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  • 1.
    Ail, Ujwala
    et al.
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Nilsson, Jakob
    Ligna Energy AB, Sweden.
    Jansson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Wu, Zhixing
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Björk, Emma
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Berggren, Magnus
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Crispin, Xavier
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Optimization of Non-Pyrolyzed Lignin Electrodes for Sustainable Batteries2023In: ADVANCED SUSTAINABLE SYSTEMS, ISSN 2366-7486, Vol. 7, no 2, article id 2200396Article in journal (Refereed)
    Abstract [en]

    Lignin, a byproduct from the pulp industry, is one of the redox active biopolymers being investigated as a component in the electrodes for sustainable energy storage applications. Due to its insulating nature, it needs to be combined with a conductor such as carbon or conducting polymer for efficient charge storage. Here, the lignin/carbon composite electrodes manufactured via mechanical milling (ball milling) are reported. The composite formation, correlation between performance and morphology is studied by comparison with manual mixing and jet milling. Superior charge storage capacity with approximate to 70% of the total contribution from the Faradaic process involving the redox functionality of lignin is observed in a mechanically milled composite. In comparison, manual mix shows only approximate to 30% from the lignin storage participation while the rest is due to the electric double layer at the carbon-electrolyte interface. The significant participation of lignin in the ball milled composite is attributed to the homogeneous, intimate mixing of the carbon and the lignin leading the electronic carrier transported in the carbon phase to reach most of the redox group of lignin. A maximum capacity of 49 mAh g(-1) is obtained at charge/discharge rate of 0.25 A g(-1) for the sample milled for 60 min.

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  • 2.
    Balagula, Roman
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Jansson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Yukimune, Mitsuki
    Ehime Univ, Japan.
    Stehr, Jan Eric
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ishikawa, Fumitaro
    Ehime Univ, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Effects of thermal annealing on localization and strain in core/multishell GaAs/GaNAs/GaAs nanowires2020In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, no 1Article in journal (Refereed)
    Abstract [en]

    Core/shell nanowire (NW) heterostructures based on III-V semiconductors and related alloys are attractive for optoelectronic and photonic applications owing to the ability to modify their electronic structure via bandgap and strain engineering. Post-growth thermal annealing of such NWs is often involved during device fabrication and can also be used to improve their optical and transport properties. However, effects of such annealing on alloy disorder and strain in core/shell NWs are not fully understood. In this work we investigate these effects in novel core/shell/shell GaAs/GaNAs/GaAs NWs grown by molecular beam epitaxy on (111) Si substrates. By employing polarization-resolved photoluminescence measurements, we show that annealing (i) improves overall alloy uniformity due to suppressed long-range fluctuations in the N composition; (ii) reduces local strain within N clusters acting as quantum dot emitters; and (iii) leads to partial relaxation of the global strain caused by the lattice mismatch between GaNAs and GaAs. Our results, therefore, underline applicability of such treatment for improving optical quality of NWs from highly-mismatched alloys. They also call for caution when using ex-situ annealing in strain-engineered NW heterostructures.

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  • 3.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S.
    Department of Electrical and Computer Engineering, University of California, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Strong room-temperature optical and spin polarization in InAs/GaAs quantum dot structures2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 20, p. 203110-Article in journal (Refereed)
    Abstract [en]

    Room-temperature optical and spin polarization up to 35% is reported in InAs/GaAs quantum dots in zero magnetic field under optical spin injection using continuous-wave optical orientation spectroscopy. The observed strong spin polarization is suggested to be facilitated by a shortened trion lifetime, which constrains electron spin relaxation. Our finding provides experimental demonstration of the highly anticipated capability of semiconductor quantum dots as highly polarized spin/light sources and efficient spin detectors, with efficiency greater than 35% in the studied quantum dots.

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  • 4.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, Suwaree
    UC San Diego, USA.
    Tu, Charles
    UC San Diego, USA.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Spin injection in lateral InAs quantum dot structures by optical orientation spectroscopy2009In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 20, no 37, p. 375401-Article in journal (Refereed)
    Abstract [en]

    Optical spin injection is studied in novel laterally-arranged self-assembled InAs/GaAs quantum dot structures, by using optical orientation measurements in combination with tunable laser spectroscopy. It is shown that spins of uncorrelated free carriers are better conserved during the spin injection than the spins of correlated electrons and holes in an exciton. This is attributed to efficient spin relaxation promoted by the electron–hole exchange interaction of the excitons. Our finding suggests that separate carrier injection, such as that employed in electrical spin injection devices, can be advantageous for spin conserving injection. It is also found that the spin injection efficiency decreases for free carriers with high momentum, due to the acceleration of spin relaxation processes.

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  • 5.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, Suwaree
    Dept of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA.
    Tu, Charles W
    Dept of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Efficiency of spin injection in novel InAs quantum dotstructures: exciton vs. free carrier injection2010Conference paper (Refereed)
    Abstract [en]

    Unambiguous experimental evidence for a significant difference in efficiency of excitonic vs. free carrier spin injection is provided in novel laterally arranged self-assembled InAs/GaAs quantum dot structures, from optical orientation and tunable laser spectroscopy. A lower efficiency of exciton spin injection as compared to free carrier spin injection from wetting layers into QDs results in a distinct feature in luminescence polarization of the QDs as a function of excitation photon energy. It is shown that this difference is not related to carrier density and state-filling effects arising from the difference in optical absorption efficiency between the excitons and free carriers. Rather, it is a genuine property for exciton spin injection that suffers stronger spin relaxation due to Coulomb exchange interaction.

  • 6.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Sernelius, Bo E.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Strong suppression of spin generation at a Fano resonance in a semiconductor nanostructure2012Manuscript (preprint) (Other academic)
    Abstract [en]

    We observe remarkable, complete suppression of spin generation under optical excitation in a thin InAs/GaAs wetting layer close to the light-hole excitonic resonance, leading to zero electron spin polarization as monitored by adjacent InAs quantum dots. The suppression is attributed to efficient spin relaxation/scattering at the Fano resonance between the light-hole exciton states and the heavy-hole continuum of the wetting layer. The complete suppression is found to remain effective up to temperatures exceeding 100 K.

  • 7.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    n/a.
    Tu, C W
    n/a.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Efficiency of spin injection in novel InAs quantum dots structures2009In: Abstract Book of the 14th International Conference on Modulated Semiconductor structures (MSS-14), Kobe, Japan, July 19 - 24, 2009, 2009, p. 164-Conference paper (Other academic)
  • 8.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Hanle effect and electron spin polarization in InAs/GaAs quantum dots up to room temperature2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 13, p. 135705-Article in journal (Refereed)
    Abstract [en]

    Hanle effect in InAs/GaAs quantum dots (QDs) is studied under optical orientation as a function of temperature over the range of 150-300 K, with the aim to understand the physical mechanism responsible for the observed sharp increase of electron spin polarization with increasing temperature. The deduced spin lifetime Ts of positive trions in the QDs is found to be independent of temperature, and is also insensitive to excitation energy and density. It is argued that the measured Ts is mainly determined by the longitudinal spin flip time (T1) and the spin dephasing time (T2 *) of the studied QD ensemble, of which both are temperatureindependent over the studied temperature range and the latter makes a larger contribution. The observed sharply rising of the QD spin polarization degree with increasing temperature, on the other hand, is shown to be induced by an increase in spin injection efficiency from the barrier/wetting layer and also by a moderate increase in spin detection efficiency of the QD.

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  • 9.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Hanle effect in InAs/GaAs quantum dots up to room temperatures2011In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528Article in journal (Refereed)
  • 10.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    InAs/GaAs quantum dots as highly polarized spin and light sources and efficient spin detectors at room temperature.2012Conference paper (Other academic)
  • 11.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Optical spin injection and spin detection in novel InAs quantum dot structures.2011In: Abstract book of the SPIE Microtechnologies, 2011, p. 8068B-51-Conference paper (Other academic)
  • 12.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, Suwaree
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA.
    Tu, Charles
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Free-carriers beat excitons in spin-injection contest2009Other (Other (popular science, discussion, etc.))
    Abstract [en]

    Quantum dots (QDs) are a promising building block for future spin-functional devices with applications in spintronics and quantum information processing. Essential to the success of these devices is the ability to create a desired spin orientation of charge carriers (electrons and holes) in QDs via the injection of spin-polarized carriers. Researchers have now shown that this can be done most efficiently using independent (free) carriers rather than electron-hole pairs (excitons).

  • 13.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Hyperfine-induced spin depolarization and dynamic nuclear polarization in InAs/GaAs quantum dots2012Conference paper (Other academic)
  • 14.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California 92093, USA.
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Temperature dependence of dynamic nuclear polarization and its effect on electron spin relaxation and dephasing in InAs/GaAs quantum dots2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 14, p. 143105-Article in journal (Refereed)
    Abstract [en]

    Electron spin dephasing and relaxation due to hyperfine interaction with nuclear spins is studied in an InAs/GaAs quantum dot ensemble as a function of temperature up to 85 K, in an applied longitudinal magnetic field. The extent of hyperfineinduced dephasing is found to decrease, whereas dynamic nuclear polarization increases with increasing temperature. We attribute both effects to an accelerating electron spin relaxation through phonon-assisted electron-nuclear spin flip-flops driven by hyperfine interactions, which could become the dominating contribution to electron spin depolarization at high temperatures.

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  • 15.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, P. H.
    Suraprapapich, S.
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Spin properties in InAs/GaAs quantum dot structures: Invited talk at the Second Int. Conf. on Small Science (ICSS 2012), Orlando, USA, Dec.16-19 2012.2012Conference paper (Other academic)
  • 16.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, P. H.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S.
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Effect of in-plane anisotropy on spin injection efficiency in InAs/GaAs nanostructures revealed in a longitudinal magnetic field2012Conference paper (Other academic)
  • 17.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, P. H.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Effects of a longitudinal magnetic field on spin injection and detection in InAs/GaAs quantum dot structures2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 14, p. 145304-Article in journal (Refereed)
    Abstract [en]

    Effects of a longitudinal magnetic field on optical spin injection and detection in InAs/GaAs quantum dot (QD) structures are investigated by optical orientation spectroscopy. An increase in optical and spin polarization of the QDs is observed with increasing magnetic field in the range of 0-2 T, and is attributed to suppression of exciton spin depolarization within the QDs that is promoted by hyperfine interaction and anisotropic electron-hole exchange interaction. This leads to a corresponding enhancement in spin detection efficiency of the QDs by a factor of up to 2.5. At higher magnetic fields when these spin depolarization processes are quenched, electron spin polarization in anisotropic QD structures (such as double QDs that are preferably aligned along a specific crystallographic axis) still exhibits rather strong field dependence under non-resonant excitation. In contrast, such field dependence is practically absent in more "isotropic" QD structures (e.g. single QDs). We attribute the observed effect to stronger electron spin relaxation in the spin injectors (i.e. wetting layer and GaAs barriers) of the lower-symmetry QD structures, which also explains the lower spin injection efficiency observed in these structures.

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  • 18.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, Po-Hsiang
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S.
    University of California, USA.
    Tu, C. W.
    University of California, USA.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Quantum dot structures: limiting factors for spintronics2012Other (Other (popular science, discussion, etc.))
    Abstract [en]

    Rich information on the dominant factors limiting spin injection and detection efficiency can be retrieved from optical orientation in a longitudinal magnetic field.

  • 19.
    Bian, Qingzhen
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ma, Fei
    Division of Chemical Physics, Lund University, Lund, Sweden.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Wei, Qi
    Institute of Applied Physics and Materials Engineering, University of Macau, Macau SAR, China.
    Su, Xiaojun
    Division of Chemical Physics, Lund University, Lund, Sweden.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ponseca, Carlito S.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Linares, Mathieu
    Department of Theoretical Chemistry and Biology, KTH Royal Institute of Technology, Stockholm, Sweden.
    Karki, Khadga J.
    Division of Chemical Physics, Lund University, 22100, Lund, Sweden.
    Yartsev, Arkady
    Division of Chemical Physics, Lund University, Lund, Sweden.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes2020In: Nature Communications, E-ISSN 2041-1723, Vol. 11, no 1, article id 617Article in journal (Refereed)
    Abstract [en]

    Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial ~200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications.

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  • 20.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Magnetic Resonance Studies of Oxygen and Zinc-Vacancy Native Defects in Bulk ZnO Crystals2010In: Bulletin of the American Physical Society, 2010, p. A25.00001-Conference paper (Other academic)
    Abstract [en]

    ZnO is currently attracting increasing attention as a key material for a wide variety of electronic and optoelectronic applications. Optical, electrical, and magnetic properties of ZnO are believed to be strongly influenced by native defects. However, unambiguous experimental evidence confirming the formation of these defects in as-grown ZnO as well as evaluations of defect densities is currently sparse. In this talk we shall review our recent results from comprehensive defect characterization of as-grown bulk ZnO. By using electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) spectroscopies, we show that both oxygen and zinc vacancies are formed in ZnO grown from melt without subjecting to irradiation. Defect concentrations are also determined. Based on spectral dependences of its EPR and ODMR signals, the VZn- defect is concluded to act as a deep acceptor responsible for the red emission peaking at around 1.6 eV, but does not participate in the green emission as commonly believed. The energy level position of the VZn corresponding to the (2-/-) transition is determined to be at Ev+1.0 eV. The center is also shown to exhibit a strong JT distortion with a JT energy of 0.8 eV. On the other hand, oxygen vacancies are probably less important in carrier recombination since they were only detected in EPR but not in ODMR. Annealing properties of both defects were also studied and higher thermal stability of the Zn vacancy was concluded. It was also suggested that annealing of the VZn centers is facilitated by thermally-activated diffusion of impurity atoms to the VZn sites. The obtained results are of importance for a better understanding of the defects in ZnO. They also provide useful information on control of electrical properties and defect-reaction induced degradation during device processing and operation, in the material that is commonly used as a substrate for epitaxial growth of layered device structures based on ZnO.

  • 21.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Identification of the Dominant Recombination Centers in Dilute Nitrides2010In: Abstract book, EM-TuA3, 2010, p. 72-Conference paper (Other academic)
  • 22.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Photon upconversion promoted by defects in low-dimensional semiconductor nanostructures2018In: Defects in Advanced Electronic Materials and Novel Low Dimensional Structures / [ed] Jan Stehr, Irina Buyanova and Weimin Chen, UK: Elsevier, 2018, p. 189-210Chapter in book (Refereed)
    Abstract [en]

    The ability to convert several low-energy photons into a single higher-energy photon is of significant importance in diverse fields ranging from imaging and biological labeling to optoelectronics and photovoltaics. The possibility to realize this phenomenon on the nanoscale can provide an additional degree of freedom in engineering electronic properties of materials and would allow deliberate manipulation and optimization of the upconversion processes. The purpose of this chapter is to provide a review of physical mechanisms that govern the photon upconversion in semiconductor nanostructures. Taking into account a large number of comprehensive reviews on this topic, our main focus is on photon upconversion mediated by defects, which is far less explored so far but provides a viable and attractive alternative for achieving efficient photon upconversion without involving doping.

  • 23.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Vacancy-related defects in ZnO2010In: Abstract book of the AVS International Symposium and Exhibition, Albuquerque, USA, October 17-22, 2010, 2010, p. 72-Conference paper (Other academic)
  • 24.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Goldys, E.M.
    Division of Information and Communication Sciences, Macquarie University, Sydney, NSW, Australia.
    Phillips, M.R.
    Microstructural Analysis Unit, University of Technology, Sydney, NSW, Australia.
    Xin, H.P.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA, United States.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA, United States.
    Strain relaxation in GaNxP1-x alloy: Effect on optical properties2001In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 308-310, p. 106-109Article in journal (Refereed)
    Abstract [en]

    By using scanning electron microscopy and cathodoluminescence (CL), a decrease in radiative efficiency of GaNP alloy with increasing N content is seen due to the formation of structural defects. The defect formation is attributed to relaxation of tensile strain in the GaNP layer, which is lattice mismatched to GaP substrate. Several types of extended defects including dislocations, microcracks and pits are revealed in partly relaxed GaNxP1-x epilayers with x=1.9%, whereas coherently strained layers exhibit high crystalline quality for x up to 4%. According to the CL measurements, all extended defects act as competing, non-radiative channels leading to the observed strong decrease in the radiative efficiency. From CL mapping experiments, non-uniformity of strain distribution around the extended defects is partly responsible for the broadening of the photoluminescence (PL) spectra recorded in the macro-PL experiments. © 2001 Elsevier Science B.V. All rights reserved.

  • 25.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Oka, Y.
    Abernathy, C. R.
    Pearton, S. J.
    Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures2007In: 2006 E-MRS Fall Meeting, 2007, Vol. 204, no 1, p. 159-173Conference paper (Refereed)
    Abstract [en]

    In this paper we review our recent results from in-depth investigations of physical mechanisms which govern efficiency of several processes important for future spintronic devises, such as spin alignment within diluted magnetic semiconductors (DMS), spin injection from DMS to non-magnetic spin detectors (SDs) and also spin depolarization within SD. Spin-injection structures based on II-VIs (e.g. ZnMnSe/Zn(Cd)Se) and III-Vs (e.g. GaMnN/Ga(In)N) were studied as model cases. Exciton spin relaxation within ZnMnSe DMS, important for spin alignment, was found to critically depend on Zeeman splitting of the exciton states and is largely facilitated by involvement of longitudinal optical (LO) phonons. Optical spin injection in ZnMnSe/Zn(Cd)Se was shown to be governed by (i) commonly believed tunneling of individual carriers or excitons and (ii) energy transfer via localized excitons and spatially separated localized electron-hole pairs (LEHP) located within DMS. Unexpectedly, the latter mechanism is in fact found to dominate spin injections. We shall also show that spin depolarization in the studied structures is essentially determined by efficient spin relaxation within non-magnetic spin detectors, which is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.

  • 26.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hai, P.N.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Xin, H.P.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093-0407, United States.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093-0407, United States.
    Optical properties of GaNAs/GaAs structures2001In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 82, no 1-3, p. 143-147Article in journal (Refereed)
    Abstract [en]

    We review our recent results on optical characterization of MBE-grown GaNAs/GaAs quantum structures with N content up to 4.5%, by employing photoluminescence (PL), PL excitation, and time-resolved PL spectroscopies. The dominant PL mechanism has been determined as recombination of excitons trapped by potential fluctuations of the band edge, due to composition disorder and strain nonuniformity of the alloy. The estimated value of the localization potential is around 60 meV for the low-temperature grown structures and can be reduced by increasing the growth temperature or using post-growth rapid thermal annealing (RTA). © 2001 Elsevier Science S.A.

  • 27.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Tu, C. W.
    Univ Calif, Dept Elect & Comp Engn, La Jolla, CA USA.
    Optical and electronic properties of GaInNP alloys - a new material system for lattice matching to GaAs2008In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 205, no 1, p. 101-106Article in journal (Refereed)
    Abstract [en]

    In this paper we will review our recent results from optical characterization studies of GaInNP. We will show that N incorporation in these alloys affects their structural and defect properties, as well as the electronic structure. The main structural changes include (i) increasing carrier localization due to strong compositional fluctuations, which is typical for all dilute nitrides, and (ii) N-induced long range ordering effects, specific for GaInNP. The observed degradation of radiative efficiency of the alloys upon increasing N content is attributed to formation of several defects acting as centres of efficient non-radiative recombination. One of the defects is identified as a complex involving a Ga interstitial atom. N incorporation is also found to change the band line up from the type I in the GaInP/GaAs structures to the type 11 in the GaInNP/GaAs heterojunctions with [N] > 0.5%. For the range of N compositions studied ([N] <= 2%), a conduction band offset at the GaInNP/GaAs interface is found to nearly linearly depend on [N] at -0.10 eV/%, whereas the valence band offset remains unaffected. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 28.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Hallberg, T
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Swedish Def Res Estab, S-58111 Linkoping, Sweden Inst Solid State & Semicond Phys, Minsk 220072, Byelarus Univ Lund, S-22100 Lund, Sweden.
    Murin, LI
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Swedish Def Res Estab, S-58111 Linkoping, Sweden Inst Solid State & Semicond Phys, Minsk 220072, Byelarus Univ Lund, S-22100 Lund, Sweden.
    Markevich, VP
    Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Swedish Def Res Estab, S-58111 Linkoping, Sweden Inst Solid State & Semicond Phys, Minsk 220072, Byelarus Univ Lund, S-22100 Lund, Sweden.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lindstrom, JL
    Effect of high-temperature electron irradiation on the formation of radiative defects in silicon1999In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 274, p. 528-531Article in journal (Refereed)
    Abstract [en]

    Defect formation processes in silicon caused by electron irradiation performed at elevated temperatures are studied in detail using photoluminescence (PL) spectroscopy. The use of high temperature during electron irradiation has been found to affect considerably the defect formation process, In particular, several new unknown excitonic PL lines were discovered in carbon-rich Si wafers subjected to electron irradiation at temperatures higher than 450 degrees C, The dominant new luminescent center gives rise to a bound exciton PL emission at 0.961 eV. The center is shown to be efficiently created by electron irradiation at temperatures from 450 degrees C up to 600 degrees C. The electronic structure of the 0.961 eV PL center can be described as a pseudodonor case, where the hole is strongly bound at a level 187 meV above the valence band, while the electron is a effective-mass-like particle weakly bound by approximate to 21 meV in the BE state, (C) 1999 Elsevier Science B.V. All rights reserved.

  • 29.
    Buyanova, Irina A
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials.
    Ishikawa, Fumitaro
    Ehime university, Japan.
    Chen, Weimin
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials.
    GaNAs-based nanowires for near-infrared optoelectronics2018In: Novel compound semiconductor nanowires: materials, devices, and applications / [ed] Irina A. Buyanova, Fumutaro Ishikawa, Singapore: Pan Stanford Publishing, 2018, Vol. Sidorna 133-159, p. 133-159Chapter in book (Other academic)
    Abstract [en]

    This chapter analyses the impacts of alloying with nitrogen on structural properties and recombination processes in GaNAs nanowires (NW). It discusses possible innovative applications of these structures in advanced nano-emitters, where the incorporation of nitrogen induces the formation of self-assembled quantum dot-like states embedded in the NWs. The structural properties of these NWs were investigated by transmission electron microcopy. An important material parameter that affects performance of the NW-based devices is carrier lifetime. The non-radiative lifetime is largely affected by the material quality both in bulk and within near-surface regions. The contribution of the surface-related recombination is known to be especially severe in GaAs-based NW structures due to a large surface-to-volume ratio and the presence of surface states participating in the non-radiative recombination processes. The revealed optical properties of the GaNAs-based NW structures may be attractive for future optoelectronic applications in advanced nano-sized light emitters which could be integrated with silicon technology.

  • 30.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Izadifard, Morteza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Seppänen, Timo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Pearton, SJ
    Polimeni, A
    Capizzi, M
    Brandt, MS
    Bihler, C
    Hong, YG
    Tu, CW
    Unusual effects of hydrogen on electronic and lattice properties of GaNP alloys2006In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, p. 568-570Article in journal (Refereed)
    Abstract [en]

    Hydrogen incorporation is shown to cause passivation of various N-related localized states and partial neutralization of N-induced changes in the electronic structure of the GaNxP1-x alloys with x < 0.008. According to the performed X-ray diffraction measurements, the hydrogenation is also found to cause strong expansion of the GaNP lattice which even changes from a tensile strain in the as-grown GaNP epilayers to a compressive strain in the post-hydrogenated structures with the highest H concentration. By comparing results obtained using two types of hydrogen treatments, i.e. by implantation from a Kaufman source and by using a remote dc H plasma, the observed changes are shown to be inherent to H due to its efficient complexing with N atoms, whereas possible effects of implantation damage are only marginal. (c) 2005 Elsevier B.V. All rights reserved.

  • 31.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lindstrom, J.L.
    Lindström, J.L., Solid State Physics, Univ. of Lund, Box 118, S-221 00, Lund, Sweden.
    Hallberg, T.
    Murin, L.I.
    Inst. Solid Stt. Semiconduct. Phys., 220072, Minsk, Belarus.
    Markevich, V.P.
    Inst. Solid Stt. Semiconduct. Phys., 220072, Minsk, Belarus.
    Photoluminescence characterization of defects created in electron-irradiated silicon at elevated temperatures2000In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 72, no 2, p. 146-149Article in journal (Refereed)
    Abstract [en]

    Photoluminescence (PL) spectroscopy is employed to investigate radiative defects created in Si during electron-irradiation at elevated temperatures. The use of high temperature during electron irradiation has been found to affect considerably the defect formation process. The effect critically depends on the temperature of the irradiation as well as doping of the samples. For carbon-lean Si wafers high temperature electron irradiation stimulates the formation of extended defects, such as dislocations and precipitates. For carbon-rich Si wafers the increase of irradiation temperature up to 300°C enhances the formation of the known carbon-related defects. In addition, several new excitonic PL lines were observed after electron irradiation at T = 450°C. The dominant new PL center gives rise to a BE PL emission at 0.961 eV. The electronic structure of the 0.961 eV defect is discussed based on temperature-dependent and magneto-optical studies.

  • 32.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Rudko, G.Yu.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Kayanuma, K.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
    Murayama, A.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
    Toropov, A.A.
    A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Sorokin, S.V.
    A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Ivanov, S.V.
    A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Effect of momentum relaxation on exciton spin dynamics in diluted magnetic semiconductor ZnMnSe CdSe superlattices2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 16Article in journal (Refereed)
    Abstract [en]

    cw hot photoluminescence (PL) complemented by transient PL measurements is employed to evaluate momentum and spin relaxation of heavy hole (HH) excitons in ZnMnSe CdSe superlattices. The rate of acoustic-phonon assisted momentum relaxation is concluded to be comparable to the total rate of exciton decay processes, about (2-3) × 1010 s-1, independent of applied magnetic fields. In magnetic fields when the Zeeman splitting ? of the exciton states is below the energy of the longitudinal optical (LO) phonon (?LO), a surprisingly strong suppression of spin relaxation rate from the bottom of the upper spin band is observed, which becomes comparable to that of momentum scattering via acoustic phonons. On the other hand, dramatic acceleration of the spin relaxation process by more than one order of magnitude is found for the excitons with a high momentum K. The findings are interpreted as being due to electron and hole spin flip processes via exchange interaction with isolated Mn2+ ions. Experimental evidence for the efficient interaction between the hot excitons and Mn impurities is also provided by the observation of spin flip transitions within Mn2+ - Mn2+ pairs that accompany the momentum relaxation of the hot HH excitons. In higher magnetic fields ?= ?LO, abrupt shortening of the spin flip time is observed. It indicates involvement of a new and more efficient spin relaxation process and is attributed to direct LO-assisted exciton spin relaxation with a subpicosecond spin relaxation time. © 2005 The American Physical Society.

  • 33.
    Buyanova, Irina A
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials.
    Tu, Charles W.
    University of California, LaJolla.
    Chen, Weimin
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials.
    Novel GaNP nanowires for advanced optoelectronics and photonics2018In: Novel compound semiconductor nanowires: materials, devices, and applications / [ed] Irina A. Buyanova, Fumitaro Ischikawa, Singapore: Pan Stanford Publishing, 2018, Vol. Sidorna 107-132, p. 107-132Chapter in book (Other academic)
    Abstract [en]

    This chapter discusses structural and optical properties of novel GaNP nanowires (NW), as well as their potential for future applications in optoelectronics and photonics. It reviews efforts devoted to the optimization of GaNP-based NWs for future applications in light-emitting devices and discusses the impacts of structural polymorphism on the radiative efficiency and band structure of the material. The chapter shows that GaNP NWs can be utilized as a source of linearly polarized light with the polarization direction that is not determined by dielectric mismatch between the NW and its surrounding. GaNP alloys are novel III–V semiconductors, which have a great potential for applications in amber-red light-emitting diodes and also as an active material in innovative intermediate the band solar cells. NWs grown under the non-optimized conditions usually suffer from various point and structural defects, which degrade the radiative efficiency.

  • 34.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Tu, Charles W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California, USA.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Novel GaNP Nanowires for Advanced Optoelectronics and Photonics2018In: Novel Compound Semiconductor Nanowires: Materials, Devices, and Applications / [ed] F. Ishikawa; I. A. Buyanova, Pan Stanford Publishing, 2018, p. 107-132Chapter in book (Other academic)
  • 35.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, Xingjun
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, W M
    University of California.
    Tu, C W
    University of California.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Effects of Ga doping on optical and structural properties of ZnO epilayers2009In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 45, no 4-5, p. 413-420Article in journal (Refereed)
    Abstract [en]

    Effects of Ga incorporation on electrical, structural and optical properties of ZnO epilayers are systematically studied by employing structural and optical characterization techniques combined with electrical and secondary ion mass spectrometry measurements. A non-monotonous dependence of free electron concentrations on Ga content is observed and is attributed to defect formation and phase separation. The former process is found to dominate for Ga concentrations of around 2-3x1020 cm-3. corresponding defects are suggested to be responsible for a broad red emission, which peaks at around 1.8 eV at K. Characteristic properties of this emission are well accounted for by assuming intracenter transitions at a deep center, of which the associated Huang-Rhys factor and mean phonon energy are determined. For higher Ga doping levels, the phase separation is found to be significant. It is that under these conditions only a minor fraction of incorporated Ga atoms form shallow donors, which leads to the observed dramatic decrease of carrier concentration.

  • 36.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Izadifard, Morteza
    Physics Department, Shahrood University of Technology, Shahrood, Iran .
    Hong, Y.G.
    Department of Electrical and Computer Engineering, University of California, La Jolla, CA, USA.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, CA, USA.
    Role of nitrogen in photoluminescence up-conversion in GaInNP/GaAs heterostructures2007In: AIP Conference Proceedings / Volume 893 / [ed] Wolfgang Jantsch, Friedrich Schaffler, American Institute of Physics (AIP), 2007, p. 381-382Conference paper (Other academic)
    Abstract [en]

    Alloying of disordered GaInP with nitrogen is shown to lead to very efficient PLU in GaInNP/GaAs heterostructures grown by gas source molecular beam epitaxy (GS‐MBE). This is attributed to the N‐induced changes in the band alignment at the GaInNP/GaAs heterointerface from the type I for the N‐free structure to the type II in the samples with N compositions exceeding 0.5%. Based on the performed excitation power dependent measurements, a possible mechanism for the energy upconversion is suggested as being due to the two‐step two‐photon absorption. The photon recycling effect is shown to be important for the structures with N=1%, from time‐resolved PL measurements. © 2007 American Institute of Physics

  • 37.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Thaler, G.
    Frazier, R.
    Abernathy, C. R.
    Pearton, S. J.
    Kim, J.
    Ren, F.
    Kyrychenko, F. V.
    Stanton, C. J.
    Pan, C.-C.
    Chen, G.-T.
    Chyi, J.-I.
    Zavada, J. M.
    Optical study of spin injection dynamics in InGaN/GaN quantum wells with GaMnN injection layers2004In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 22, no 6, p. 2668-2672Article in journal (Refereed)
    Abstract [en]

     The spin injection dynamics of GaMnN/InGaN multiquantum well (MQW) light emitting diodes (LEDs) grown by molecular beam epitaxy were examined using picosecond-transient and circularly polarized photoluminescence (PL) measurements. Even with the presence of a room temperature ferromagnetic GaMnN spin injector, the LEDs are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN MQW, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection. Typical photoluminescence decay times were 20-40 ns in both commercial GaN MQW LEDs with emission wavelengths between 420-470 nm and in the GaMnN/InGaN multi-quantum well MQW LEDs. In the wurtzite InGaN/GaN system, biaxial strain at the interfaces give rise to large piezoelectric fields directed along the growth axis. This built-in piezofield breaks the reflection symmetry of confining potential leading to the presence of a large Rashba term in the conduction band Hamiltonian which is responsible for the short spin relaxation times.

  • 38.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rawal, S.
    Norton, D.P.
    Pearton, S.J.
    Osinsky, A.
    Dong, J.W.
    Mechanism for radiative recombination in ZnCdO alloys2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 26Article in journal (Refereed)
    Abstract [en]

    Temperature dependent cw- and time-resolved photoluminescence combined with absorption measurements are employed to evaluate the origin of radiative recombination in ZnCdO alloys grown by molecular-beam epitaxy. The near-band-edge emission is attributed to recombination of excitons localized within band tail states likely caused by nonuniformity in Cd distribution. Energy transfer between the tail states is argued to occur via tunneling of localized excitons. The transfer is shown to be facilitated by increasing Cd content due to a reduction of the exciton binding energy and, therefore, an increase of the exciton Bohr radius in the alloys with a high Cd content. © 2007 American Institute of Physics.

  • 39.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rawal, S.
    Norton, D.P.
    Pearton, S.J.
    Osinsky, A.
    Dong, J.W.
    Origin of near-band-edge emission in ZnCdO alloys2007In: 2007 MRS Fall Meeting,2007, 2007, p. 319-Conference paper (Other academic)
  • 40.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Dilute nitrides-based nanowires-a promising platform for nanoscale photonics and energy technology2019In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 30, no 29, article id 292002Article, review/survey (Refereed)
    Abstract [en]

    Dilute nitrides are novel III-V-N semiconductor alloys promising for a great variety of applications ranging from nanoscale light emitters and solar cells to energy production via photoelectrochemical reactions and to nano-spintronics. These alloys have become available in the one-dimensional geometry only most recently, thanks to the advances in the nanowire (NW) growth utilizing molecular beam epitaxy. In this review we will summarize growth approaches currently utilized for the fabrication of such novel dilute nitride-based NWs, discuss their structural, defect-related and optical properties, as well as provide several examples of their potential applications.

  • 41.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Excitonic and defect properties of nanostructured ZnO2013Conference paper (Refereed)
  • 42.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Magneto-optical spectroscopy of spin injection and spin relaxation in spin light-emitting structures2010In: Handbook of Spintronic Semiconductors, Singapore: Pan Stanford Publishing , 2010, p. 289-323Chapter in book (Other academic)
    Abstract [en]

    This book provides an in-depth review of the rapidly developing field of spintronic semiconductors. It covers a broad range of topics, including growth and basic physical properties of diluted magnetic semiconductors based on II-VI, III-V and IV semiconductors, recent developments in theory and experimental techniques and potential device applications; its aim is to provide postgraduate students, researchers and engineers a comprehensive overview of our present knowledge and future perspectives of spintronic semiconductors.

  • 43.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    New insight on electronic properties of GaNP alloy2005In: 27th Int. Conf. on the Physics of Semicond,2004, 2005, p. 271-Conference paper (Other academic)
  • 44.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Optical and electronic properties of GaInNP alloys - a new material for lattice matching to GaAs2004In: Physics and applications of dilute nitrides / [ed] Irina A. Buyanova and Weimin M. Chen, Kerala, India: Research Signpost , 2004, 1, p. -442Chapter in book (Other academic)
    Abstract [en]

    Since their development in the 1990s, it has been discovered that diluted nitrides have intriguing properties that are not only distinct from those of conventional semiconductor materials, but also are conducive to various applications in optoelectronics and photonics. The book examines these applications and presents a broad and in-depth look at the basic electronic and optical properties of diluted nitrides.

    The aim of Physics and Applications of Diluted Nitrides is to provide graduate students, researchers and engineers with a comprehensive overview of the present knowledge and future perspectives of diluted nitrides.

    Co-authored by a group of leading scientists in the field, this book brings the reader up to speed on the development and current state of diluted nitride applications, as well as the technologies to be developed in the near future.

  • 45.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Optical and electronic properties of GaInNP alloys - a new material for lattice matching to GaAs2008In: Dilute III-V Nitride Semiconductors and Material Systems: Physics and Technology, Berlin: Springer Verlag , 2008, 1, p. 301-316Chapter in book (Other academic)
    Abstract [en]

    A major current challenge for semiconductor devices is to develop materials for the next generation of optical communication systems and solar power conversion applications. Recently, extensive research has revealed that an introduction of only a few percentages of nitrogen into III-V semiconductor lattice leads to a dramatic reduction of the band gap. This discovery has opened the possibility of using these material systems for applications ranging from lasers to solar cells. "Physics and Technology of Dilute III-V Nitride Semiconductors and Novel Dilute Nitride Material Systems" reviews the current status of research and development in dilute III-V nitrides, with 24 chapters from prominent research groups covering recent progress in growth techniques, experimental characterization of band structure, defects carrier transport, transport properties, dynamic behavior of N atoms, device applications, modeling of device design, novel optoelectronic integrated circuits, and novel nitrogen containing III-V materials.

  • 46.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, WeiminLinköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Physics and Applications of Dilute Nitrides2004Collection (editor) (Other academic)
    Abstract [en]

    Since their development in the 1990s, it has been discovered that diluted nitrides have intriguing properties that are not only distinct from those of conventional semiconductor materials, but also are conducive to various applications in optoelectronics and photonics. The book examines these applications and presents a broad and in-depth look at the basic electronic and optical properties of diluted nitrides.

    The aim of Physics and Applications of Diluted Nitrides is to provide graduate students, researchers and engineers with a comprehensive overview of the present knowledge and future perspectives of diluted nitrides.

    Co-authored by a group of leading scientists in the field, this book brings the reader up to speed on the development and current state of diluted nitride applications, as well as the technologies to be developed in the near future.

  • 47.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Recombination processes in dilute nitrides2004In: Physics and Applications of Dilute Nitrides / [ed] Irina A. Buyanova and Weimin M. Chen, New York: Taylor & Francis , 2004, 1, p. 255-280Chapter in book (Other academic)
    Abstract [en]

    Since their development in the 1990s, it has been discovered that diluted nitrides have intriguing properties that are not only distinct from those of conventional semiconductor materials, but also are conducive to various applications in optoelectronics and photonics. The book examines these applications and presents a broad and in-depth look at the basic electronic and optical properties of diluted nitrides.

    The aim of Physics and Applications of Diluted Nitrides is to provide graduate students, researchers and engineers with a comprehensive overview of the present knowledge and future perspectives of diluted nitrides.

    Co-authored by a group of leading scientists in the field, this book brings the reader up to speed on the development and current state of diluted nitride applications, as well as the technologies to be developed in the near future.

  • 48.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Spin Polarization and Injection in ZnMnSe/ZnCdSe Heterostructures2002Conference paper (Refereed)
    Abstract [en]

     Magneto-optical spectroscopy in combination with tunable laser excitation spectroscopy is employed to carry out a detailed study of spin alignment and spin injection in II-VI wide-bandgap semiconductor heterostructures, aiming at optimization of structural design for nano-scale spintronic applications. The use of tunable excitation is shown to provide a valuable opportunity to monitor separately spin relaxation and spin injection processes in the structures. Efficient spin alignment is achieved by using a diluted magnetic semiconductor (DMS) (a layer of ZnMnSe or a ZnMnSe/CdSe superlattice) as thin as 10 nm. The spin alignment efficiency is shown to depend critically on the ratio between the rates of spin relaxation and spin transport within the DMS layer. This allows the realization of spin alignment and spin switching functions by varying the structural design.

  • 49.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Understanding key properties of ZnO nanostructures relevant to advanced optoelectronic applications.2013Conference paper (Refereed)
  • 50.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Bi, W. G.
    Zeng, Y. P.
    Tu, C. W.
    Intrinsic modulation doping in InP-based structures: properties relevant to device applications1999In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 201-202, p. 786-789Article in journal (Refereed)
    Abstract [en]

     In this work we study device-relevant issues, such as doping efficiency and thermal stability, of recently proposed intrinsic modulation doping approach where intrinsic defects (PIn antisites) are used as a carrier source instead of impurity dopants. The InP/InGaAs heterostructure designed to resemble high electron mobility transistor (HEMT) structures, where all the layers were grown at a normal growth temperature 480°C except for the top InP layer which was grown at 265°C, was used as a prototype device. A comparison between the intrinsically doped structure with extrinsically doped HEMTs, which have an identical design except that the top InP layer was instead Si-doped and was grown at 480°C, reveals a high efficiency of the intrinsic doping. The thermal stability of the intrinsically doped HEMT is examined by annealing at temperatures 400-500°C relevant to possible processing steps needed in device fabrication. The observed severe reduction of the carrier concentration after annealing performed without phosphorous gas protection is attributed to the known instability of an InP surface at T>400°C. Thermal stability of the intrinsically doped HEMT is shown to be improved by using an InP cap layer grown at 480°C.

1234567 1 - 50 of 471
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