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  • 1.
    Beshkova, Milena
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Zakhariev, Z
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Sublimation epitaxy of AIN layers on 4H-SiC depending on the type of crucible2003In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 14, no 10-12, p. 767-768Article in journal (Refereed)
    Abstract [en]

    Epitaxial layers of aluminum nitride less than or equal to335 mum thick have been grown attemperatures of 1900 and 2100degreesC on 10 x 10 mm(2) (0001)-oriented alpha(4H) silicon carbide (SiC), with growth times of 1 and 4h, via sublimation-recondensation in a RF-heated graphite furnace. The source material was polycrystalline AIN. The sublimation process was performed in three types of graphite (C) crucible: C-1, C-2 with inner diameters of 35 and 51 mm, respectively, and C-3 with the same inner diameter as C-1, but coated with a layer of TaC. The surface morphology reflects the hexagonal symmetry of the substrate, suggesting an epitaxial growth for samples grown in C-1 and C-3 crucibles for all growth conditions. The same symmetry is observed for AIN layers grown in the C-2 crucible, but only at 2100degreesC. X-ray diffraction analyses confirm the epitaxial growth of AIN samples with the expected hexagonal symmetry. A high-resolution X-ray diffractometer was used to assess the quality of the single crystals. A full width at half maximum of 242 arcsec was achieved for an AIN layer grown in the crucible coated with TaC. (C) 2003 Kluwer Academic Publishers.

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

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

  • 3.
    Lankinen, A.
    et al.
    Helsinki Univ Technol, Micro & Nanosci Lab, Espoo 02015, Finland.
    Lang, T.
    Helsinki Univ Technol, Micro & Nanosci Lab, Espoo 02015, Finland.
    Suihkonen, S.
    Helsinki Univ Technol, Micro & Nanosci Lab, Espoo 02015, Finland.
    Svensk, O.
    Helsinki Univ Technol, Micro & Nanosci Lab, Espoo 02015, Finland.
    Saynatjoki, A.
    Helsinki Univ Technol, Micro & Nanosci Lab, Espoo 02015, Finland.
    Tuomi, T. O.
    Helsinki Univ Technol, Micro & Nanosci Lab, Espoo 02015, Finland.
    McNally, P. J.
    Dublin City Univ, Res Inst Networks & Commun Engn, Dublin 9, Ireland.
    Odnoblyudov, M.
    OptoGaN Oy, Espoo 02150, Finland.
    Bougrov, V.
    OptoGaN Oy, Espoo 02150, Finland.
    Danilewsky, A. N.
    Univ Freiburg, Inst Kristallog, D-79104 Freiburg, Germany.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Simon, R.
    ANKA, Inst Synchrotron Radiat, Karlsruhe, Germany.
    Dislocations at the interface between sapphire and GaN2008In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 19, no 2, p. 143-148Article in journal (Refereed)
    Abstract [en]

    GaN layers grown by metal organic vapour phase epitaxy on sapphire were imaged by synchrotron radiation X-ray topography. The threading dislocations could not be resolved in the topographs due to their high density, but a smaller density of about 10(5) cm(-2) defects were seen in the interface between GaN and sapphire by utilizing large-area back-reflection topography for the sapphire substrates. The misfit dislocation images in the topographs form a well-resolved cellular network, in which the average cell size is roughly 30 mu m. Different cell shapes in the misfit dislocation networks are observed on different samples. Also, images of small-angle grains of similar size were found in transmission section topographs of the GaN layers.

  • 4.
    Myrberg, T
    et al.
    Chalmers.
    Jacob, A P
    Chalmers.
    Nour, Omer
    Chalmers.
    Friesel, M
    Chalmers.
    Willander, Magnus
    Chalmers.
    Patel, C J
    University of North Carolina.
    Campidelli, Y
    STMicroelectronics, Crolles-Cedex, France.
    Hernandez, C
    STMicroelectronics, Crolles-Cedex, France.
    Kermarrec, O
    STMicroelectronics, Crolles-Cedex, France.
    Bensahel, D
    STMicroelectronics, Crolles-Cedex, France.
    Structural properties of relaxed Ge buffer layers on Si(001): effect of layer thickness and low temperature Si initial buffer2004In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 15, no 7, p. 411-417Article in journal (Refereed)
    Abstract [en]

    We have used the strain sensitive tool two-dimensional reciprocal space mapping (2D-RSM) and high resolution rocking curves (HR-RC) to assess the effect of the layer thickness and the influence of low temperature Si buffer on the properties of fully relaxed Ge on Si (0 0 1). The samples were grown by chemical vapor deposition in an ASM commercial reactor. As complementary measurements we have employed secondary ion mass spectrometry (SIMS) for chemical analysis, cross sectional transmission electron microscopy for quality assessment, and finally atomic force microscopy (AFM) for investigating the surface roughness. The investigated samples have a thickness ranging from 0.25 to 5.0 mum. In addition and for a 5.0 mum thick Ge layer, an initial low temperature Si (LT-Si) template was grown before the Ge epitaxy. The results indicate that high quality fully relaxed Ge layers have been achieved using the adopted growth procedure. Most of the improvement in crystalline quality was observed for Ge layers with thickness up to 1.5 mum. Above this thickness the observed crystalline quality improvement was negligible. The LT-Si buffer observed to be disadvantageous for pure relaxed Ge growth.

  • 5. Sabooni, M.
    et al.
    Esmaeili, M.
    Haratizadeh, H.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Amano, H.
    Dynamical study of the radiative recombination processes in GaN/AlGaN QWs2008In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 19, no SUPPL. 1Article in journal (Refereed)
    Abstract [en]

    The effects of the Si doping level on the recombination dynamics and carrier (exciton) localization in modulation-doped GaN/Al0.07 Ga0.93N multiple-quantum-well (MQW) structures were studied by means of photoluminescence (PL) and time-resolved PL measurements. All samples with different doping levels show a QW emission which is blue shifted with respect to the 3.48 eV PL peak from the GaN buffer layer. The decay time at the peak position remains nearly constant in the range of 320-420 ps at 2 K for all doping levels. For the undoped and low doped samples (3 × 1018 cm-3), which have less free electrons in the QWs, a non-exponential PL decay behaviour at 2 K is attributed to localized exciton recombination. The more highly doped samples (5 × 1018 cm-3 to 1020 cm-3) show almost exponential decay curves at 2 K, suggesting the recombination of free electrons and localized holes. The internal polarization-induced fields of the medium and highly-doped samples are partly screened by the electrons originating from the doping in the barriers. The emission peaks in time delayed PL spectra of these samples exhibit almost no shift as time evolves. Only the PL peak of the undoped and low-doped samples shows a redshift with time delay, related to the photogenerated carriers [1]. The decay time for the undoped sample shows non-exponential behaviour typical for localized excitons in III-N QWs. The same behaviour of decay time as a function of emission energy has been reported for InGaN QWs [2]. © Springer Science+Business Media, LLC 2008.

  • 6.
    Weman, Helge
    et al.
    Norwegian University of Science and Technology .
    Palmgren, Susanna
    Ecole Polytechnique Fédérale de Lausanne.
    Karlsson, Fredrik
    Ecole Polytechnique Fédérale de Lausanne.
    Rudra, A.
    Ecole Polytechnique Fédérale de Lausanne.
    Kapon, E.
    Ecole Polytechnique Fédérale de Lausanne.
    Dheeraj, D.L.
    Norwegian University of Science and Technology .
    Fimland, B.O.
    Norwegian University of Science and Technology .
    Harmand, J.C.
    CNRS.
    Semiconductor Quantum-Wires and Nano-Wires for optoelectronic Applications2009In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 20, no 1, p. S94-S101Article in journal (Refereed)
    Abstract [en]

    Exciton transfer between two parallel GaAs V-groove quantum wires (QWRs) or two planar quantum wells (QWs) separated by AlGaAs barriers ranging from 5.5 nm to 20 nm thickness is studied by photoluminescence (PL) and PL excitation (PLE) spectroscopy. It is found that the transfer is strongly reduced between the widely spaced QWRs as compared with QWs. We have also investigated the optical absorption in single QWRs embedded in an AlGaAs V-shaped channel waveguide. Using a combination of PLE and absorption measurements we construct the full dependence of absorption spectra on the linear polarization. Our studies reveal the importance of inter-subband mixing in determining the energies of the light-hole-like transitions and thus the QWR absorption. Finally we present recent results on the fabrication and structural characterization of GaAs and GaP nanowires (NWs) grown by molecular beam epitaxy (MBE) on GaAs(111)B and Si(111) substrates, using Au-catalyzed vapor–liquid–solid growth technique. It is shown that, apart from optimizing the NW growth parameters, substrate material and the procedure for preparing the substrate before the MBE growth play an important role in controlling the NWs.

  • 7.
    Willander, Magnus
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Friesel, M.
    Wahab, Q.-U.
    Straumal, B.
    Silicon carbide and diamond for high temperature device applications2006In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 17, no 1Article in journal (Refereed)
    Abstract [en]

    The physical and chemical properties of wide bandgap semiconductors silicon carbide and diamond make these materials an ideal choice for device fabrication for applications in many different areas, e.g. light emitters, high temperature and high power electronics, high power microwave devices, micro-electromechanical system (MEMS) technology, and substrates. These semiconductors have been recognized for several decades as being suitable for these applications, but until recently the low material quality has not allowed the fabrication of high quality devices. Silicon carbide and diamond based electronics are at different stages of their development. An overview of the status of silicon carbide's and diamond's application for high temperature electronics is presented. Silicon carbide electronics is advancing from the research stage to commercial production. The most suitable and established SiC polytype for high temperature power electronics is the hexagonal 4H polytype. The main advantages related to material properties are: its wide bandgap, high electric field strength and high thermal conductivity. Almost all different types of electronic devices have been successfully fabricated and characterized. The most promising devices for high temperature applications are pn-diodes, junction field effect transistors and thyristors. MOSFET is another important candidate, but is still under development due to some hidden problems causing low channel mobility. For microwave applications, 4H-SiC is competing with Si and GaAs for frequency below 10 GHz and for systems requiring cooling like power amplifiers. The unavailability of high quality defect and dislocation free SiC substrates has been slowing down the pace of transition from research and development to production of SiC devices, but recently new method for growth of ultrahigh quality SiC, which could promote the development of high power devices, was reported. Diamond is the superior material for high power and high temperature electronics. Fabrication of diamond electronic devices has reached important results, but high temperature data are still scarce. PN-junctions have been formed and investigated up to 400 °C. Schottky diodes operating up to 1000 °C have been fabricated. BJTs have been fabricated functioning in the dc mode up to 200 °C. The largest advance, concerning development of devices for RF application, has been done in fabrication of different types of FETs. For FETs with gate length 0.2 μm frequencies fT = 24.6 GHz, fmax(MAG) = 63 GHz and fmax(U) = 80 GHz were reported. Further, capacitors and switches, working up to 450 °C and 650 °C, respectively, have also been fabricated. Low resistant thermostable resistors have been investigated up to 800 °C. Temperature dependence of field emission from diamond films has been measured up to 950 °C. However, the diamond based electronics is still regarded to be in its infancy. The prerequisite for a successful application of diamond for the fabrication of electronic devices is availability of wafer diamond, i.e. large area, high quality, inexpensive, diamond single crystal substrates. A step forward in this direction has been made recently. Diamond films grown on multilayer substrate Ir/YSZ/Si(001) having qualities close those of homoepitaxial diamond have been reported recently. © Springer Science + Business Media, Inc. 2006.

  • 8.
    Ye, L L
    et al.
    Chalmers University of Technology.
    Thölén, A
    Chalmers University of Technology.
    Jacob, A P
    Chalmers University of Technology.
    Myrberg, T
    Chalmers University of Technology.
    Nour, Omer
    Chalmers University of Technology.
    Willander, Magnus
    Chalmers University of Technology.
    Structural roughness and interface strain properties in Si/SiO2/poly-Si1-xGex tri-layer system with ultrathin oxide2003In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 14, no 4, p. 247-254Article in journal (Refereed)
    Abstract [en]

    We have explored the microstructure and local interface strain in the poly-Si1-xGex/SiO2/Si tri-layer system with ultrathin oxides. High-resolution transmission electron microscopy (HRTEM) and high-resolution X-ray diffraction rocking curves (HR-RC) and two-dimensional reciprocal space mapping (2D-RSM) were the main characterization tools. The poly-Si1-xGex/SiO2/Si structures have x=0, 0.2, and 0.35 for ultrathin oxides (2.0-3.0 nm). The result shows that for the adopted growth process, the poly grain size depends very strongly on the Ge concentration, and it increases with increasing Ge mole fraction. In turn, this increase of the grain size in the poly-Si1-xGex/SiO2/Si reduces the strain in the film, which then affects the interface strain at the lower SiO2/Si interface. In addition, the presence of defects at the SiO2/Si interface was found to be greater for samples with no local interface strain.

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