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  • 151.
    Khranovskyy, Volodymyr
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Glushenkov, Alexey M.
    Deakin University, Australia .
    Chen, Y
    Deakin University, Australia .
    Khalid, A
    Trinity Coll Dublin, Ireland .
    Zhang, H
    Trinity Coll Dublin, Ireland .
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Crystal phase engineered quantum wells in ZnO nanowires2013Ingår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 24, nr 21Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the fabrication of quantum wells in ZnO nanowires (NWs) by a crystal phase engineering approach. Basal plane stacking faults (BSFs) in the wurtzite structure can be considered as a minimal segment of zinc blende. Due to the existing band offsets at the wurtzite (WZ)/zinc blende (ZB) material interface, incorporation of a high density of BSFs into ZnO NWs results in type II band alignment. Thus, the BSF structure acts as a quantum well for electrons and a potential barrier for holes in the valence band. We have studied the photoluminescence properties of ZnO NWs containing high concentrations of BSFs in comparison to high-quality ZnO NWs of pure wurtzite structure. It is revealed that BSFs form quantum wells in WZ ZnO nanowires, providing an additional luminescence peak at 3.329 eV at 4 K. The luminescence mechanism is explained as an indirect exciton transition due to the recombination of electrons in the QW conduction band with holes localized near the BSF. The binding energy of electrons is found to be around 100 meV, while the excitons are localized with the binding energy of holes of ~5 meV, due to the coupling of BSFs, which form QW-like structures.

  • 152.
    Khromov, Sergey
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Gregorius, D.
    Institut für Oberflächen- und Schichtanalytik IFOS GmbH, Kaiserslautern, Germany.
    Schiller, R.
    Institut für Oberflächen- und Schichtanalytik IFOS GmbH, Kaiserslautern, Germany.
    Lösch, J.
    Institut für Oberflächen- und Schichtanalytik IFOS GmbH, Kaiserslautern, Germany.
    Wahl, M.
    Institut für Oberflächen- und Schichtanalytik IFOS GmbH, Kaiserslautern, Germany.
    Kopnarski, M.
    Institut für Oberflächen- und Schichtanalytik IFOS GmbH, Kaiserslautern, Germany.
    Amano, A.
    Department of Electrical Engineering and Computer Science, Nagoya University, Chikusaku, Japan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Atom probe tomography study of Mg doped GaN layers2014Ingår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, nr 27, s. 275701-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atom probe tomography studies on highly Mg-doped GaN(0001) layers with concentrations 5×1019 cm-3 and 1×1020 cm-3 were performed. Mg cluster formation was observed only in the higher doped sample whereas in the lower doped sample the Mg distribution was homogeneous. CL measurements showed that the emission normally attributed to stacking faults was only present in the lower doped layers ([Mg] = 1.5×1019 and 5×1019 cm-3), but absent in the higher-doped layer, where Mg clusters were detected. Mg clusters are proposed to produce a screening effect thereby destroying the exciton binding on the SFs thus rendering them optically inactive.

  • 153.
    Khromov, Sergey
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hemmingsson, Carl
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Amano, H
    Nagoya University.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Luminescence related to high density of Mg-induced stacking faults in homoepitaxially grown GaN2011Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, nr 7, s. 075324-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of Mg doping on stacking fault (SF) formation in c-plane GaN grown by metal-organic chemical-vapor deposition has been studied for Mg concentration between 2 x 10(18) cm(-3) and 5 x 10(19) cm(-3). Transmission electron microscopy studies demonstrate a direct correlation between the increasing Mg content and the number of small (3-10-nm long) SFs present. The energy dispersive x-ray analysis (EDX) line profile of a SF shows that the Mg-impurity atom resides at a distance approximately 5 nm from the SF. Cathodoluminescence (CL) mapping reveals that the Mg-doped regions radiate at energies corresponding to known SF emission peaks. SF-related peaks in CL spectra show metastability, which may be attributed to transfer processes involving Mg acceptors and nearby associated SFs.

  • 154.
    Khromov, Sergey
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hemmingsson, Carl
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Effect of C-doping on near-band gap luminescence in bulk GaN substrates grown by halide vapor phase epitaxy2013Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Freestanding bulk C-doped GaN substrates grown by halide vapor phase epitaxy were studied by optical spectroscopy and electron microscopy. In cathodoluminescence (CL) the yellow line (YL) was more intense in samples with higher C content and stable in the temperature range 5-300 K. CL mapping in situ a scanning electron microscope revealed pitlike structure of the layers with higher YL intensity in the pits related to higher local oxygen incorporation. Near bandgap (NBG) emission studies of the pits revealed donor-bound excitons (DBE) with broad emission and no significant acceptor bound exciton (ABE) emission. Pit-free areas demonstrate two well-resolved ABEs with DBE quenched. Quenching of the DBE is explained by potential fluctuations in the vicinity of the carbon atoms in the pits-free regions lowering the ionization barrier for DBE.

  • 155.
    Khromov, Sergey
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hemmingsson, Carl
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Optical properties of C-doped bulk GaN wafers grown by halide vapor phase epitaxy2014Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, nr 22, s. 223503-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Freestanding bulk C-doped GaN wafers grown by halide vapor phase epitaxy are studied by optical spectroscopy and electron microscopy. Significant changes of the near band gap (NBG) emission as well as an enhancement of yellow luminescence have been found with increasing C doping from 5 × 1016 cm−3 to 6 × 1017 cm−3. Cathodoluminescence mapping reveals hexagonal domain structures (pits) with high oxygen concentrations formed during the growth. NBG emission within the pits even at high C concentration is dominated by a rather broad line at ∼3.47 eV typical for n-type GaN. In the area without pits, quenching of the donor bound exciton (DBE) spectrum at moderate C doping levels of 1–2 × 1017 cm−3 is observed along with the appearance of two acceptor bound exciton lines typical for Mg-doped GaN. The DBE ionization due to local electric fields in compensated GaN may explain the transformation of the NBG emission.

  • 156.
    Khromov, Sergey
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Avrutin, V.
    Department of Electrical Engineering and Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284, USA.
    Li, Xing
    Department of Electrical Engineering and Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284, USA.
    Morkoç, H.
    Department of Electrical Engineering and Physics Department, Virginia Commonwealth University, Richmond, Virginia 23284, USA.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Optical and structural studies of homoepitaxially grown m-plane GaN2012Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, nr 17, s. 172108-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on cathodoluminescence (CL) and transmission electron microscopy (TEM) studies of m-plane Mg-doped GaN layers grown by metal-organic vapor phase epitaxy (MOVPE). The layers contain basal plane and prismatic stacking faults (SFs) with a density of ~106 cm-1. Broad emission peaks commonly ascribed to SF were found to be insignificant in these samples. However, a set of quite strong and sharp lines were detected in the same spectral region 3.36-3.42 eV. The observed peaks are tentatively explained as excitons bound to some point defects by analogy with p-type GaAs, since donor-acceptor pair (DAP) recombination was ruled out by the CL mapping experiments.

  • 157.
    Khromov, Sergey
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Avrutin, V.
    Department of Electrical Engineering and Physics Department, Virginia Commonwealth University, Virginia, USA.
    Morkoc, H.
    Department of Electrical Engineering and Physics Department, Virginia Commonwealth University, Virginia, USA.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Correlation between Si doping and stacking fault related luminescence in homoepitaxial m-plane GaN2013Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, s. 192101-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Si-doped GaN layers grown by metal organic vapor phase epitaxy on m-plane GaN substrates were investigated by low-temperature cathodoluminescence (CL). We have observed stacking fault (SF) related emission in the range of 3.29–3.42 eV for samples with moderate doping, while for the layers with high concentration of dopants, no CL lines related to SFs have been noted. Perturbation of the SF potential profile by neighboring impurity atoms can explain localization of excitons at SFs, while this effect would vanish at high doping levels due to screening.

  • 158.
    Khromov, Sergey
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Persson, Per O A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Wang, X.
    Peking University, Peoples R China.
    Yoshikawa, A.
    Chiba University, Japan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Rosén, Johanna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Correlation between switching to n-type conductivity and structural defects in highly Mg-doped InN2015Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, nr 23, artikel-id 232102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of Mg doping on the microstructure of InN epitaxial films in relation to their free-charge carrier properties has been investigated by transmission electron microscopy (TEM) and aberration corrected scanning TEM. We observe a direct correlation between Mg concentration and the formation of stacking faults. The threading dislocation density is found to be independent of Mg concentration. The critical Mg concentration for the on-set of stacking faults formation is determined and found to correlate with the switch from p- to n-type conductivity in InN. Potential mechanisms involving stacking faults and point defect complexes are invoked in order to explain the observed conductivity reversal. Finally, the stacking faults are structurally determined and their role in the reduction of the free electron mobility in highly doped InN: Mg is discussed. (C) 2015 AIP Publishing LLC.

  • 159.
    Kroger, R.
    et al.
    Kröger, R., Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Paskova, T.
    Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Figge, S.
    Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Hommel, D.
    Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Rosenauer, A.
    Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Interfacial structure of a -plane GaN grown on r -plane sapphire2007Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, nr 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interface between a -plane GaN, grown by metal organic vapor phase epitaxy and hydride vapor phase epitaxy, and r -plane sapphire was investigated by transmission electron microscopy in [1-100] and [0001] zone axis orientations. The interfacial structure was well defined allowing a direct observation of the misfit dislocations in both orientations. An analysis of these dislocations revealed for the respective Burgers vectors a 13 <2-1-10> component in the {0002} planes and a 12 <0001> component in the {1-100} planes. In addition, the relative atomic column configurations in the GaN and sapphire were determined based on Bloch-wave simulations in comparison with the experimental images. © 2007 American Institute of Physics.

  • 160. Kröger, R.
    et al.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Figge, S.
    Hommel, D.
    Rosenauer, A.
    Defect structure of a-plane GaN grown by hydride and metal-organic vapor phase epitaxy on r-plane sapphire2007Ingår i: Proc. of the International Workshop on Nitride Semiconductors IWN2006,2006, Physica Status Solidi C, vol. 4: WILEYVCH Verlag GmbH & Co. KGaA , 2007, s. 2564-Konferensbidrag (Refereegranskat)
    Abstract [en]

      

  • 161.
    Larsson, Henrik
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Gogova, Daniela
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Kasic, A.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Yakimova, Rositsa
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Miskys, C. R.
    Walter Schottky Institut, Technische Universität Munchen, Germany.
    Stutzmann, M.
    Walter Schottky Institut, Technische Universität Munchen, Germany.
    Free-standing HVPE-GaN Layers2003Ingår i: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 0, nr 7, s. 1985-1988Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have grown GaN layers with a thickness up to 340 μm in an rf-heated vertical HVPE reactor with a bottom-fed design. The GaN layers were separated from the sapphire substrate by a LLO process. The free-standing GaN was investigated by HRXRD, AFM and low temperature CL. The FWHM values of the ω-scans are 96 and 129 arcsec for the (104) and (002) reflection, respectively, which indicates high crystalline quality. The c and a lattice parameters are determined as c = 0.51850 ± 0.00004 nm and a = 0.31890 ± 0.00004 nm, indicating stress free material. The etch pit density was estimated to be 1 × 107 cm−2. The used HVPE growth procedure together with the subsequent LLO are obviously capable to provide high-quality free-standing GaN material for further epitaxial overgrowth.

  • 162. Leon, R
    et al.
    Ibanez, J
    Marcinkevicius, S
    Siegert, J
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Chaparro, S
    Navarro, C
    Johnson, SR
    Zhang, YH
    Defect states in red-emitting InxAl1-xAs quantum dots2002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, nr 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 163. Leon, R
    et al.
    Nadeau, J
    Evans, K
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Electron irradiation effects on nanocrystal quantum dots used in bio-sensing applications2004Ingår i: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, nr 6, s. 3186-3192Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 164.
    Lindgren, D
    et al.
    Lund University, Solid State Physics and the Nanometer Structure Consortium, Sweden.
    Heurlin, M
    Lund University, Solid State Physics and the Nanometer Structure Consortium, Sweden.
    Kawaguchi, K
    Lund University, Solid State Physics and the Nanometer Structure Consortium, Sweden.
    Borgström, M T
    Lund University, Solid State Physics and the Nanometer Structure Consortium, Sweden.
    Pistol, M-E
    Lund University, Solid State Physics and the Nanometer Structure Consortium, Sweden.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan. Lund University, Sweden.
    Samuelson, L
    Lund University, Solid State Physics and the Nanometer Structure Consortium, Sweden.
    Gustafsson, A
    Lund University, Solid State Physics and the Nanometer Structure Consortium, Sweden.
    A luminescence study of doping effects in InP-based radial nanowire structures2013Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 471, nr 1, artikel-id 012040Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have used micro-photo- and cathodo-luminescence at low temperatures to study the effects of sulphur doping in InP and radial InP/InAs/InP structured nanowires. Samples with pure wurtzite crystal structure, with modulated wurtzite/zincblende crystal structure and with different radial InAs growth times were investigated. We observed a doping concentration gradient along the nanowires, the location of segments of different crystal structure and thickness fluctuations on the monolayer scale of the InAs layer.

  • 165.
    Linnarsson, M.
    et al.
    Royal Institute of Technology.
    Janzén, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kleverman, M.
    University of Lund.
    Thilderkvist, A.
    University of Lund.
    Electronic structure of the GaAs:MnGa center1997Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 55, nr 11, s. 6938-6944Artikel i tidskrift (Refereegranskat)
    Abstract [en]

      n/a

     

  • 166. Malinauskas, T.
    et al.
    Aleksiejunas, R.
    Jarasiunas, K.
    Beaumont, B.
    Gibart, P.
    Kakanakova-Georgieva, Anelia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Janzén, Erik
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Gogova, Daniela
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Heuken, M.
    All-optical characterization of carrier lifetimes and diffusion lengths in MOCVD-, ELO-, and HVPE- grown GaN2007Ingår i: Journal of Crystal Growth, Vol. 300, 2007, Vol. 300, nr 1, s. 223-227Konferensbidrag (Refereegranskat)
    Abstract [en]

    The metrological capability of the picosecond four-wave mixing (FWM) technique for evaluation of the photoelectrical properties of GaN heterostructures grown on sapphire, silicon carbide, and silicon substrates as well as of free-standing GaN films is demonstrated. Carrier recombination and transport features have been studied in a wide excitation, temperature, and dislocation density (from ∼1010 to 106 cm-2) range, exploring non-resonant refractive index modulation by a free carrier plasma. The studies allowed to establish the correlations between the dislocation density and the carrier lifetime, diffusion length, and stimulated emission threshold, to reveal a competition between the bimolecular and nonradiative recombination, and to verify the temperature dependence of bimolecular recombination coefficient in the 10-300 K temperature range. It was shown that the FWM technique is more advantageous than the time-resolved photoluminescence technique for determination of carrier lifetimes in high quality thick III-nitride layers. © 2006 Elsevier B.V. All rights reserved.

  • 167. Malinauskas, T
    et al.
    Jarasiunas, K
    Aleksiejunas, R
    Gogova, Daniela
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Beaumont, B
    Gibart, P
    Contribution of dislocations to carrier recombination and transport in highly excited ELO and HYPE GaN layers2006Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, nr 7, s. 1426-1430Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonequilibrium carrier dynamics has been investigated in ELO and HYPE grown GaN layers in a wide temperature and excitation range by using the time-resolved picosecond FWM technique. Carrier lifetime in the samples at 300 K increased up to 2.8-5.1 ns in accordance with the decreasing threading dislocation density from 4 x 10(7) cm(-2) (ELO) to mid 106 cm(-2) in HYPE layers. At T < 100 K, the hyperbolic shape of FWM kinetics indicated carrier density dependent radiative lifetimes, which gradually decreased at lower temperatures to a few hundreds of ps. The dominance of bimolecular recombination in HVPE layers at 10-40 K was demonstrated by the exposure characteristic of FWM, that has shown a sublinear growth of carrier density with excitation, N proportional to I-1/2. Numerical fitting of the set of FWM kinetics at various T confirmed the temperature dependence of bimolecular recombination coefficient B proportional to T-1/5 and provided its value B = 2 x 10(-11) cm(3)/s at 300 K and 3.2 x 10(-9) cm(3)/s at 9 K. The measured bipolar diffusion coefficients allowed determination of carrier diffusion length of 0.8-1 mu m at 300 K and its dependence on dislocation density and temperature. (c) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 168.
    Misheva, M.
    et al.
    Department of Physics, Sofia University, Sofia, Bulgaria.
    Larsson, Henrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Gogova, Daniela
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Positron annihilation study of HVPE grown thick GaN layers2005Ingår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, nr 5, s. 713-717Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single-crystalline GaN layers with a thickness up to 330 µm were grown by hydride vapor phase epitaxy on basal plane sapphire at gallium stable conditions in a bottom-fed vertical reactor at atmospheric pressure. Positron annihilation spectroscopy experiments were implemented in order to identify native point defects in the as-grown non-intentionally doped n-type GaN. Comparatively low concentrations of Ga vacancy related defects in the order of 1016 to 1017 cm–3 were extracted from the positron annihilation spectroscopy data. The Ga vacancy defect concentration was related to the intensity of the yellow photoluminescence band centered at 2.2 eV. The influence of the growth rate on the Ga vacancy related defect concentration was investigated. A trend of decreasing of the defect concentration with increasing of layer thickness is observed, which correlates with improving crystalline quality with the thickness.

  • 169.
    Mock, Alyssa
    et al.
    University of Nebraska, NE 68588 USA.
    Korlacki, Rafal
    University of Nebraska, NE 68588 USA.
    Briley, Chad
    University of Nebraska, NE 68588 USA.
    Darakchieva, Vanya
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Monemar, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten. Tokyo University of Agriculture and Technology, Japan.
    Kumagai, Yoshinao
    Tokyo University of Agriculture and Technology, Japan; Tokyo University of Agriculture and Technology, Japan.
    Goto, Ken
    Tokyo University of Agriculture and Technology, Japan; Tamura Corp, Japan.
    Higashiwaki, Masataka
    National Institute Informat and Commun Technology, Japan.
    Schubert, Mathias
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten. University of Nebraska, NE 68588 USA; University of Nebraska, NE 68588 USA; Leibniz Institute Polymer Research Dresden, Germany.
    Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic beta-Ga2O32017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 24, artikel-id 245205Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic beta-Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

  • 170.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bound excitons in GaN2001Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, nr 32, s. 7011-7026Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure of bound excitons in GaN is discussed, with reference to available optical data. Emphasis is given to the neutral-donor and neutralacceptor spectra, which are the most prominent ones in the experimental photoluminescence data. Two dominant donor bound excitons are observed with photoluminescence lines just above 3.47 eV at 2 K in unstrained samples, tentatively associated with Si and O shallow donors. Several acceptor bound excitons are present, the most prominent one with a photoluminescence line at about 3.466 eV is tentatively assigned to the Mg acceptor. We attempt an explanation of the available data from magneto-optical experiments on this line in terms of a spin-like acceptor hole, as observed in independent magnetic resonance data. Characteristic deep emissions related to P and As doping are reported, they may be interpreted in terms of isoelectronic bound excitons. Excitons bound to structural defects in GaN are also briefly discussed.

  • 171.
    Monemar, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Perspective on the development of III-nitrides for optical emitters2008Ingår i: Advances in Light emitting Materials / [ed] Bo Monemar,Martin Kittler ,Hermann Grimmeiss, Materials Science Forum Vol 590: Trans Tech Publications , 2008, s. 17-26Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    This special-topic volume‚ Advances in Light-Emitting Materials’, makes an important contribution to the field of silicon and III-nitride semiconductors. It begins with a brief history of visible-light emitting diodes. However, silicon is currently expanding from micro-electronics and into photonics. Due to its unsuitable band-gap, it has not previously been the material-of-choice for opto-electronic integration. That is now beginning to change and silicon devices have been developed which have the capability to emit, modulate, guide and detect light and which can be combined with microelectronics to form electronic and photonic integrated circuits. In particular, the performance of silicon-based light-emitters has made rapid progress during the last few years: the first paper describes the potential value of the D-band luminescence caused by dislocations in silicon and its use in infra-red light-emitters. Silicon-wafer direct-bonding, which  permits the controlled formation of dislocation networks, is described in detail in the next paper. Silicon and silicon-germanium light-emitting diodes (LED), which emit band-to-band radiation, are then described. This paper is followed by observations on the effect of carrier-confinement on the emission of the band-to-band radiation of LEDs fabricated in silicon-on-insulator form. Finally, MOS light-emitting devices, based upon rare-earth ion-implantation, are described. These structures exhibit efficient electroluminescence within the wavelengths ranging from UV to visible light. Altogether, this volume presents an in-depth review of this important topic.

  • 172.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Comment on "Fermi-edge singularity observed in a modulation-doped AlGaN/GaN heterostructure"2000Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 76, s. 655-Artikel i tidskrift (Refereegranskat)
  • 173.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Dalfors, J
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Sernelius, Bo
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Holtz, Per-Olof
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Amano, H
    Akasaki, I
    Radiative recombination in In0.15Ga0.85N/GaN multiple quantum well structures1999Ingår i: MRS Internet journal of nitride semiconductor research, ISSN 1092-5783, E-ISSN 1092-5783, Vol. 4, nr 16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a study of the radiative recombination in In0.15Ga0.85N/GaN multiple quantum well samples, where the conditions of growth of the InGaN quantum layers were varied in terms of growth temperature (< 800 degrees C) and donor doping. The photoluminescence peak position varies strongly (over a range as large as 0.3 eV) with delay time after pulsed excitation, but also with donor doping and with excitation intensity. The peak position is mainly determined by the Stark effect induced by the piezoelectric field. In addition potential fluctuations, originating from segregation effects in the InGaN material, from interface roughness, and the strain fluctuations related to these phenomena, play an important role, and largely determine the width of the emission. These potential fluctuations may be as large as 0.2 eV in the present samples, and appear to be important for all studied growth temperatures for the InGaN layers. Screening effects from donor electrons and excited electron-hole pairs are important, and account for a large part of the spectral shift with donor doping (an upward shift of the photoluminescence peak up to 0.2 eV is observed for a Si donor density of 2 x 10(18) cm(-3) in the well), with excitation intensity and with delay time after pulsed excitation (also shifts up to 0.2 eV). We suggest a two-dimensional model for electron- and donor screening in this case, which is in reasonable agreement with the observed data, if rather strong localization potentials of short range (of the order 100 Angstrom) are present. The possibility that excitons as well as shallow donors are impact ionized by electrons in the rather strong lateral potential fluctuations present at this In composition is discussed.

  • 174.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Buyanova, Irina
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Chen, Weimin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Wagner, Matthias
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Defects in Gallium Nitride1999Ingår i: International Workshop on Materials Science,1999, Proc. of the International Workshop on Materials Science 99, ed. by F. F. Bekker et al., Vol. 1: Hanoi National University Publishing House , 1999, s. 28-Konferensbidrag (Refereegranskat)
  • 175.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Chen, Weimin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    The 3.466 eV Bound Exciton in GaN2001Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 228, nr 2, s. 489-492Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 176.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Harati Zadeh, Hamid
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Holtz, Per-Olof
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Kamiyama, S.
    Iwaya, M.
    Amano, H.
    Akasaki, I.
    Influence of polarization fields and depletion fields on photoluminescence of AlGaN/GaN multiple quantum well structures2003Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 237, nr 1, s. 353-364Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on a detailed study of low temperature photoluminescence (PL) in Al0.07Ga0.93N/GaN multiple quantum wells (MQWs). The structures were grown on sapphire with the conventional low temperature AlN nucleation layer and thick GaN buffer layer. Several sets of 5 QW MQW samples were studied, one set with Si doping in the barriers up to or above the metallic limit. Nominally undoped MQW samples were also studied. The spectral behaviour of the doped samples was strongly affected by the near surface depletion field, causing overlap of different spectra from non-equivalent QWs. The QWs closest to the surface are presumably inactive in some samples, due to a very high depletion field. For the case of undoped samples, on the other hand, the near surface QWs are active and most prominent in the PL spectra. The structure from discrete well width variations is here resolved in the PL spectra. The results demonstrate that for structures with no additional capping layer both the depletion field and the polarisation fields need to be considered in the interpretation of experimental data. The theoretically estimated fields in this work are consistent with the experimental spectra. The presence of localisation even in the case of metallic samples, as observed by a constant PL decay time independent of doping, is discussed in terms of penetration of the hole wave functions into the AlGaN barriers. This localisation is also manifested in a sizeable LO phonon coupling strength in all samples studied.

  • 177.
    Monemar, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Khromov, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Paskov, Plamen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Bergman, Peder
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hemmingsson, Carl
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Amano, Hiroshi
    Nagoya University, Japan.
    Avrutin, Vitaliy
    Virginia Commonwealth University, VA USA.
    Li, Xing
    Virginia Commonwealth University, VA USA.
    Morkoc, Hadis
    Virginia Commonwealth University, VA USA.
    Luminescence of Acceptors in Mg-Doped GaN2013Ingår i: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 52, nr 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent photoluminescence (PL) data for Mg-doped GaN at 2 K are discussed, with reference to published theoretical calculations of the electronic level structure. It is concluded that the typical PL peaks at 3.466 eV (acceptor bound exciton ABE1) and the broader 3.27 eV donor-acceptor pair (DAP) PL are the expected standard PL signatures of the substitutional Mg acceptor. Additional broader peaks at 3.455 eV (ABE2) and 3.1 eV are suggested to be related to the same acceptors perturbed by nearby basal plane stacking faults. The low temperature metastability of PL spectra is assigned to a nonradiative metastable deep level.

  • 178.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Kittler, M.Grimmeiss, H.
    Advances in Light emitting Materials2008Samlingsverk (redaktörskap) (Övrigt vetenskapligt)
    Abstract [en]

      This special-topic volume‚ Advances in Light-Emitting Materials’, makes an important contribution to the field of silicon and III-nitride semiconductors. It begins with a brief history of visible-light emitting diodes. However, silicon is currently expanding from micro-electronics and into photonics. Due to its unsuitable band-gap, it has not previously been the material-of-choice for opto-electronic integration. That is now beginning to change and silicon devices have been developed which have the capability to emit, modulate, guide and detect light and which can be combined with microelectronics to form electronic and photonic integrated circuits.                   read more...

    In particular, the performance of silicon-based light-emitters has made rapid progress during the last few years: the first paper describes the potential value of the D-band luminescence caused by dislocations in silicon and its use in infra-red light-emitters. Silicon-wafer direct-bonding, which  permits the controlled formation of dislocation networks, is described in detail in the next paper. Silicon and silicon-germanium light-emitting diodes (LED), which emit band-to-band radiation, are then described. This paper is followed by observations on the effect of carrier-confinement on the emission of the band-to-band radiation of LEDs fabricated in silicon-on-insulator form. Finally, MOS light-emitting devices, based upon rare-earth ion-implantation, are described. These structures exhibit efficient electroluminescence within the wavelengths ranging from UV to visible light.

    Altogether, this volume presents an in-depth review of this important topic.

  • 179.
    Monemar, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Larsson, Henrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Hemmingsson, Carl
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Ivanov, Ivan Gueorguiev
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Gogova, Daniela
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Growth of thick GaN layers with hydride vapour phase epitaxy2005Ingår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, nr 1, s. 17-31Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we describe recent experimental efforts to produce high quality thick (⩾300 μm) GaN layers on sapphire, the removal of such a layer from the sapphire substrate, and the properties of the so obtained free-standing GaN material. The growth process is described in some detail in the vertical reactor geometry used in this work. Defects like dislocations, micro-cracks and pits produced during growth are discussed, along with procedures to minimize their concentration on the growing surface. The laser lift-off technique is shown to be a feasible technology, in particular if a powerful laser with a large spot size can be used. A major problem with the free-standing material is the typically large bowing of such a wafer, due to the built in defect concentrations near the former GaN-sapphire interface. This bowing typically causes a rather large width of the XRD rocking curve of the free-standing material, while optical data confirm virtually strain free material of excellent quality at the top surface.

  • 180.
    Monemar, Bo
    et al.
    Solid State Physics, Lund University, Lund, Sweden.
    Ohlsson, B. Jonas
    GLO AB, Lund, Sweden.
    Gardner, Nathan F.
    GLO-USA Inc., Sunnyvale, California, USA.
    Samuelson, Lars
    GLO-USA Inc., Sunnyvale, California, USA.
    Chapter Seven - Nanowire-Based Visible Light Emitters, Present Status and Outlook2016Ingår i: Semiconductors and Semimetals: Semiconductor Nanowires II: Properties and Applications / [ed] Shadi A. Dayeh, Anna Fontcuberta i Morral; Jagadish, Chennupati, Elsevier, 2016, Vol. 94, s. 227-271Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    So far, the semiconductor nanowire research area has mainly delivered results on growth procedures and related material properties. As the development lately has been successful in producing novel nanowire-based structures for optical or electronic applications, the time is ripe to review the device work that has been done and in some cases has produced devices ready for the market. In this chapter, we shall review the specific area of nanowire-based LEDs (NW-LEDs) for visible light, including the application area of “solid state lighting” (SSL). A brief review of the progress in the area of visible light LEDs over the last half century is presented, this also mentions some of the progress made in the planar technology so far. The most successful way of producing white light is still based on the use of phosphors, just like in the present compact fluorescence lamps (CFLs). The reason for this is the high efficiency (external quantum efficiency &gt; 80%) possible at low currents in the violet planar InGaN-based LEDs used to excite the phosphors. These LEDs are presently mainly produced on foreign substrates, leading to a high dislocation density (DD) and a sizeable droop at high injection currents (25–40%). This droop and the down conversion energy loss in the phosphors (20–25%) has motivated the interest for a phosphor-less white light source based on direct mixing of light of different wavelength (such as red, green, and blue; RGB). To be competitive, this solution must be based on highly efficient LEDs for all RGB (red, green, and blue) colors. Since NW-LED structures can be produced basically free of structural defects (even if grown on a foreign substrate), the idea of using the RGB mixing concept for the production of white light sources with an ultimately higher efficiency than for the phosphor-based lamps is a major technical target for a second generation of light sources in the SSL field. Basic concepts behind the design and optical properties of NW-LED structures are discussed in this chapter, with emphasis on the present developments of III-nitride-based structures. The growth procedure relevant for such NW-LED structures is reported in some detail, specifically the core–shell configuration readily produced with metalorganic vapor phase epitaxy (MOVPE). The first generation processing technology for NW-LED structures is briefly described; this is naturally quite different from the established routines for planar LED chips. Experimental data for nitride-based NW-LEDs for blue, green, and even longer wavelengths are given in terms of radiative efficiencies, light outcoupling, droop, and long-term reliability. The experience so far is that for these NW-based emitters, efficiencies can be obtained that are close to those for the corresponding planar LEDs. There are still problems with the reproducibility of the radiative output, as well as a significant droop that would not be expected for m-plane emitters. More work is needed to pinpoint the cause of these problems. Finally, we briefly discuss various applications (also other than white lamps) where the NW-LEDs may have a specific advantage.

  • 181.
    Monemar, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Paskov, Plamen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Luminescence Studies of Impurities and Defects in III-Nitride Semiconductors2010Ingår i: Handbook of Luminescent Semiconductor Materials / [ed] Leah Bergman, Jeanne L McHale, CRC Press, 2010, s. 169-190Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    Photoluminescence spectroscopy is an important approach for examining the optical interactions in semiconductors and optical devices with the goal of gaining insight into material properties. With contributions from researchers at the forefront of this field, Handbook of Luminescent Semiconductor Materials explores the use of this technique to study semiconductor materials in a variety of applications, including solid-state lighting, solar energy conversion, optical devices, and biological imaging.

    After introducing basic semiconductor theory and photoluminescence principles, the book focuses on the optical properties of wide-bandgap semiconductors, such as AlN, GaN, and ZnO. It then presents research on narrow-bandgap semiconductors and solid-state lighting. The book also covers the optical properties of semiconductors in the nanoscale regime, including quantum dots and nanocrystals.

    This handbook explains how photoluminescence spectroscopy is a powerful and practical analytical tool for revealing the fundamentals of light interaction and, thus, the optical properties of semiconductors. The book shows how luminescent semiconductors are used in lasers, photodiodes, infrared detectors, light-emitting diodes, solid-state lamps, solar energy, and biological imaging.

    Show more Show less

  • 182.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Bergman, JP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Nagoya, Aichi, Japan Meijo Univ, High Tech Res Ctr, Nagoya, Aichi, Japan.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Darakchieva, Vanya
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Iwaya, M
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Nagoya, Aichi, Japan Meijo Univ, High Tech Res Ctr, Nagoya, Aichi, Japan.
    Kamiyama, S
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Nagoya, Aichi, Japan Meijo Univ, High Tech Res Ctr, Nagoya, Aichi, Japan.
    Amano, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Nagoya, Aichi, Japan Meijo Univ, High Tech Res Ctr, Nagoya, Aichi, Japan.
    Akasaki, I
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect & Elect Engn, Nagoya, Aichi, Japan Meijo Univ, High Tech Res Ctr, Nagoya, Aichi, Japan.
    Photoluminescence in n-doped In0.1Ga0.9N/In0.01Ga0.99N multiple quantum wells2002Ingår i: MRS Internet journal of nitride semiconductor research, ISSN 1092-5783, E-ISSN 1092-5783, Vol. 7, nr 7, s. 1-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In0.1Ga0.9N/In0.01Ga0.99N multiple quantum wells (MQWs) with heavily Si-doped barriers, grown with Metal Organic Vapor Phase Epitaxy (MOVPE) at about 800(0)C, have been studied in detail with optical spectroscopy. Such structures are shown to be very sensitive to a near surface depletion field, and if no additional layer is grown on top of the MQW structure the optical spectra from the individual QWs are expected to be drastically different. For a sample with 3 near surface QWs and Si-doped barriers, only the QW most distant from the surface is observed in photoluminescence (PL). The strong surface depletion field is suggested to explain these results, so that the QWs closer to the surface cannot hold the photo-excited carriers. A similar effect of the strong depletion field is found in an LED structure where the MQW is positioned at the highly doped n-side of the pn-junction. The internal polarization induced electric field in the QWs is also rather strong, and incompletely screened by carriers transferred from the doped barriers. The observed PL emission for this QW is of localized exciton character, consistent with the temperature dependence of peak position and PL decay time. The excitonic lineshape of 35-40 meV in the QW PL is explained as caused by a combination of random alloy fluctuations and interface roughness, the corresponding localization potentials are also responsible for the localization of the excitons in the low temperature range (

  • 183.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, JP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Kamiyama, S
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Iwaya, M
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Amano, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Akasaki, I
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Dept Elect Engn & Elect, Tempaku Ku, Nagoya, Aichi 468, Japan Meijo Univ, High Tech Res Ctr, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Photoluminescence of excitons in InxGa1-xN/InyGa1-yN multiple quantum wells2002Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 190, nr 1, s. 161-166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 184.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Iwaya, M
    Kamiyama, S
    Amano, H
    Akasaki, I
    A hydrogen-related shallow donor in GaN?2006Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, s. 460-463Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present photoluminescence (PL) data for deliberately O-doped, high-resistive GaN samples where a new shallow donor-bound exciton (DBE) peak at about 3.4746 eV (corrected for strain shift) at 2 K appears. This DBE is strongly enhanced upon annealing in the entire range 450-900 degrees C. The possible relation of this DBE to a metastable H donor state is discussed. (c) 2006 Elsevier B.V. All rights reserved.

  • 185.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Keller, S.
    DenBaars, S. P.
    Mishra, U. K.
    Effect of an (Al,In)N insertion layer on the radiative emission properties of (In,Ga)N/GaN multiple quantum well structures2007Ingår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 204, nr 1, s. 304-308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As an effort to investigate new techniques to reduce the effect of the strong internal polarization fields in (In,Ga)N/GaN quantum well (QW) structures we have studied the influence of inserting a thin wide band-gap AI(0 95)In(0.05)N interlayer inside the QWs, in order to modify the potential and increase the electron-hole overlap. A strong reduction of the decay times of the photoluminescence (PL) was observed in this case at all temperatures up to 300 K, without a strong reduction in PL intensity. The tunneling electron-hole transition across the interlayer is observed to be dominant at room temperature for high excitation conditions. (c) 2007 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.

  • 186.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Figge, S
    Dennemarck, J
    Hommel, D
    The dominant shallow 0.225 eV acceptor in GaN2006Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, nr 7, s. 1604-1608Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 187.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Hemmingsson, Carl
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Malinauskas, T
    Jarasiunas, K
    Gibart, P
    Beaumont, B
    Time-resolved spectroscopy of excitons bound at shallow neutral donors in HVPE GaN2006Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, s. 482-485Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 188.
    Monemar, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Paskov, Plamen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Bergman, Peder
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Pozina, Galia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Toropov, A.A.
    A. F. Ioffe Physico-Technical Institute, St. Petersburg, Russia.
    Shubina, T.V.
    A. F. Ioffe Physico-Technical Institute, St. Petersburg, Russia.
    Malinauskas, T.
    Institute of Materials Science and Applied Research, Vilnius University, Vilnius, Lithuania.
    Usui, A.
    R&D Division, Furukawa Co., Ltd., Tsukuba, Ibaraki, Japan.
    Transient photoluminescence of shallow donor bound excitons in GaN2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, s. 235202-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a detailed study of photoluminescence transients for neutral donor bound excitons (DBEs) in GaN, notably the ON donor DBE at 3.4714 eV and the SiGa DBE at 3.4723 eV. The studied samples are thick strain free nominally undoped bulk GaN samples, with a spectroscopic linewidth <0.5 meV at 2 K. The photoluminescence (PL) decay curves for these no-phonon (NP) lines are strongly nonexponential, and do not allow a proper assessment of the characteristic BE decay time. The decay of the LO-phonon replicas as well as the so-called two-electron transitions (TETs) at lower energies show a nicely exponential behavior, and allow extraction of DBE decay times of about 1.1 ns for the Si DBE and 1.8 ns for the O DBE, respectively. The initial nonexponential decay behavior of the NP lines has been studied in both the common front surface excitation-detection mode and with detection in transmission through the sample. This initial decay is explained as related to scattering processes in the near surface region, involving the DBEs and free excitons (FEs). Light scattering processes may also contribute to this complex decay shape. The DBE-LO-phonon decay does not discriminate between the O and Si DBEs because of spectral overlap involving different LO modes. The TET decays at 2 K are very different for transitions related to the DBE ground state and DBE excited states (going to p-like donor final states), for T>10 K thermalization between the DBE ground state and DBE excited states produces a common decay time. Thermalization between free and bound excitons appears to occur above about 20 K, when the DBE decay follows the FE decay. A simple two-level modeling of exciton capture and recombination for the PL decay curves of the FE and the DBEs, as commonly used in the literature, is shown to be generally inadequate. A broad PL background in the TET spectral region is suggested to be related to a radiative Auger process, where the DBEs recombine while leaving the donors ionized.

  • 189.
    Monemar, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Paskov, Plamen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Bergman, Peder
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Toropov, A.A.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021, Russian Federation.
    Shubina, T.V.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021, Russian Federation.
    Recent developments in the III-nitride materials2007Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 244, nr 6, s. 1759-1768Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We review a selection of recent research work on III-nitride materials, limiting the scope to bulk properties and quantum well structures. The different stages of development of the compounds AlN, GaN and InN are illustrated, with reference to the electronic properties demonstrated so far. The important alloy systems AlxGa1-xN and InxGa1-x have quite different properties, still not understood in detail for high Al and In contents, respectively. Some important unresolved issues are highlighted, and possible future directions of the materials development are indicated. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

  • 190.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Toropov, A.A.
    Shubina, T.V.
    Figge, S.
    Paskova, T.
    Hommel, D.
    Usui, A.
    Iwaya, M.
    Kamiyama, S.
    Amano, H.
    Akasaki, I.
    Optical signatures of dopants in GaN2006Ingår i: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 9, nr 1-3, s. 168-174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The characteristic optical spectra for shallow donors and acceptors in GaN are discussed. The most accurate photoluminescence (PL) data are obtained from samples grown on freestanding GaN substrates, where strain shifts are absent and a low spectroscopic line width is obtained. Recent PL data for excitons bound to the O and Si donors are discussed in some detail, giving accurate values for the binding energies and excited bound donor states. The Mg-acceptor is the most important one for p-doping, but the related optical spectra are controversial. We show that there are two acceptors present in Mg-doped GaN, with two different acceptor bound exciton peaks, and also two corresponding lower energy donor-acceptor pair spectra. We give tentative evidence for their interpretation. © 2006 Elsevier Ltd. All rights reserved.

  • 191.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Toropov, A.A.
    Shubina, T.V.
    Malinauskas, T.
    Usui, A.
    Recombination of free and bound excitons in GaN2008Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 245, nr 9, s. 1723-1740Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on recent optical investigations of free and bound exciton properties in bulk GaN. In order to obtain reliable data it is important to use low defect density samples of low doping. We have used thick GaN layers (of the order of 1 mm) grown by halide vapour phase epitaxy (HVPE) with a residual doping down to <1016 cm-3 in this work. With such samples all polarisation geometries could also easily be exploited. The influence of the surface states on the photoluminescence (PL) experiments is analysed, it is concluded that surface recombination plays an important role for the free exciton (FE) recombination. The electronic structure of the FEs is discussed in detail, including the influence of spin-exchange and polariton effects, and compared with polarised PL spectra at 2 K. The detailed structure of excited states from the PL spectra is discussed, but further data are needed to fully explain all the peaks observed. The polarized FE spectra at room temperature allow a determination of the bandgap as 3.437 eV at 290 K, assuming an exciton binding energy of 25 meV. The PL transient of the A FE is very short (about 100 ps) for the no-phonon (NP) line interpreted as dominated by nonradiative surface recombination. The longitudinal-optical (LO) phonon replicas of the A FE exhibit a longer decay of about 1.4 ns at 2 K, suggested to represent the bulk lifetime of the FE. The corresponding decay time at 290 K is 9 ns in our samples, a value that might be affected by nonradiative recombination. The Si and O donor bound exciton (DBE) spectra with sharp NP lines at 3.4723 eV and 3.4714 eV respectively, are well resolved together with the so-called two-electron transitions (TETs) and several optical phonon replicas. The electronic structure of the DBE states including excited rotational states is discussed and compared with experiment. The well-resolved TET lines allow an accurate determination of the ground state binding energy of the Si donor as 30.4 meV and 33.2 meV for the O donor. The PL transients of the DBEs reveal a non-exponential decay for the NP lines. The DBE NP transient lineshape is assumed to be influenced by optical dispersion and scattering in the vicinity of exciton resonances, as well as by surface effects. The DBE decay time can most properly be deduced from the PL decay of the respective TETs and LO replicas, leading to values in the range of 1.1-1.8 ns. These values differ significantly from previous theoretical predictions, where values about two orders of magnitude shorter were obtained. A tentative discussion of the main observed features of acceptor bound excitons (ABEs), which are much less studied in GaN, is given. A decay time of about 0.9 ns for the shallowest 3.466 eV ABE is estimated, i.e. shorter than that for the shallow donor BEs. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

  • 192.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Toropov, A.A.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St Petersburg, 194021, Russian Federation.
    Shubina, T.V.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St Petersburg, 194021, Russian Federation.
    Usui, A.
    R and D Division, Furukawa Co Ltd, Tsukuba, Ibaraki, 305-0856, Japan.
    Recombination dynamics of free and bound excitons in bulk GaN2008Ingår i: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 43, nr 5-6, s. 610-614Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report new data on the transient photoluminescence behaviour of free and donor bound excitons in high quality bulk GaN material grown by HVPE. With 266 nm photoexcitation the no-phonon free exciton has a short decay time, about 100 ps at 2 K, assigned to nonradiative surface recombination. The LO replicas of the free exciton have a much longer decay at 2 K, about 1.4 ns, believed to be a lower bound for the bulk radiative lifetimes of the free excitons at 2 K. The donor bound exciton no-phonon lines exhibit a rather short (about 300 ps) nonexponential decay at 2 K, which appears to be dominated by a scattering process. The corresponding LO replicas and the two-electron transitions have a much longer decay. From the latter, the lower bound of the radiative lifetime of the O- and Si-bound excitons are 1800 ps and 1100 ps, respectively. © 2007 Elsevier Ltd. All rights reserved.

  • 193.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Haradizadeh, H
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Valcheva, E
    Darakchieva, Vanya
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Arnaudov, B
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Holtz, Per-Olof
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Kamiyama, S
    Iwaya, M
    Amano, H
    Akasaki, I
    Optical investigation of AlGaN/GaN quantum wells and superlattices2004Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 201, nr 10, s. 2251-2258Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 194.
    Monemar, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Paskov, Plamen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Haratizadeh, H.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Holtz, Per-Olof
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Bergman, Peder
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
    Kamiyama, S.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Iwaya, M.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Amano, H.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Akasaki, I.
    Dept. of Materials Science and Eng., Hi Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 468, Japan.
    Photoluminescence of InGaN/GaN and AlGaN/GaN multiple quantum well structures: Role of depletion fields and polarization fields2003Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 195, nr 3, s. 523-527Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 195.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Haratizadeh, H.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Kamiyama, S.
    Department of Electrical Engineering, Electron./High-Tech. Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Iwaya, M.
    Department of Electrical Engineering, Electron./High-Tech. Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Amano, H.
    Department of Electrical Engineering, Electron./High-Tech. Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Akasaki, I.
    Department of Electrical Engineering, Electron./High-Tech. Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Optical properties of InGaN/GaN and AlGaN/GaN multiple quantum well structures2003Ingår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 5023, s. 63-67Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We report on low temperature photoluminescence (PL) in In xGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si doped barriers of In0.01Ga0.99N. One sample with 3 QWs of width 3.5 nm and barriers of width 10.5 nm had the MQW in the depletion region of the outer surface. Two PL peaks were observed, one QW exciton from the QW closest to the GaN buffer, one lower energy peak related to a 2DEG at the interface to the GaN buffer layer. In a second similar sample 5 QWs of width 3 nm and with 6 nm highly Si doped In0.01Ga 0.99N barriers the MQW was placed in the n-side depletion region of a pn-junction. At low temperatures the PL and electroluminescence (EL) spectra are quite different at no, low, or reverse bias, the PL appearing at higher energy. At high forward bias a spectral component at the EL position appears. This proves a strong influence of the depletion field on the optical spectra. Preliminary results are also reported for n-doped Al0.07Ga 0.93N/GaN structures, with near surface MQWs.

  • 196.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Paskov, Plamen
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Kasic, A.
    Optical properties of InN - The bandgap question2005Ingår i: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 38, nr 1, s. 38-56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The bandgap value of InN was analyzed, with reference to optical data on single crystalline thin films samples grown on sapphire. It was found that the line shape of the photoluminescence spectra could be quite well reproduced in a model for the optical transitions from the conduction band states to localized states above the valence band. It was also found that the conduction band transition requires the presence of deep donor at a concentration close to 1020 cm∓3. The results show that the bandgap of pure InN should be about 0.69 eV at 2 K.

  • 197.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Chen, Weimin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Hai, P.N.
    Hai, P.N..
    Buyanova, Irina A.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Amano, H.
    Department of Materials Science and Engineering, High Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Akasaki, I.
    Department of Materials Science and Engineering, High Tech Research Center, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468, Japan.
    Optical characterization of III-nitrides2002Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 198.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, JP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Kamiyama, S
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Iwaya, M
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Amano, H
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Akasaki, I
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Meijo Univ, Hi Tech Res Ctr, Dept Mat Sci & Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Influence of depletion fields on photoluminescence of n-doped InGaN/GaN multiple quantum well structures2002Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 192, nr 1, s. 21-26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 199.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Hemmingsson, Carl
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Kawashima, T.
    Amano, H.
    Akasaki, I.
    Usui, A.
    Optical properties and acceptor states in Mg doped GaN2008Ingår i: 8^th Akasaki Symposium,2008, 2008Konferensbidrag (Övrigt vetenskapligt)
  • 200.
    Monemar, Bo
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Paskov, Plamen
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Pozina, Galia
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Bergman, Peder
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Hemmingsson, Carl
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Materiefysik.
    Toropov, A.A.
    Choubina, Tatiana
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Kawashima, T.
    Amano, H.
    Akasaki, I.
    Usui, A.
    Paskova, Tanja
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
    Properties of dopants and defects in GaN from bound exciton spectra2008Ingår i: Meijo International Symposium on Nitride Semiconductors 2008,2008, 2008Konferensbidrag (Övrigt vetenskapligt)
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