo, Pascal
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Rudra, Alok
    n/Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Dwir, Benjamin
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Kapon, Eli
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Photonic-crystal microcavity laser with site-controlled quantum-wire active medium2009In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 20, p. 18178-18183Article in journal (Refereed)
    Abstract [en]

    Site-controlled quantum-wire photonic-crystal microcavity laser is experimentally demonstrated using optical pumping. The single-mode lasing and threshold are established based on the transient laser response, linewidth narrowing, and the details of the non-linear power input-output charateristics. Average-power threshold as low as ~240 nW (absorbed power) and spontaneous emission coupling coefficient β~0.3 are derived.

  • 77.
    Ayedh, Hussein M.
    et al.
    University of Oslo, Department of Physics, Center for Materials Science and Nanotechnology, N-0316 Oslo, NORWAY .
    Baathen, Marianne E.
    University of Oslo, Department of Physics, Center for Materials Science and Nanotechnology, N-0316 Oslo, NORWAY .
    Galeckas, Augustinas
    University of Oslo, Department of Physics, Center for Materials Science and Nanotechnology, N-0316 Oslo, NORWAY .
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Nipoti, Roberta
    CNR-IMM of Bologna, I-40129 Bologna, ITALY.
    Hallen, Anders
    Royal Institute of Technology, KTH, School of Information and Communication Technology, SE-164 40 Kista-Stockholm, SWEDEN.
    Svensson, Bengt G
    University of Oslo, Department of Physics, Center for Materials Science and Nanotechnology, N-0316 Oslo, NORWAY.
    (Invited) Controlling the Carbon Vacancy in 4H-SiC by Thermal Processing2018In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, ECS Transactions, Vol. 86, no 12, p. 91-97Article in journal (Refereed)
    Abstract [en]

    The carbon vacancy (VC) is perhaps the most prominent point defect in silicon carbide (SiC) and it is an efficient charge carrier lifetime killer in high-purity epitaxial layers of 4H-SiC. The VC concentration needs to be controlled and minimized for optimum materials and device performance, and an approach based on post-growth thermal processing under C-rich ambient conditions is presented. It utilizes thermodynamic equilibration and after heat treatment at 1500 °C for 1 h, the VC concentration is shown to be reduced by a factor ~25 relative to that in as-grown state-of-the-art epi-layers. Concurrently, a considerable enhancement of the carrier lifetime occurs throughout the whole of >40 µm thick epi-layers.

  • 78.
    Azam, Sher
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Microwave Power Devices and Amplifiers for Radars and Communication Systems2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    SiC MESFETs and GaN HEMTs posses an enormous potential in power amplifiers at microwave frequencies due to their wide bandgap features of high electric field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. Similarly Si-LDMOS being low cost and lonely silicon based RF power transistor has great contributions especially in the communication sector.

    The focus of this thesis work is both device study and their application in different classes of power amplifiers. In the first part of our research work, we studied the performance of transistors in device simulation using physical transistor structure in Technology Computer Aided Design (TCAD). A comparison between the physical simulations and measured device characteristics has been carried out.  We optimized GaN HEMT, Si-LDMOS and enhanced version of our previously fabricated and tested SiC MESFET transistor for enhanced RF and DC characteristics. For large signal AC performance we further extended the computational load pull (CLP) simulation technique to study the switching response of the power transistors. The beauty of our techniques is that, we need no lumped or distributive matching networks to study active device behavior in almost all major classes of power amplifiers. Using these techniques, we studied class A, AB, pulse input class-C and class-F switching response of SiC MESFET. We obtained maximum PAE of 78.3 % with power density of 2.5 W/mm for class C and 84 % for class F power amplifier at 500 MHz. The Si-LDMOS has a vital role and is a strong competitor to wideband gap semiconductor technology in communication sector. We also studied Si-LDMOS (transistor structure provided by Infineon Technologies at Kista, Stockholm) for improved DC and RF performance. The interface charges between the oxide and RESURF region are used not only to improve DC drain current and RF power, gain & efficiency but also enhance its operating frequency up to 4 GHz.

    In the second part of our research work, six single stage (using single transistor) power amplifiers have been designed, fabricated and characterized in three phases for applications in communications, Phased Array Radars and EW systems. In the first phase, two class AB power amplifiers are designed and fabricated. The first PA (26 W) is designed and fabricated at 200-500 MHz using SiC MESFET. Typical results for this PA at 60 V drain bias at 500 MHz are, 24.9 dB of power gain, 44.15 dBm output power (26 W) and 66 % PAE. The second PA is designed at 30-100 MHz using SiC MESFET. At 60 V drain bias Pmax is 46.7 dBm (~47 W) with a power gain of 21 dB.

    In the second phase, for performance comparison, three broadband class AB power amplifiers are designed and fabricated at 0.7-1.8 GHz using SiC MESFET and two different GaN HEMT technologies (GaN HEMT on SiC and GaN HEMT on Silicon substrate). The measured maximum output power for the SiC MESFET amplifier at a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The results for GaN HEMT on SiC amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The maximum output power for GaN HEMT on Si amplifier is 42.5 dBm (~18 W) with a maximum PAE of 39 % and a gain of 19.5 dB.

    In the third phase, a high power single stage class E power amplifier is implemented with lumped elements at 0.89-1.02 GHz using Silicon GaN HEMT as an active device. The maximum drain efficiency (DE) and PAE of 67 and 65 % respectively is obtained with a maximum output power of 42.2 dBm (~ 17 W) and a maximum power gain of 15 dB.

    List of papers
    1. Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
    Open this publication in new window or tab >>Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
    2008 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 52, no 5, p. 740-744Article in journal (Refereed) Published
    Abstract [en]

    The switching behavior of a previously fabricated and tested SiC transistor is studied in Class-C amplifier in TCAD simulation. The transistor is simulated for pulse input signals in Class-C power amplifier. The simulated gain (dB), power density (W/mm) and power added efficiency (PAE%) at 500 MHz, 1, 2 and 3 GHz was studied using computational TCAD load pull simulation technique. A Maximum PAE of 77.8% at 500 MHz with 45.4 dB power gain and power density of 2.43 W/mm is achieved. This technique allows the prediction of switching response of the device for switching amplifier Classes (Class-C–F) before undertaking an expensive and time consuming device fabrication. The beauty of this technique is that, we need no matching and other lumped element networks for studying the large signal behavior of RF and microwave transistors.

    Keywords
    Pulse, Class-C, Power amplifier, New technique, Silicon carbide, MESFET
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13285 (URN)10.1016/j.sse.2007.09.022 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2017-12-13Bibliographically approved
    2. High Power, High Efficiency SiC Power Amplifier for Phased ArrayRadar and VHF Applications
    Open this publication in new window or tab >>High Power, High Efficiency SiC Power Amplifier for Phased ArrayRadar and VHF Applications
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Wide band gap semiconductor (SiC & GaN) based power amplifiers offer severalsystem critical advantages such as less current leakage, better stability at high temperatureand easier impedance matching. This paper describes the design and fabrication of a singlestageclass-AB power amplifier for 30 to 100 MHz using SiC Schottky gate MetalSemiconductor Field Effect Transistor (MESFET). The maximum output power achieved is46.2 dBm (~42 W) at 50 V DC supply voltage at the drain. The maximum power gain is 21dB and a maximum PAE of 62 %. The amplifier performance was also checked at a higherdrain bias of 60 V at 50 MHz. At this bias voltage the maximum output power was 46.7dBm (~47 W) with a power gain of 21 dB and a maximum PAE of 42.7 %. An averageOIP3 of 54 dBm have been achieved for this amplifier.

    Keywords
    Power Amplifier, Phased Array Radar, VHF, Silicon Carbide and MESFET.
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-20862 (URN)
    Available from: 2009-09-24 Created: 2009-09-24 Last updated: 2018-10-08Bibliographically approved
    3. Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
    Open this publication in new window or tab >>Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
    2006 (English)In: Microwave Conference, 2006. APMC 2006. Asia-Pacific December 12-15, 2006, p. 441-444Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper describes a single-stage 26 W negative feedback power amplifier, covering the frequency range 200-500 MHz using a 6 mm gate width SiC lateral epitaxy MESFET. Typical results at 50 V drain bias for the whole band are, around 22 dB power gain, around 43 dBm output power, minimum power added efficiency at P1 dB is 47% at 200 MHz and maximum 60% at 500 MHz and the IMD3 level at 10 dB back-off from P1 dB is below -45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66% PAE.

    Keywords
    Schottky gate field effect transistors, feedback, microwave power amplifiers, silicon compounds, SiC, frequency 200 MHz to 500 MHz, lateral epitaxy MESFET, negative feedback, power 26 W, power amplifier, size 6 mm, voltage 50 V
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13283 (URN)10.1109/APMC.2006.4429458 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2009-09-24Bibliographically approved
    4. Broadband Power Amplifier performance of SiC MESFET and CostEffective SiGaN HEMT
    Open this publication in new window or tab >>Broadband Power Amplifier performance of SiC MESFET and CostEffective SiGaN HEMT
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    This paper describes the broadband power amplifier performance of two differentwide band gap technology transistors at 0.7 to 1.8 GHz using cost effective NitronexGaN HEMT on Silicon (Si) and Cree Silicon Carbide MESFET. The measured resultsfor GaN amplifier are; maximum output power at Vd = 28 V is 42.5 dBm (~18 W), amaximum PAE of 39 % and a maximum gain of 19.5 dB is obtained. The measuredmaximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W),with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd = 66 V at700 MHz for SiC MESFET amplifier the Pmax was 42.2 dBm (~16.6 W) with a PAE of34.4 %.

    Keywords
    Broadband, Power Amplifier, GaN HEMT, Silicon Carbide (SiC), MESFET
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-20863 (URN)
    Available from: 2009-09-24 Created: 2009-09-24 Last updated: 2010-01-14Bibliographically approved
    5. Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies
    Open this publication in new window or tab >>Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies
    2008 (English)In: IEEE European Microwave Week, October 10-15, Amsterdam, The Netherlands, 2008, p. 444-447Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper describes the design, fabrication and measurement of two single-stage class-AB power amplifiers covering the frequency band from 0.7-1.8 GHz using a SiC MESFET and a GaN HEMT. The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32% and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4%. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34% and a power gain above 10 dB. The results for SiC amplifier are better than for GaN amplifier for the same 10-W transistor.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13284 (URN)10.1109/EUMC.2008.4751484 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2009-09-24Bibliographically approved
    6. High Power, Single Stage SiGaN HEMT Class EPower Amplifier at GHz Frequencies
    Open this publication in new window or tab >>High Power, Single Stage SiGaN HEMT Class EPower Amplifier at GHz Frequencies
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    A high power single stage class E power amplifier is implemented with lumped elements at 0.89-1.02GHz using Silicon GaN High Electron Mobility Transistor as an active device. The maximum drain efficiency (DE) and power added efficiency (PAE) of 67 and 65 % respectively is obtained with a maximum output power of 42.2 dBm (~ 17 W) and amaximum power gain of 15 dB. We obtained good results at all measured frequencies.

    Keywords
    Class E, PAE, Power Amplifiers, Gallium Nitride, HEMT
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-20864 (URN)
    Available from: 2009-09-24 Created: 2009-09-24 Last updated: 2019-09-05Bibliographically approved
    7. A New Load Pull TCAD Simulation Technique for Class D, E & FSwitching Characteristics of Transistors
    Open this publication in new window or tab >>A New Load Pull TCAD Simulation Technique for Class D, E & FSwitching Characteristics of Transistors
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    We have further developed a computational load pull simulation technique inTCAD. It can be used to study the Class-D, E & F switching response of the transistors. Westudied our enhanced version of previously fabricated and tested SiC transistor. Thesimulated Gain (dB), Power density (W/mm), switching loss (W/mm) and power addedefficiency (PAE %) at 500 MHz were studied using this technique. A PAE of 84 % at500MHz with 26 dB Power gain and power density of 2.75 W/mm is achieved. Thistechnique allows the prediction of switching response of the device before undertaking anexpensive and time-consuming device fabrication. The beauty of this technique is that, weneed no matching and other lumped element networks to study the large signal switchingbehavior of RF and microwave transistors.

    Keywords
    Power Amplifier, Silicon Carbide, TCAD, Switching, Technique
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-20865 (URN)
    Available from: 2009-09-24 Created: 2009-09-24 Last updated: 2010-01-14Bibliographically approved
    8. Influence of interface state charges on RF performance of LDMOS transistor
    Open this publication in new window or tab >>Influence of interface state charges on RF performance of LDMOS transistor
    Show others...
    2008 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 52, no 7, p. 1099-1105Article in journal (Refereed) Published
    Abstract [en]

    Si-LDMOS transistor is studied by TCAD simulation for improved RF performance. In LDMOS structure, a low-doped reduced surface field (RESURF) region is used to obtain high breakdown voltage, but it reduces the transistor RF performance due to high on-resistance. The interface charges between oxide and the RESURF region are studied and found to have a strong impact on the transistor performance both in DC and RF. The presence of excess interface state charges at the RESURF region results not only higher DC drain current but also improved RF performance in terms of power, gain and efficiency. The most important achievement is the enhancement of operating frequency and RF output power is obtained well above 1 W/mm up to 4 GHz.

    Place, publisher, year, edition, pages
    Elsevier, 2008
    Keywords
    Semiconductor devices; Interface state charges; Power electronics; Amplifiers; CAD simulations
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-20866 (URN)10.1016/j.sse.2008.04.001 (DOI)
    Available from: 2009-09-24 Created: 2009-09-24 Last updated: 2017-12-13Bibliographically approved
    9. Comparison of Two GaN TransistorsTechnology in Broadband Power Amplifiers
    Open this publication in new window or tab >>Comparison of Two GaN TransistorsTechnology in Broadband Power Amplifiers
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    This paper compares the performance of two different GaN technology transistors(GaN HEMT on Silicon substrate (PA1) and GaN on SiC PA2) utilized in two broadbandpower amplifiers at 0.7-1.8 GHz. The study explores the broadband power amplifierpotential of both GaN HEMT technologies for Phased Array Radar (PAR) and electronicswarfare (EW) systems. The measured maximum output power for PA1 is 42.5 dBm(~18 W) with a maximum PAE of 39 % and a gain of 19.5 dB. While the measuredmaximum output power for PA2 is 40 dBm with PAE of 35 % and a power gain slightlyabove 10 dB. We obtained high power, gain, wider band width and unconditionalstability without feedback for amplifier based on GaN HEMT technology fabricated on Sisubstrate.

    Keywords
    Broadband, Power Amplifier, GaN, HEMT and Single-Stage
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-20867 (URN)
    Available from: 2009-09-24 Created: 2009-09-24 Last updated: 2010-01-14Bibliographically approved
  • 79.
    Azam, Sher
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Wide Bandgap Semiconductor (SiC & GaN) Power Amplifiers in Different Classes2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    SiC MESFETs and GaN HEMTs have an enormous potential in high-power amplifiers at microwave frequencies due to their wide bandgap features of high electric breakdown field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. In this thesis, Class C switching response of SiC MESFET in TCAD and two different generations of broadband power amplifiers have been designed, fabricated and characterized. Input and output matching networks and shunt feedback topology based on microstrip and lumped components have been designed, to increase the bandwidth and to improve the stability. The first amplifier is a single stage 26-watt using a SiC MESFET covering the frequency from 200-500 MHz is designed and fabricated. Typical results at 50 V drain bias for the whole band are, 22 dB power gain, 43 dBm output power, minimum power added efficiency at P 1dB is 47 % at 200 MHz and maximum 60 % at 500 MHz and the IMD3 level at 10 dB back-off from P 1dB is below ‑45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66 % PAE.

    In the second phase, two power amplifiers at 0.7-1.8 GHz without feed back for SiC MESFET and with feedback for GaN HEMT are designed and fabricated (both these transistors were of 10 W). The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The SiC amplifier gives better results than for GaN amplifier for the same 10 W transistor.

    A comparison between the physical simulations and measured device characteristics has also been carried out. A novel and efficient way to extend the physical simulations to large signal high frequency domain was developed in our group, is further extended to study the class-C switching response of the devices. By the extended technique the switching losses, power density and PAE in the dynamics of the SiC MESFET transistor at four different frequencies of 500 MHz, 1, 2 and 3 GHz during large signal operation and the source of switching losses in the device structure was investigated. The results obtained at 500 MHz are, PAE of 78.3%, a power density of 2.5 W/mm with a switching loss of 0.69 W/mm. Typical results at 3 GHz are, PAE of 53.4 %, a power density of 1.7 W/mm with a switching loss of 1.52 W/mm.

    List of papers
    1. Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
    Open this publication in new window or tab >>Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
    2006 (English)In: Microwave Conference, 2006. APMC 2006. Asia-Pacific December 12-15, 2006, p. 441-444Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper describes a single-stage 26 W negative feedback power amplifier, covering the frequency range 200-500 MHz using a 6 mm gate width SiC lateral epitaxy MESFET. Typical results at 50 V drain bias for the whole band are, around 22 dB power gain, around 43 dBm output power, minimum power added efficiency at P1 dB is 47% at 200 MHz and maximum 60% at 500 MHz and the IMD3 level at 10 dB back-off from P1 dB is below -45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66% PAE.

    Keywords
    Schottky gate field effect transistors, feedback, microwave power amplifiers, silicon compounds, SiC, frequency 200 MHz to 500 MHz, lateral epitaxy MESFET, negative feedback, power 26 W, power amplifier, size 6 mm, voltage 50 V
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13283 (URN)10.1109/APMC.2006.4429458 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2009-09-24Bibliographically approved
    2. Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies
    Open this publication in new window or tab >>Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies
    2008 (English)In: IEEE European Microwave Week, October 10-15, Amsterdam, The Netherlands, 2008, p. 444-447Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper describes the design, fabrication and measurement of two single-stage class-AB power amplifiers covering the frequency band from 0.7-1.8 GHz using a SiC MESFET and a GaN HEMT. The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32% and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4%. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34% and a power gain above 10 dB. The results for SiC amplifier are better than for GaN amplifier for the same 10-W transistor.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13284 (URN)10.1109/EUMC.2008.4751484 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2009-09-24Bibliographically approved
    3. Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
    Open this publication in new window or tab >>Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
    2008 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 52, no 5, p. 740-744Article in journal (Refereed) Published
    Abstract [en]

    The switching behavior of a previously fabricated and tested SiC transistor is studied in Class-C amplifier in TCAD simulation. The transistor is simulated for pulse input signals in Class-C power amplifier. The simulated gain (dB), power density (W/mm) and power added efficiency (PAE%) at 500 MHz, 1, 2 and 3 GHz was studied using computational TCAD load pull simulation technique. A Maximum PAE of 77.8% at 500 MHz with 45.4 dB power gain and power density of 2.43 W/mm is achieved. This technique allows the prediction of switching response of the device for switching amplifier Classes (Class-C–F) before undertaking an expensive and time consuming device fabrication. The beauty of this technique is that, we need no matching and other lumped element networks for studying the large signal behavior of RF and microwave transistors.

    Keywords
    Pulse, Class-C, Power amplifier, New technique, Silicon carbide, MESFET
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13285 (URN)10.1016/j.sse.2007.09.022 (DOI)
    Available from: 2008-05-13 Created: 2008-05-13 Last updated: 2017-12-13Bibliographically approved
  • 80.
    Azam, Sher
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Jonsson, R.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Performance of SiC Microwave Transistors in Power Amplifiers2008In: Proc. of MRS Symposium on wide bandgap semiconductor electronics 8, 2008, p. 203-208Conference paper (Refereed)
    Abstract [en]

    The performance of SiC microwave power transistors is studied in fabricated class-AB power amplifiers and class-C switching power amplifier using physical structure of an enhanced version of previously fabricated and tested SiC MESFET. The results for pulse input in class-C at 1 GHz are; efficiency of 71.4 %, power density of 1.0 W/mm. The switching loss was 0.424 W/mm. The results for two class-AB power amplifiers are; the 30-100 MHz amplifier showed 45.6 dBm (∼ 36 W) output powers at P1dB, at 50 MHz. The power added efficiency (PAE) is 48 % together with 21 dB of power gain. The maximum output power at P1dB at 60 V drain bias and Vg= -8.5 V was 46.7 dBm (∼47 W). The typical results obtained in 200-500 MHz amplifier are; at 60 V drain bias the P1dB is 43.85 dBm (24 W) except at 300 MHz where only 41.8 dBm was obtained. The maximum out put power was 44.15 dBm (26 W) at 500 MHz corresponding to a power density of 5.2 W/mm. The PAE @ P1dB [%] at 500 MHz is 66 %.

  • 81.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, R.
    Swedish Defense Research Agency (FOI), SE-581 11, Linköping, Sweden.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Broadband Power Amplifier performance of SiC MESFET and CostEffective SiGaN HEMTManuscript (preprint) (Other academic)
    Abstract [en]

    This paper describes the broadband power amplifier performance of two differentwide band gap technology transistors at 0.7 to 1.8 GHz using cost effective NitronexGaN HEMT on Silicon (Si) and Cree Silicon Carbide MESFET. The measured resultsfor GaN amplifier are; maximum output power at Vd = 28 V is 42.5 dBm (~18 W), amaximum PAE of 39 % and a maximum gain of 19.5 dB is obtained. The measuredmaximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W),with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd = 66 V at700 MHz for SiC MESFET amplifier the Pmax was 42.2 dBm (~16.6 W) with a PAE of34.4 %.

  • 82.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, R,
    Swedish Defense Research Agency (FOI), SE-581 11, Linköping, Sweden.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    High Power, High Efficiency SiC Power Amplifier for Phased ArrayRadar and VHF ApplicationsManuscript (preprint) (Other academic)
    Abstract [en]

    Wide band gap semiconductor (SiC & GaN) based power amplifiers offer severalsystem critical advantages such as less current leakage, better stability at high temperatureand easier impedance matching. This paper describes the design and fabrication of a singlestageclass-AB power amplifier for 30 to 100 MHz using SiC Schottky gate MetalSemiconductor Field Effect Transistor (MESFET). The maximum output power achieved is46.2 dBm (~42 W) at 50 V DC supply voltage at the drain. The maximum power gain is 21dB and a maximum PAE of 62 %. The amplifier performance was also checked at a higherdrain bias of 60 V at 50 MHz. At this bias voltage the maximum output power was 46.7dBm (~47 W) with a power gain of 21 dB and a maximum PAE of 42.7 %. An averageOIP3 of 54 dBm have been achieved for this amplifier.

  • 83.
    Azam, Sher
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Jonsson, R.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    The limiting frontiers of maximum DC voltage at drain of SiC microwave power transistors in case of Class A power amplifiers2007In: International Semiconductor Device Research Symposium 2007 ISDRS-07,2007, IEEE , 2007Conference paper (Refereed)
    Abstract [en]

       

  • 84.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Fritzin, Jonas
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Alvandpour, Atila
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    High Power, Single Stage SiGaN HEMT Class E Power Amplifier at GHz Frequencies2010In: IEEE International Bhurban Conference on Applied Sciences and Technology, IEEE , 2010Conference paper (Refereed)
  • 85.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Swedish Defense Research Agency (FOI), Box 1165, SE-581 11 Linkoping, Sweden.
    Fritzin, Jonas
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Alvandpour, Atila
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    High Power, Single Stage SiGaN HEMT Class EPower Amplifier at GHz FrequenciesManuscript (preprint) (Other academic)
    Abstract [en]

    A high power single stage class E power amplifier is implemented with lumped elements at 0.89-1.02GHz using Silicon GaN High Electron Mobility Transistor as an active device. The maximum drain efficiency (DE) and power added efficiency (PAE) of 67 and 65 % respectively is obtained with a maximum output power of 42.2 dBm (~ 17 W) and amaximum power gain of 15 dB. We obtained good results at all measured frequencies.

  • 86.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Swedish Defense Research Agency (FOI), Box 1165, SE-581 11 Linköping, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies2008In: IEEE European Microwave Week, October 10-15, Amsterdam, The Netherlands, 2008, p. 444-447Conference paper (Refereed)
    Abstract [en]

    This paper describes the design, fabrication and measurement of two single-stage class-AB power amplifiers covering the frequency band from 0.7-1.8 GHz using a SiC MESFET and a GaN HEMT. The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32% and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4%. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34% and a power gain above 10 dB. The results for SiC amplifier are better than for GaN amplifier for the same 10-W transistor.

  • 87.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, Rolf
    Swedish Defense Research Agency (FOI), Box 1165, SE-581 11 Linköping, Sweden.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET2006In: Microwave Conference, 2006. APMC 2006. Asia-Pacific December 12-15, 2006, p. 441-444Conference paper (Refereed)
    Abstract [en]

    This paper describes a single-stage 26 W negative feedback power amplifier, covering the frequency range 200-500 MHz using a 6 mm gate width SiC lateral epitaxy MESFET. Typical results at 50 V drain bias for the whole band are, around 22 dB power gain, around 43 dBm output power, minimum power added efficiency at P1 dB is 47% at 200 MHz and maximum 60% at 500 MHz and the IMD3 level at 10 dB back-off from P1 dB is below -45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66% PAE.

  • 88.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Jonsson, Rolr
    Swedish Defense Research Agency (FOI), SE-581 11, Linköping, Sweden.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Comparison of Two GaN TransistorsTechnology in Broadband Power AmplifiersManuscript (preprint) (Other academic)
    Abstract [en]

    This paper compares the performance of two different GaN technology transistors(GaN HEMT on Silicon substrate (PA1) and GaN on SiC PA2) utilized in two broadbandpower amplifiers at 0.7-1.8 GHz. The study explores the broadband power amplifierpotential of both GaN HEMT technologies for Phased Array Radar (PAR) and electronicswarfare (EW) systems. The measured maximum output power for PA1 is 42.5 dBm(~18 W) with a maximum PAE of 39 % and a gain of 19.5 dB. While the measuredmaximum output power for PA2 is 40 dBm with PAE of 35 % and a power gain slightlyabove 10 dB. We obtained high power, gain, wider band width and unconditionalstability without feedback for amplifier based on GaN HEMT technology fabricated on Sisubstrate.

  • 89.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    A New Load Pull TCAD Simulation Technique for Class D, E & FSwitching Characteristics of TransistorsManuscript (preprint) (Other academic)
    Abstract [en]

    We have further developed a computational load pull simulation technique inTCAD. It can be used to study the Class-D, E & F switching response of the transistors. Westudied our enhanced version of previously fabricated and tested SiC transistor. Thesimulated Gain (dB), Power density (W/mm), switching loss (W/mm) and power addedefficiency (PAE %) at 500 MHz were studied using this technique. A PAE of 84 % at500MHz with 26 dB Power gain and power density of 2.75 W/mm is achieved. Thistechnique allows the prediction of switching response of the device before undertaking anexpensive and time-consuming device fabrication. The beauty of this technique is that, weneed no matching and other lumped element networks to study the large signal switchingbehavior of RF and microwave transistors.

  • 90.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD2008In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 52, no 5, p. 740-744Article in journal (Refereed)
    Abstract [en]

    The switching behavior of a previously fabricated and tested SiC transistor is studied in Class-C amplifier in TCAD simulation. The transistor is simulated for pulse input signals in Class-C power amplifier. The simulated gain (dB), power density (W/mm) and power added efficiency (PAE%) at 500 MHz, 1, 2 and 3 GHz was studied using computational TCAD load pull simulation technique. A Maximum PAE of 77.8% at 500 MHz with 45.4 dB power gain and power density of 2.43 W/mm is achieved. This technique allows the prediction of switching response of the device for switching amplifier Classes (Class-C–F) before undertaking an expensive and time consuming device fabrication. The beauty of this technique is that, we need no matching and other lumped element networks for studying the large signal behavior of RF and microwave transistors.

  • 91.
    Azam, Sher
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Svensson, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Electrical Engineering, Electronic Devices.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Designing of high efficiency power amplifier based on physical model of SiC MESFET in TCAD.2007In: International Bhurban conference on applied sciences technology.,2001, 2007Conference paper (Refereed)
    Abstract [en]

       

  • 92.
    Azam, Sher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Svensson, Christer
    Linköping University, Department of Electrical Engineering, Electronic Devices. Linköping University, The Institute of Technology.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Jonsson, R.
    Swedish Defence Research Agency.
    Comparison of Two GaN Transistor Technologies in Broadband Power Amplifiers2010In: MICROWAVE JOURNAL, ISSN 0192-6225, Vol. 53, no 4, p. 184-192Article in journal (Refereed)
    Abstract [en]

    This article compares the performance of two different GaN transistor technologies, GaN HEMT on silicon substrate (PA1) and GaN on SiC (PA2), utilized in two broadband power amplifiers operating at 0.7 to 1.8 GHz. The study explores the broadband power amplifier potential of both GaN HEMT technologies for phased-array radar (PAR) and electronic warfare (EW) systems. The measured maximum output power for PA1 is 42.5 dBm (18 W) with a maximum PAE of 66 percent and a gain of 19.5 dB. The measured maximum output power for PA2 is 40 dBm with a PAE of 37 percent and a power gain slightly above 10 dB. The high power gain, ME, wider bandwidth and unconditional stability was obtained without feedback for the amplifier based on GaN HEMT technology, fabricated on Si substrate.

  • 93. Baier, M.H.
    et al.
    Malko, A.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pelucchi, E.
    Kapon, E.
    Electrical and optical excitation schemes for pyramidal quantum dot single photon emitters2005In: Conference in Lasers and Electro-Optics CLEO,2005, 2005Conference paper (Other academic)
  • 94. Baier, M.H.
    et al.
    Malko, A.
    Pelucchi, E.
    Karlsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Oberli, D.Y.
    Kapon, E.
    Single photon emitters based on InGaAs/AlGaAs quantum dots grown by MOVPE in inverted pyramids2005In: 11th European Workshop on MOVPE,2005, 2005Conference paper (Other academic)
  • 95.
    Baker, A M R
    et al.
    University of Oxford, England .
    Alexander-Webber, J A
    University of Oxford, England .
    Altebaeumer, T
    University of Oxford, England .
    Janssen, T J B M
    National Phys Lab, England .
    Tzalenchuk, A
    National Phys Lab, England .
    Lara-Avila, S
    Chalmers, Sweden .
    Kubatkin, S
    Chalmers, Sweden .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lin, C-T
    Academic Sinica, Taiwan .
    Li, L-J
    Academic Sinica, Taiwan .
    Nicholas, R J
    University of Oxford, England .
    Weak localization scattering lengths in epitaxial, and CVD graphene2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 23, p. 235441-Article in journal (Refereed)
    Abstract [en]

    Weak localization in graphene is studied as a function of carrier density in the range from 1 x 10(11) cm(-2) to 1.43 x 10(13) cm(-2) using devices produced by epitaxial growth onto SiC and CVD growth on thin metal film. The magnetic field dependent weak localization is found to be well fitted by theory, which is then used to analyze the dependence of the scattering lengths L-phi, L-i, and L-* on carrier density. We find no significant carrier dependence for L-phi, a weak decrease for L-i with increasing carrier density just beyond a large standard error, and a n(-1/4) dependence for L-*. We demonstrate that currents as low as 0.01 nA are required in smaller devices to avoid hot-electron artifacts in measurements of the quantum corrections to conductivity. DOI: 10.1103/PhysRevB.86.235441

  • 96.
    Baker, A M R
    et al.
    University of Oxford, England .
    Alexander-Webber, J A
    University of Oxford, England .
    Altebaeumer, T
    University of Oxford, England .
    McMullan, S D.
    University of Oxford, England .
    Janssen, T J B M
    National Phys Lab, England .
    Tzalenchuk, A
    National Phys Lab, England .
    Lara-Avila, S
    Chalmers, Sweden .
    Kubatkin, S
    Chalmers, Sweden .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lin, C-T
    Academic Sinica, Taiwan .
    Li, L-J
    Academic Sinica, Taiwan .
    Nicholas, R J.
    University of Oxford, England .
    Energy loss rates of hot Dirac fermions in epitaxial, exfoliated, and CVD graphene2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 4, p. 045414-Article in journal (Refereed)
    Abstract [en]

    Energy loss rates for hot carriers in graphene have been measured using graphene produced by epitaxial growth on SiC, exfoliation, and chemical vapor deposition (CVD). It is shown that the temperature dependence of the energy loss rates measured with high-field damped Shubnikov-de Haas oscillations and the temperature dependence of the weak localization peak close to zero field correlate well, with the high-field measurements understating the energy loss rates by similar to 40% compared to the low-field results. The energy loss rates for all graphene samples follow a universal scaling of T-e(4) at low temperatures and depend weakly on carrier density proportional to n(-1/2), evidence for enhancement of the energy loss rate due to disorder in CVD samples.

  • 97.
    Bakoglidis, Konstantinos D.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Schmidt, Susann
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Garbrecht, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ivanov, Ivan G.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Low-temperature growth of low friction wear-resistant amorphous carbon nitride thin films by mid-frequency, high power impulse, and direct current magnetron sputtering2015In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 33, no 5, article id 05E112Article in journal (Refereed)
    Abstract [en]

    Amorphous carbon nitride (a-CNx) thin films were deposited on steel AISI52100 and Si(001) substrates using mid-frequency magnetron sputtering (MFMS) with an MF bias voltage, high power impulse magnetron sputtering (HiPIMS) with a synchronized HiPIMS bias voltage, and direct current magnetron sputtering (DCMS) with a DC bias voltage. The films were deposited at a low substrate temperature of 150 °C and a N2/Ar flow ratio of 0.16 at the total pressure of 400 mPa. The negative bias voltage (Vs) was varied from 20 V to 120 V in each of the three deposition modes. The microstructure of the films was characterized by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), while the film morphology was investigated by scanning electron microscopy (SEM). All films possessed amorphous microstructure with clearly developed columns extending throughout the entire film thickness. Layers grown with the lowest substrate bias of 20 V exhibited pronounced intercolumnar porosity, independent of the technique used. Voids closed and dense films formed at Vs ≥ 60 V, Vs ≥ 100 V and Vs = 120 V for MFMS, DCMS and HiPIMS, respectively. X-ray photoelectron spectroscopy (XPS) revealed that the nitrogen-to-carbon ratio, N/C, of the films ranged between 0.2 and 0.24. Elastic recoil detection analysis (ERDA) showed that Ar content varied between 0 and 0.8 at% and increases as a function of Vs for all deposition techniques. All films exhibited compressive residual stress, σ, which depends on the growth method; HiPIMS produces the least stressed films with stress between – 0.4 and – 1.2 GPa for all Vs values, while for CNx films deposited by MFMS σ = – 4.2 GPa. Nanoindentation showed a significant increase in film hardness and reduced elastic modulus with increasing Vs for all techniques. The harder films were produced by MFMS with hardness as high as 25 GPa. Low friction coefficients, between 0.05 and 0.06, were recorded for all films. Furthermore, CNx films produced by MFMS and DCMS at Vs = 100 V and 120 V presented a high wear resistance with wear coefficients of k ≤ 2.3 x 10-5 mm3/Nm.

  • 98.
    Bakoglidis, Konstantinos
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. SKF Engineering and Research Centre, Tribology and Lubrication Department, Nieuwegein, The Netherlands.
    Nedelcu, Ileana
    SKF Engineering and Research Centre, Tribology and Lubrication Department, Nieuwegein, The Netherlands.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Meeuwenoord, Ralph
    SKF Engineering and Research Centre, Tribology and Lubrication Department, Nieuwegein, The Netherlands.
    Schmidt, Susann
    IHI Ionbond AG, Olten, Switzerland.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ehret, Pascal
    SKF Engineering and Research Centre, Tribology and Lubrication Department, Nieuwegein, The Netherlands.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rolling performance of carbon nitride-coated bearing components in different lubrication regimes2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 114, p. 141-151Article in journal (Refereed)
    Abstract [en]

    The performance of carbon nitride (CN) coated roller bearings is investigated, using a micropitting rig. The rolling performance is evaluated using Stribeck test, with a continuously varying rolling speed (0.2 - 2 m/s). Rolling contact fatigue tests with constant speeds (0.5, 1, 2, and 3.5 m/s) are also conducted in order to study the high-cycle performance of the rollers. The obtained Stribeck curve shows that the presence of coatings eliminates run-in, resulting in low friction coefficients (similar to 0.08). Raman spectroscopy, performed at the wear tracks, reveals that CNx maintain stable chemical state. Coatings show abrasion although the wear rate is not detrimental for the performance of the rollers, since a CNx to-steel contact is retained during the entire rolling contact fatigue test.

  • 99.
    Balasubramanian, T
    et al.
    MAX-Lab, Lund University, Lund, Sweden.
    Johansson, Leif
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Glans, P. -A
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Silkin, VM
    Donostia International Physics Center (DIPC), San Sebastián/Donostia, Basque Country, Spain.
    Chulkov, EV
    Donostia International Physics Center (DIPC), San Sebastián/Donostia, Basque Country, Spain.
    Echenique, PM
    Donostia International Physics Center (DIPC), San Sebastián/Donostia, Basque Country, Spain.
    Surface electronic band structure and (A)over-bar surface state lifetimes at the Be(10(1)over-bar-0) surface: Experiment and theory2001In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 20Article in journal (Refereed)
    Abstract [en]

    The surface electronic band structure of the Be(10(1) over bar 0) surface is experimentally determined by angle-resolved photoemission and calculated by using density-functional theory. The experimental results agree well with the calculations, except for the fact that we were only able to resolve three surface states in the gap at (L) over bar, instead of four as predicted by the calculations. Through the temperature-dependent study, the phonon contribution subtracted width (h times inverse lifetime) of the shallow surface state at (A) over bar is found to be 51 +/- 8 meV. This is compared with the electron-electron interaction contribution to the width (53 meV) of the shallow surface state at A obtained from model potential calculations.

  • 100.
    Bano, Nargis
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Hussain, I
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ul Wahab, Qamar
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kwack, H S
    CEA, CNRS.
    Le Si Dang, D
    CEA, CNRS.
    Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC2010In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 130, no 6, p. 963-968Article in journal (Refereed)
    Abstract [en]

    Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors.

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