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  • 1.
    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.

  • 2.
    Wang, Suhao
    et al.
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Fazzi, Daniele
    Univ Cologne, Germany.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Jafari, Mohammad Javad
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Chen, Zhihua
    Flexterra Corp, IL 60077 USA.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Andreasen, Jens W.
    Tech Univ Denmark, Denmark.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Facchetti, Antonio
    Flexterra Corp, IL 60077 USA; Northwestern Univ, IL 60208 USA; Northwestern Univ, IL 60208 USA.
    Fabiano, Simone
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Effect of Backbone Regiochemistry on Conductivity, Charge Density, and Polaron Structure of n-Doped Donor-Acceptor Polymers2019In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 9, p. 3395-3406Article in journal (Refereed)
    Abstract [en]

    We investigated the influence of backbone regiochemistry on the conductivity, charge density, and polaron structure in the widely studied n-doped donor-acceptor polymer poly[N,N-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5-(2,2-bithiophene) [P-(NDI2OD-T2)]. In contrast to classic semicrystalline polymers such as poly(3-hexylthiophene) (P3HT), the regioirregular (RI) structure of the naphthalenediimide (NDI)-bithiophene (T2) backbone does not alter the intramolecular steric demand of the chain versus the regioregular (RR) polymer, yielding RI-P(NDI2OD-T2) with similar energetics and optical features as its RR counterpart. By combining the electrical, UV-vis/infrared, X-ray diffraction, and electron paramagnetic resonance data and density functional theory calculations, we quantitatively characterized the conductivity, aggregation, crystallinity, and charge density, and simulated the polaron structures, molecular vibrations, and spin density distribution of RR-/RI-P(NDI2OD-T2). Importantly, we observed that RI-P(NDI2OD-T2) can be doped to a greater extent compared to its RR counterpart. This finding is remarkable and contrasts benchmark P3HT, allowing us to uniquely study the role of regiochemistry on the charge-transport properties of n-doped donor-acceptor polymers.

  • 3.
    Zhang, Bin
    et al.
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Qiu, Weiyang
    Chinese Acad Sci, Peoples R China.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Chen, Pingping
    Chinese Acad Sci, Peoples R China.
    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.
    Wang, Xingjun
    Chinese Acad Sci, Peoples R China.
    Effect of exciton transfer on recombination dynamics in vertically nonuniform GaAsSb epilayers2019In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, no 25, article id 252101Article in journal (Refereed)
    Abstract [en]

    Low-temperature photoluminescence (PL), photoreflectance (PR), and temperature dependent time-resolved PL spectroscopies are employed to investigate optical emission processes and exciton dynamics in graded GaAsSb epilayers. The nonuniformity in the Sb composition along the growth direction is disclosed by low-temperature PL and PR measurements. Furthermore, significant differences in PL dynamics are found at low temperatures for the PL emissions originating from spatial regions with the low and high Sb compositions, with a fast decay and a slow rise at the early stage of the PL transient, respectively. This finding is attributed to exciton transfer from the low Sb region to the high Sb region. The obtained results are important for a general understanding of optical transitions and exciton/carrier dynamics in material systems with a graded alloy composition.

  • 4.
    Zhang, Pimin
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Sadeghimeresht, Esmaeil
    Dept of Engineering Science, University West, Trollhättan, Sweden.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Markocsan, Nicoclaie
    Dept of Engineering Science, University West, Trollhättan, Sweden.
    Joshi, Shrikant
    Dept of Engineering Science, University West, Trollhättan, Sweden.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Effects of Surface Finish on the Initial Oxidation of HVAF-sprayed NiCoCrAlY Coatings2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Journal of Surface and Coatings Technology, ISSN 0257-8972, Vol. 364, p. 43-56Article in journal (Refereed)
    Abstract [en]

    Oxide scale formed on HVAF-sprayed NiCoCrAlY coatings and the effect of surface treatment were investigated by a multi-approach study combining photo-stimulated luminescence, microstructural observation and mass gain. The initial oxidationbehaviour of as-sprayed, polished and shot-peened coatings at 1000 °C is studied. Both polished and shot-peened coatings exhibited superior performance due to rapid formation of α-Al2O3 fully covering the coating and suppressing the growth of transient alumina, assisted by a high density of α-Al2O3 nuclei on surface treatment induced defects. Moreover, the fast development of a two-layer alumina scale consisting of an inward-grown inner α-Al2O3 layer and an outer layer transformed from outward-grown transient alumina resulted in a higher oxide growth rate of the as-sprayed coating.

  • 5.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, Shula
    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, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Cai, Li
    Xi An Jiao Tong Univ, Peoples R China.
    Shen, Shaohua
    Xi An Jiao Tong Univ, Peoples R China.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Identification of a Nitrogen-related acceptor in ZnO nanowires2019In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 22, p. 10921-10926Article in journal (Refereed)
    Abstract [en]

    Nanostructured ZnO, such as ZnO nanowires (NWs), is a promising material system for a wide range of electronic applications ranging from light emission to water splitting. Utilization of ZnO requires development of effective and controllable p-type doping. Nitrogen is considered among key p-type dopants though the exact origin of N-induced acceptors is not fully understood, especially in the case of nanostructured ZnO. In this work we employ electron paramagnetic resonance (EPR) spectroscopy to characterize N-related acceptors in ZnO NWs. N doping was achieved using ion implantation commonly employed for these purposes. We show that the Fermi level position is lowered in the N implanted NWs, indicating the formation of compensating acceptors. The formed acceptor is unambiguously proven to involve an N atom based on a resolved hyperfine interaction with a 14N nucleus with a nuclear spin I = 1. The revealed center is shown to act as a deep acceptor with an energy level located at about 1.1 eV above the top of the valence band. This work represents the first unambiguous identification of acceptors deliberately introduced in ZnO nanostructures. It also shows that the configuration and electronic structure of the N-related acceptors in nanostructures differ from those in ZnO bulk and thin-films. The present findings are of importance for understanding the electronic properties of nanostructured ZnO required for its future electronic applications.

  • 6.
    Jansson, Mattias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Francaviglia, Luca
    Ecole Polytech Fed Lausanne, Switzerland.
    La, Rui
    Univ Calif San Diego, CA 92093 USA.
    Balagula, Roman
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Stehr, Jan Eric
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Tu, Charles W.
    Univ Calif San Diego, CA 92093 USA.
    Morral, Anna Fontcuberta I
    Ecole Polytech Fed Lausanne, Switzerland; Ecole Polytech Fed Lausanne, Switzerland.
    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.
    Increasing N content in GaNAsP nanowires suppresses the impact of polytypism on luminescence2019In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 30, no 40, article id 405703Article in journal (Refereed)
    Abstract [en]

    Cathodoluminescence (CL) and micro-photoluminescence spectroscopies are employed to investigate effects of structural defects on carrier recombination in GaNAsP nanowires (NWs) grown by molecular beam epitaxy on Si substrates. In the NWs with a low N content of 0.08%, these defects are found to promote non-radiative (NR) recombination, which causes spatial variation of the CL peak position and its intensity. Unexpectedly, these detrimental effects can be suppressed even by a small increase in the nitrogen composition from 0.08% to 0.12%. This is attributed to more efficient trapping of excited carriers/excitons to the localized states promoted by N-induced localization and also the presence of other NR channels At room temperature, the structural defects no longer dominate in carrier recombination even in the NWs with the lower nitrogen content, likely due to increasing importance of other recombination channels. Our work underlines the need in eliminating important thermally activated NR defects, other than the structural defects, for future optoelectronic applications of these NWs.

  • 7.
    Goransson, D. J. O.
    et al.
    Lund Univ, Sweden.
    Borgstrom, M. T.
    Lund Univ, Sweden.
    Huang, Yuqing
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Messing, M. E.
    Lund Univ, Sweden.
    Hessman, D.
    Lund Univ, 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.
    Xu, H. Q.
    Lund Univ, Sweden; Peking Univ, Peoples R China; Peking Univ, Peoples R China; Beijing Acad Quantum Informat Sci, Peoples R China.
    Measurements of Strain and Bandgap of Coherently Epitaxially Grown Wurtzite InAsP-InP Core-Shell Nanowires2019In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, no 4, p. 2674-2681Article in journal (Refereed)
    Abstract [en]

    We report on experimental determination of the strain and bandgap of InAsP in epitaxially grown InAsP-InP core-shell nanowires. The core-shell nanowires are grown via metal-organic vapor phase epitaxy. The as-grown nanowires are characterized by transmission electron microscopy, X-ray diffraction, micro-photoluminescence (mu PL) spectroscopy, and micro-Raman (mu-Raman) spectroscopy measurements. We observe that the core-shell nanowires are of wurtzite (WZ) crystal phase and are coherently strained with the core and the shell having the same number of atomic planes in each nanowire. We determine the predominantly uniaxial strains formed in the core-shell nanowires along the nanowire growth axis and demonstrate that the strains can be described using an analytical expression. The bandgap energies in the strained WZ InAsP core materials are extracted from the mu PL measurements of individual core-shell nanowires. The coherently strained core-shell nanowires demonstrated in this work offer the potentials for use in constructing novel optoelectronic devices and for development of piezoelectric photovoltaic devices.

  • 8.
    Yukimune, M.
    et al.
    Ehime Univ, Japan.
    Fujiwara, R.
    Ehime Univ, Japan.
    Mita, T.
    Ehime Univ, Japan.
    Tsuda, N.
    Ehime Univ, Japan.
    Natsui, J.
    Ehime Univ, Japan.
    Shimizu, Y.
    Toray Res Ctr, Japan.
    Jansson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Balagula, Roman
    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.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Ishikawa, F.
    Ehime Univ, Japan.
    Molecular beam epitaxial growth of dilute nitride GaNAs and GaInNAs nanowires2019In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 30, no 24, article id 244002Article in journal (Refereed)
    Abstract [en]

    We report the growth of dilute nitride GaNAs and GaInNAs core-multishell nanowires (NWs) using molecular beam epitaxy assisted by a plasma source. Using the self-catalyst vapor-liquid-solid growth mode, these NWs were grown on Si(111) and silicon on insulator substrates. The GaNAs and GaInNAs shells contain nitrogen up to 3%. Axial cross-sectional scanning transmission electron microscopy measurements and energy-dispersive x-ray spectrometry confirm the formation of the core-multishell NW structure. We obtained high-quality GaNAs NWs with nitrogen compositions up to 2%. On the other hand, GaNAs containing 3% nitrogen, and GaInNAs NWs, show distorted structures; moreover, the optical emissions seem to be related to defects. Further optimisations of the growth conditions will improve these properties, promising future applications in nanoscale optoelectronics.

    The full text will be freely available from 2020-03-26 11:28
  • 9.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Yukimune, Mitsuki
    Ehime Univ, Japan.
    Fujiwara, Ryo
    Ehime Univ, Japan.
    Ishikawa, Fumitaro
    Ehime Univ, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Near-Infrared Lasing at 1 mu m from a Dilute-Nitride-Based Multishell Nanowire2019In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, no 2, p. 885-890Article in journal (Refereed)
    Abstract [en]

    A coherent photon source emitting at near-infrared (NIR) wavelengths is at the heart of a wide variety of applications ranging from telecommunications and optical gas sensing to biological imaging and metrology. NIR-emitting semiconductor nanowires (NWs), acting both as a miniaturized optical resonator and as a photonic gain medium, are among the best-suited nanomaterials to achieve such goals. In this study, we demonstrate the NIR lasing at 1 mu m from GaAs/GaNAs/GaAs core/shell/cap dilute nitride nanowires with only 2.5% nitrogen. The achieved lasing is characterized by an S-shape pump-power dependence and narrowing of the emission line width. Through examining the lasing performance from a set of different single NWs, a threshold gain, g(th), of 4100-4800 cm(-1), was derived with a spontaneous emission coupling factor, beta, up to 0.8, which demonstrates the great potential of such nanophotonic material. The lasing mode was found to arise from the fundamental HE11a mode of the Fabry-Perot cavity from a single NW, exhibiting optical polarization along the NW axis. Based on temperature dependence of the lasing emission, a high characteristic temperature, T-0, of 160 (+/- 10) K is estimated. Our results, therefore, demonstrate a promising alternative route to achieve room-temperature NIR NW lasers thanks to the excellent alloy tunability and superior optical performance of such dilute nitride materials.

  • 10.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Yukimune, Mitsuki
    Ehime Univ, Japan.
    Fujiwara, Ryo
    Ehime Univ, Japan.
    Ishikawa, Fumitaro
    Ehime Univ, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Near-Infrared Lasing at 1 mu m from a Dilute-Nitride-Based Multishell Nanowire2019In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, no 2, p. 885-890Article in journal (Refereed)
    Abstract [en]

    A coherent photon source emitting at near-infrared (NIR) wavelengths is at the heart of a wide variety of applications ranging from telecommunications and optical gas sensing to biological imaging and metrology. NIR-emitting semiconductor nanowires (NWs), acting both as a miniaturized optical resonator and as a photonic gain medium, are among the best-suited nanomaterials to achieve such goals. In this study, we demonstrate the NIR lasing at 1 mu m from GaAs/GaNAs/GaAs core/shell/cap dilute nitride nanowires with only 2.5% nitrogen. The achieved lasing is characterized by an S-shape pump-power dependence and narrowing of the emission line width. Through examining the lasing performance from a set of different single NWs, a threshold gain, g(th), of 4100-4800 cm(-1), was derived with a spontaneous emission coupling factor, beta, up to 0.8, which demonstrates the great potential of such nanophotonic material. The lasing mode was found to arise from the fundamental HE11a mode of the Fabry-Perot cavity from a single NW, exhibiting optical polarization along the NW axis. Based on temperature dependence of the lasing emission, a high characteristic temperature, T-0, of 160 (+/- 10) K is estimated. Our results, therefore, demonstrate a promising alternative route to achieve room-temperature NIR NW lasers thanks to the excellent alloy tunability and superior optical performance of such dilute nitride materials.

    The full text will be freely available from 2020-01-04 14:25
  • 11.
    Li, Zaifang
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Huazhong Univ Sci and Technol, Peoples R China.
    Sun, Hengda
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Hsiao, Ching-Lien
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Yao, Yulong
    Univ Kentucky, KY 40506 USA.
    Xiao, Yiqun
    Chinese Univ Hong Kong, Peoples R China.
    Shahi, Maryam
    Univ Kentucky, KY 40506 USA.
    Jin, Yingzhi
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Cruce, Alex
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Jiang, Youyu
    Huazhong Univ Sci and Technol, Peoples R China.
    Meng, Wei
    Huazhong Univ Sci and Technol, Peoples R China.
    Qin, Fei
    Huazhong Univ Sci and Technol, Peoples R China.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Fabiano, Simone
    Linköping University, Department of Science and Technology, Physics and Electronics. 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.
    Lu, Xinhui
    Chinese Univ Hong Kong, Peoples R China.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Brill, Joseph W.
    Univ Kentucky, KY 40506 USA.
    Zhou, Yinhua
    Huazhong Univ Sci and Technol, Peoples R China; South China Univ Technol, Peoples R China.
    Crispin, Xavier
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    A Free-Standing High-Output Power Density Thermoelectric Device Based on Structure-Ordered PEDOT:PSS2018In: Advanced Electronic Materials, ISSN 2199-160X, Vol. 4, no 2, article id 1700496Article in journal (Refereed)
    Abstract [en]

    A free-standing high-output power density polymeric thermoelectric (TE) device is realized based on a highly conductive (approximate to 2500 S cm(-1)) structure-ordered poly(3,4-ethylenedioxythiophene):polystyrene sulfonate film (denoted as FS-PEDOT:PSS) with a Seebeck coefficient of 20.6 mu V K-1, an in-plane thermal conductivity of 0.64 W m(-1) K-1, and a peak power factor of 107 mu W K-2 m(-1) at room temperature. Under a small temperature gradient of 29 K, the TE device demonstrates a maximum output power density of 99 +/- 18.7 mu W cm(-2), which is the highest value achieved in pristine PEDOT:PSS based TE devices. In addition, a fivefold output power is demonstrated by series connecting five devices into a flexible thermoelectric module. The simplicity of assembling the films into flexible thermoelectric modules, the low out-of-plane thermal conductivity of 0.27 W m(-1) K-1, and free-standing feature indicates the potential to integrate the FS-PEDOT:PSS TE modules with textiles to power wearable electronics by harvesting human bodys heat. In addition to the high power factor, the high thermal stability of the FS-PEDOT:PSS films up to 250 degrees C is confirmed by in situ temperature-dependent X-ray diffraction and grazing incident wide angle X-ray scattering, which makes the FS-PEDOT:PSS films promising candidates for thermoelectric applications.

  • 12.
    Puttisong, Yuttapoom
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Xia, Yuxin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, X.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Gao, Feng
    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, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Inganäs, Olle
    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, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Charge Generation via Relaxed Charge-Transfer States in Organic Photovoltaics by an Energy-Disorder-Driven Entropy Gain2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 24, p. 12640-12646Article in journal (Refereed)
    Abstract [en]

    In organic photovoltaics, efficient charge generation relies on our ability to convert excitons into free charges. Efficient charge separation from "energetic excitons" has been understood to be governed by delocalization effects promoted by molecular aggregation. A remaining puzzle is, however, the mechanism underlying charge generation via relaxed interfacial charge-transfer (CT) excitons that also exhibit an internal quantum efficiency close to unity. Here, we provide evidence for efficient charge generation via CT state absorption over a temperature range of 50-300 K, despite an intrinsically strong Coulomb binding energy of about 400 meV that cannot be modified by fullerene aggregation. We explain our observation by entropy-driven charge separation, with a key contribution from energy disorder. The energy disorder reduces the charge generation barrier by substantially gaining the entropy as electron hole distance increases, resulting in efficient CT exciton dissociation. Our results underline an emerging consideration of energy disorder in thermodynamic stability of charge pairs and highlight the energy disorder as a dominant factor for generating charges via the CT state. A discussion for a trade-off in harvesting charges from relaxed CT excitons is also provided.

  • 13.
    Qian, Deping
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zheng, Zilong
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Yao, Huifeng
    Chinese Acad Sci, Peoples R China.
    Tress, Wolfgang
    Ecole Polytech Fed Lausanne, Switzerland.
    Hopper, Thomas R.
    Imperial Coll London, England.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Li, Sunsun
    Chinese Acad Sci, Peoples R China.
    Liu, Jing
    Hong Kong Univ Sci and Technol, Peoples R China; Hong Kong Univ Sci and Technol, Peoples R China.
    Chen, Shangshang
    Hong Kong Univ Sci and Technol, Peoples R China; Hong Kong Univ Sci and Technol, Peoples R China.
    Zhang, Jiangbin
    Imperial Coll London, England; Univ Cambridge, England.
    Liu, Xiaoke
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gao, Bowei
    Chinese Acad Sci, Peoples R China.
    Ouyang, Liangqi
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Jin, Yingzhi
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    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.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Coropceanu, Veaceslav
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Bredas, Jean-Luc
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Yan, He
    Hong Kong Univ Sci and Technol, Peoples R China; Hong Kong Univ Sci and Technol, Peoples R China.
    Hou, Jianhui
    Chinese Acad Sci, Peoples R China.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Bakulin, Artem A.
    Imperial Coll London, England.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Design rules for minimizing voltage losses in high-efficiency organic solar cells2018In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 17, no 8, p. 703-+Article in journal (Refereed)
    Abstract [en]

    The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor-acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor-acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.

  • 14.
    Huang, Yuqing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Yang, X. J.
    Suzhou QiangMing Optoelect Co Ltd, Peoples R China.
    Murayama, A.
    Hokkaido Univ, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Effect of a Phonon Bottleneck on Exciton and Spin Generation in Self-Assembled In1-xGaxAs Quantum Dots2018In: Physical Review Applied, ISSN 2331-7019, Vol. 9, no 4, article id 044037Article in journal (Refereed)
    Abstract [en]

    We provide direct experimental evidence for the effect of a phonon bottleneck on exciton and spin generation in self-assembled In0.5Ga0.5As quantum dots (QDs). With the aid of tunable laser spectroscopy, we resolve and identify efficient exciton generation channels in the QDs mediated by longitudinal-optical (LO) phonons from an otherwise inhomogeneously broadened QD emission background that suffers from the phonon bottleneck effect in exciton generation. Spin-generation efficiency is found to be enhanced under the LO-assisted excitation condition due to suppressed spin relaxation accompanying accelerated exciton generation. These findings underline the importance of fine-tuning QD energy levels that will benefit potential spin-optoelectronic applications of QDs by reducing spin loss due to the phonon bottleneck.

  • 15.
    Guo, Yiting
    et al.
    Chinese Acad Sci, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Liu, Yanfeng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zhu, Qinglian
    Xi An Jiao Tong Univ, Peoples R China.
    Li, Cheng
    Chinese Acad Sci, Peoples R China.
    Jin, Yingzhi
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Puttisong, Yuttapoom
    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.
    Liu, Feng
    Hebei Univ, Peoples R China.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ma, Wei
    Xi An Jiao Tong Univ, Peoples R China.
    Li, Weiwei
    Chinese Acad Sci, Peoples R China.
    Effect of Side Groups on the Photovoltaic Performance Based on Porphyrin-Perylene Bisimide Electron Acceptors2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 38, p. 32454-32461Article in journal (Refereed)
    Abstract [en]

    In this work, we developed four porphyrin-based small molecular electron acceptors for non-fullerene organic solar cells, in which different side groups attached to the porphyrin core were selected in order to achieve optimized performance. The molecules contain porphyrin as the core, perylene bisimides as end groups, and the ethynyl unit as the linker. Four side groups, from 2,6-di(dodecyloxy)phenyl to (2-ethylhexyl)thiophen-2-yl, pentadecan-7-yl, and 3,5-di(dodecyloxy)phenyl unit, were applied into the electron acceptors. The new molecules exhibit broad absorption spectra from 300 to 900 nm and high molar extinction coefficients. The molecules as electron acceptors were applied into organic solar cells, showing increased power conversion efficiencies from 1.84 to 5.34%. We employed several techniques, including photoluminescence spectra, electroluminescence spectra, atomic force microscopy, and grazing-incidence wide-angle X-ray to probe the blends to find the effects of the side groups on the photovoltaic properties. We found that the electron acceptors with 2,6-di(dodecyloxy)phenyl units show high-lying frontier energy levels, good crystalline properties, and low nonradiative recombination loss, resulting in possible large phase separation and low energy loss, which is responsible for the low performance. Our results provide a detailed study about the side groups of non-fullerene materials, demonstrating that porphyrin can be used to design electron acceptors toward near-infrared absorption.

  • 16.
    Chen, Shula
    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.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Effects of Strong Band-Tail States on Exciton Recombination Dynamics in Dilute Nitride GaP/GaNP Core/Shell Nanowires2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 33, p. 19212-19218Article in journal (Refereed)
    Abstract [en]

    Exciton dynamics in dilute nitride GaP/GaNP core/shell nanowires (NWs) with pronounced band-tail states formed by nitrogen clusters is investigated using time-resolved photoluminescence (PL) spectroscopy. The emission of excitons localized at the N-related states in the GaNP shell is found to exhibit a stretched exponential decay, with the 1/e lifetime dramatically shortened with decreasing excitation wavelength and reduced shell thickness. The observed PL transient behavior is explained by markedly different exciton lifetimes between the surface and bulk regions of the GaNP shell, that is, similar to 20 ps versus similar to 10 ns, respectively. Despite being trapped at the deep localized N states, the photoexcited excitons are concluded to suffer from pronounced surface recombination via tunneling to the surface states within a distance of 10 nm from the surface, which results in the depth-dependent PL dynamics. The surface recombination rate is, however, lower than that previously reported for GaP, indicative of partial passivation of the surface states by nitrogen. From temperature-dependent PL measurements, characteristic thermal activation energies for the surface and bulk-related nonradiative recombination channels are deduced. The obtained results provide insight into the exciton/carrier dynamics in NW systems with strong localization or alloy disorder, which is important for future nanophotonic and photovoltaic applications of such structures.

  • 17.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Svensson, B. G.
    Univ Oslo, Norway.
    Buyanova, Irina
    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.
    Efficient Auger Charge-Transfer Processes in ZnO2018In: Physical Review Applied, ISSN 2331-7019, Vol. 9, no 5, article id 054014Article in journal (Refereed)
    Abstract [en]

    Photoluminescence and magneto-optical measurements are performed on a line peaking at 3.354 eV (labeled as NBX) in electron-irradiated ZnO. Even though the energy position of the NBX line is close to that for bound excitons in ZnO, it has distinctively different magneto-optical properties. Photoelectron paramagnetic resonance measurements reveal a connection and a charge-transfer process involving NBX and Fe and Al centers. The experimental results are explained within a model which assumes that the NBX is a neutral donor bound exciton at a defect center located near a Fe impurity and an Auger-type charge-transfer process occurs between NBX and Fe3+. While the NBX dissociates, its hole is captured by an excited state of Fe3+ and the released energy is transferred to the NBX electron, which is excited to the conduction band and subsequently trapped by a substitutional Al-zn shallow donor.

  • 18.
    Yukimune, M.
    et al.
    Ehime Univ, Japan.
    Fujiwara, R.
    Ehime Univ, Japan.
    Ikeda, H.
    Ehime Univ, Japan.
    Yano, K.
    Ehime Univ, Japan.
    Takada, K.
    Ehime Univ, Japan.
    Jansson, Mattias
    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.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Ishikawa, F.
    Ehime Univ, Japan.
    GaAs/GaNAs core-multishell nanowires with nitrogen composition exceeding 2%2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 113, no 1, article id 011901Article in journal (Refereed)
    Abstract [en]

    We report the growth of GaAs/GaNAs/GaAs core-multishell nanowires having N compositions exceeding 2%. The structures were grown by plasma-assisted molecular beam epitaxy using constituent Ga-induced vapor-liquid-solid growth on Si(111) substrates. The GaNAs shell nominally contains 0%, 2%, and 3% nitrogen. The axial cross-sectional scanning transmission electron microscopy measurements confirm the existence of core-multishell structure. The room temperature micro-photoluminescence measurements reveal a red-shift of the detected emission with increasing N content in the nanowires, consistent with the expected changes in the GaNAs bandgap energy due to the bowing effect. Published by AIP Publishing.

  • 19.
    Jansson, Mattias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Ishikawa, F.
    Ehime Univ, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    N-induced Quantum Dots in GaAs/Ga(N, As) Core/Shell Nanowires: Symmetry, Strain, and Electronic Structure2018In: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, no 4, article id 044040Article in journal (Refereed)
    Abstract [en]

    Nanowires (NWs) with embedded zero-dimensional (0D) quantum dots (QDs) have interesting fundamental properties attractive for a variety of applications. The properties of such embedded QDs can be controlled by 0D quantum confinement and also via strain engineering in axial or radial heterostructures of the nanowire system. We evaluate the electronic structure of QDs, which are formed in the Ga(N, As) shell of the GaAs/Ga(N, As) core-shell NWs due to alloy fluctuations. It is found that the principal quantization axis of the studied QDs is primarily oriented along the NW axis, based on the performed polarizationresolved magneto-photoluminescence measurements. We also show that the QDs exhibit a large spectrally dependent variation of the valence band character, which changes from pure heavy-hole states for the low-energy QD emitters to the mixed light-hole heavy-hole states for the QDs emitting at high energies. We ascribe these changes to combined effects of the uniaxial strain caused by the lattice mismatch between the GaAs core and the Ga(N, As) shell, and the local strain/lattice distortion within the short-range fluctuations in the N content. The obtained results underline the importance of the local strain for valence band engineering in hybrid NW structures with embedded QDs.

  • 20.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Huang, Yuqing
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Visser, Dennis
    KTH Royal Inst Technol, Sweden.
    Anand, Srinivasan
    KTH Royal Inst Technol, Sweden.
    Buyanova, Irina
    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.
    Room-temperature polarized spin-photon interface based on a semiconductor nanodisk-in-nanopillar structure driven by few defects2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 3575Article in journal (Refereed)
    Abstract [en]

    Owing to their superior optical properties, semiconductor nanopillars/nanowires in one-dimensional (1D) geometry are building blocks for nano-photonics. They also hold potential for efficient polarized spin-light conversion in future spin nano-photonics. Unfortunately, spin generation in 1D systems so far remains inefficient at room temperature. Here we propose an approach that can significantly enhance the radiative efficiency of the electrons with the desired spin while suppressing that with the unwanted spin, which simultaneously ensures strong spin and light polarization. We demonstrate high optical polarization of 20%, inferring high electron spin polarization up to 60% at room temperature in a 1D system based on a GaNAs nanodisk-in-GaAs nanopillar structure, facilitated by spin-dependent recombination via merely 2-3 defects in each nanodisk. Our approach points to a promising direction for realization of an interface for efficient spin-photon quantum information transfer at room temperature-a key element for future spin-photonic applications.

  • 21.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Jansson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Stehr, Jan Eric
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Huang, Yuqing
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Ishikawa, Fumitaro
    Ehime University, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Dilute Nitride Nanowire Lasers Based on a GaAs/GaNAs Core/Shell Structure2017In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 3, p. 1775-1781Article in journal (Refereed)
    Abstract [en]

    Nanowire (NW) lasers operating in the near infrared spectral range are of significant technological importance for applications in telecommunications, sensing, and medical diagnostics. So far, lasing within this spectral range has been achieved using GaAs/AlGaAs, GaAs/GaAsP, and InGaAs/GaAs core/shell NWs. Another promising III-V material, not yet explored in its lasing capacity, is the dilute nitride GaNAs. In this work, we demonstrate, for the first time, optically pumped lasing from the GaNAs shell of a single GaAs/GaNAs core/shell NW. The characteristic "S"-shaped pump power dependence of the lasing intensity, with the concomitant line width narrowing, is observed, which yields a threshold gain, g(th), of 3300 cm(-1) and a spontaneous emission coupling factor beta, of 0.045. The dominant lasing peak is identified to arise from the HE21b, cavity mode, as determined from its pronounced emission polarization along the NW axis combined with theoretical calculations of lasing threshold for guided modes inside the nanowire. Even without intentional pas sivation of the NW surface, the lasing emission can be sustained up to 150 K. This is facilitated by the improved surface quality due to nitrogen incorporation, which partly suppresses the surface-related nonradiative recombination centers via nitridation. Our work therefore represents the first step toward development of room-temperature infrared NW lasers based on dilute nitrides with extended tunability in the lasing wavelength.

  • 22.
    Jansson, Mattias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    La, Rui
    University of Calif San Diego, CA 92093 USA.
    Stehr, Jan Eric
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Tu, Charles W.
    University of Calif San Diego, CA 92093 USA; University of Calif San Diego, CA 92093 USA.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Effects of Nitrogen Incorporation on Structural and Optical Properties of GaNAsP Nanowires2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 12, p. 7047-7055Article in journal (Refereed)
    Abstract [en]

    In this work, we carry out a comprehensive investigation of structural and optical effects in GaNAsP nanowires (NWs), which are novel materials promising for advanced photovoltaic applications. Despite a significant mismatch in electronegativity between N and As/P atoms, we show that incorporation of nitrogen does not degrade structural quality of the nanowires and the fabricated NW arrays have excellent compositional uniformity among individual wires. From temperature-dependent photoluminescence (PL) measurements, statistical fluctuations of the alloy composition are shown to lead to localization of photoexcited carriers at low temperatures but do not affect material properties at room temperature. According to time-resolved PL measurements, the room-temperature carrier lifetime increases in the GaNAsP NWs as compared with the GaAsP NWs, which indicates reduced nonradiative recombination. Moreover, in spite of the very low N content in the studied NWs (up to 0.16%), their bandgap energy can be tuned by more than 100 meV. This is accompanied by about 30% reduction in the temperature dependence of the bandgap energy. The presented results demonstrate that alloying of GaAsP with nitrogen provides an additional means of design optimization, beneficial for, e.g., NW-based intermediate band solar cells that are highly dependent on the optimum bandgap structure.

  • 23.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Ishikawa, Fumitaro
    Ehime University, Matsuyama, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    GaNAs-⁠Based Nanowires for Near-⁠infrared Optoelectronics2017In: Novel Compound Semiconductor Nanowires: Materials, Devices, and Applications / [ed] F. Ishikawa; I. A. Buyanova, Pan Stanford Publishing, 2017Chapter in book (Other academic)
  • 24.
    Huang, Yuqing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Song, Y. X.
    Wang, S. M.
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg 412 96, Sweden.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Generation of helicity-dependent surface spin photocurrent in 3D topological insulator Bi2Te3 (invited talk)2017Conference paper (Refereed)
  • 25.
    Rudko, Galyna Yu.
    et al.
    National Academic Science Ukraine, Ukraine.
    Vorona, Igor P.
    National Academic Science Ukraine, Ukraine.
    Fediv, Volodymyr I.
    Bukovinian State Medical University, Ukraine.
    Kovalchuk, Andrii
    National Academic Science Ukraine, Ukraine.
    Stehr, Jan Eric
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Shanina, Bela D.
    National Academic Science Ukraine, Ukraine.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Luminescent and Optically Detected Magnetic Resonance Studies of CdS/PVA Nanocomposite2017In: Nanoscale Research Letters, ISSN 1931-7573, E-ISSN 1556-276X, Vol. 12, article id 130Article in journal (Refereed)
    Abstract [en]

    A series of solid nanocomposites containing CdS nanoparticles in polymeric matrix with varied conditions on the interface particle/polymer was fabricated and studied by photoluminescence (PL) and optically detected magnetic resonance (ODMR) methods. The results revealed interface-related features in both PL and ODMR spectra. The revealed paramagnetic centers are concluded to be involved in the processes of photo-excited carriers relaxation.

  • 26.
    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 Photonics2017In: Novel Compound Semiconductor Nanowires: Materials, Devices, and Applications / [ed] F. Ishikawa; I. A. Buyanova, Pan Stanford Publishing, 2017Chapter in book (Other academic)
  • 27.
    Puttisong, Yuttapoom
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Cavendish Laboratory, University of Cambridge.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. 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, Functional Electronic Materials. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Room Temperature Defect-Engineered Spin Functionalities: Concept and Optimization2017In: Contemporary Topics in Semiconductor Spintronics / [ed] Supriyo Bandyopadhyay (Virginia Commonwealth University, USA), Marc Cahay (University of Cincinnati, USA), Jean-Pierre Leburton (University of Illinois at Urbana-Champaign, USA), World Scientific, 2017Chapter in book (Other academic)
  • 28.
    Volkov, Anton
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Singh, Sandeep Kumar
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Stavrinidou, Eleni
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Gabrielsson, Roger
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Franco Gonzalez, Felipe
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Cruce, Alex
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Simon, Daniel
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Berggren, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Zozoulenko, Igor
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Spectroelectrochemistry and Nature of Charge Carriers in Self-Doped Conducting Polymer2017In: Advanced Electronic Materials, ISSN 2199-160X, Vol. 3, no 8, article id 1700096Article in journal (Refereed)
    Abstract [en]

    A recently developed water-soluble self-doped sodium salt of bis[3,4-ethylenedioxythiophene] 3thiophene butyric acid (ETE-S) is electropolymerized and characterized by means of spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and cyclic voltammetry, combined with the density functional theory (DFT) and time-dependent DFT calculations. The focus of the studies is to underline the nature of the charge carriers when the electrochemically polymerized ETE-S films undergo a reversible transition from reduced to electrically conductive oxidized states. Spectroelectrochemistry shows clear distinctions between absorption features from reduced and charged species. In the reduced state, the absorption spectrum of ETE-S electropolymerized film shows a peak that is attributed to HOMO. LUMO transition. As the oxidation level increases, this peak diminishes and the absorption of the film is dominated by spinless bipolaronic states with some admixture of polaronic states possessing a magnetic momentum. For fully oxidized samples, the bipolaronic states fully dominate, and the features in the absorption spectra are related to the drastic changes of the band structure, exhibiting a strong decrease of the band gap when a polymeric film undergoes oxidation.

  • 29.
    Huang, Yuqing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Song, Y. X.
    Chinese Academic Science, Peoples R China.
    Wang, S. M.
    Chinese Academic Science, Peoples R China; Chalmers, Sweden.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Spin injection and helicity control of surface spin photocurrent in a three dimensional topological insulator2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 15401Article in journal (Refereed)
    Abstract [en]

    A three-dimensional (3D) topological insulator (TI) is a unique quantum phase of matter with exotic physical properties and promising spintronic applications. However, surface spin current in a common 3D TI remains difficult to control and the out-of-plane spin texture is largely unexplored. Here, by means of surface spin photocurrent in Bi2Te3 TI devices driven by circular polarized light, we identify the subtle effect of the spin texture of the topological surface state including the hexagonal warping term on the surface current. By exploring the out-of-plane spin texture, we demonstrate spin injection from GaAs to TI and its significant contribution to the surface current, which can be manipulated by an external magnetic field. These discoveries pave the way to not only intriguing new physics but also enriched spin functionalities by integrating TI with conventional semiconductors, such that spin-enabled optoelectronic devices may be fabricated in such hybrid structures.

  • 30.
    Huang, Yuqing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Song, Y. X.
    Wang, S. M.
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg 412 96, Sweden.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Spin texture and spin injection in a 3D topological insulator (invited talk)2017Conference paper (Refereed)
  • 31.
    Jansson, Mattias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Ishikawa, Fumitaro
    Ehime University, Japan.
    Characterization of Quantum Dot-like Emission from GaAs/GaNAs Core/Shell Nanowires2016In: 2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO), IEEE , 2016, p. 42-44Conference paper (Refereed)
    Abstract [en]

    this work we investigate properties of ultra-narrow photoluminescence lines originating from recombination of excitons trapped by short-range potential fluctuations, caused by alloy disorder in GaAs/GaNAs core/shell nanowires. From power-dependent photoluminescence measurements we show that the emission behavior is consistent with biexciton-exciton cascade recombination in quantum dots. We also show that the thermal activation energy from the related localized states is of the order of 9-30 meV, suggesting a rather shallow confinement potential.

  • 32.
    Chen, Shula
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Jansson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Ishikawa, Fumitaro
    Ehime University, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Core-shell carrier and exciton transfer in GaAs/GaNAs coaxial nanowires2016In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 34, no 4, p. 04J104-Article in journal (Refereed)
    Abstract [en]

    Comprehensive studies of GaAs/GaNAs coaxial nanowires grown on Si substrates are carried out by temperature-dependent photoluminescence (PL) and PL excitation, to evaluate effects of the shell formation on carrier recombination. The PL emission from the GaAs core is found to transform into a series of sharp PL lines upon radial growth of the GaNAs shell, pointing toward the formation of localization potentials in the core. This hampers carrier transfer at low temperatures from the core in spite of its wider bandgap. Carrier injection from the core to the optically active shell is found to become thermally activated at Tamp;gt;60 K, which implies that the localization potentials are rather shallow. (C) 2016 American Vacuum Society.

  • 33.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Dobrovolsky, Alexander
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Kuang, K. J.
    Sukrittanon, Supanee
    Tu, Charles W.
    Department of Electrical and Computer Engineering, University of California.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Defect formation and optical properties of coaxial GaP/GaNP core/shell Nanowires (invited talk)2016Conference paper (Refereed)
  • 34.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Shula
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Jansson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Ishikawa, F.
    Ehime University, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Defect formation in GaAs/GaNxAs1-x core/shell nanowires2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 20, article id 203103Article in journal (Refereed)
    Abstract [en]

    Photoluminescence and optically detected magnetic resonance (ODMR) spectroscopies are used to investigate the formation and role of defects in GaAs/GaNxAs1-x core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates. Gallium vacancies, which act as non-radiative recombination (NRR) centers, are identified by ODMR. It is shown that the defects are formed in bulk regions, i.e., not on the surface, of the GaNAs shell and that their concentration increases with increasing nitrogen content. Temperature dependent photoluminescence experiments reveal, on the other hand, suppressed thermal quenching of the near-band-edge emission with increasing [N]. This leads to the conclusion that the dominant NRR processes in the studied NWs are governed by surface defects, whereas the role of gallium vacancies in the observed thermally activated NRR is minor. Published by AIP Publishing.

  • 35.
    Chen, Weimin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Extraordinary Defect-enabled Spin Functionalities in Semiconductors (invited talk)Extraordinary Defect-enabled Spin Functionalities in Semiconductors2016In: Proc. of the 33rd Int. Conf. Phys. Semicond. (2017) in press, 2016Conference paper (Refereed)
  • 36.
    Puttisong, Yuttapoom
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Cavendish Laboratory, University of Cambridge.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Xia, Yuxin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin M.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Microscopic signature of the interfacial charge transfer states and their relevant spin-dependent processes in organic photovoltaics2016Conference paper (Refereed)
  • 37.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Ishikawa, F.
    Ehime University, Japan.
    Tu, C. W.
    University of Calif San Diego, USA.
    Novel GaNAs and GaNP-based Nanowires - Promising Materials for Optoelectronics and Photonics2016In: 2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO), IEEE , 2016, p. 38-41Conference paper (Refereed)
    Abstract [en]

    In this paper we review our recent results on optical properties of coaxial nanowires (NWs) based on dilute nitride alloys, such as GaAsN and GaNP. We show that these structures have a high structural and optical quality, and can potentially be used as polarized nano-scale light sources that emit linearly polarized light with the polarization direction perpendicular to the wire axis even in zincblende NWs of various diameters. We also demonstrate that, though the GaNxP1-x alloys have rather wide bandgap energies of 1.9 - 2.3 eV, the coaxial GaNP NWs absorb infrared light via two-step two-photon absorption.

  • 38.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Stehr, Jan Eric
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Tu, C. W.
    University of Calif La Jolla, CA USA.
    Novel GaP/GaNP core/shell nanowires for optoelectronics and photonics (invited talk)2016In: The 7th IEEE International Nanoelectronics Conference 2016, IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    GaNP-based nanowires (NWs) represent a novel material system that has a great potential in a variety of optoelectronic and photonic applications. In this paper we review our recent results showing that advantages provided by alloying with nitrogen can be realized and even further enhanced in novel coaxial GaNP NWs grown on Si substrates. Based on combined mu-photoluminescence and optically detected magnetic resonance measurements, we identify the optimum structural design of these nanowires. We also demonstrate that these novel structures have potential as nanoscale light sources of linearly polarized light.

  • 39.
    Kovalchuk, A. O.
    et al.
    National Academic Science Ukraine, Ukraine.
    Rudko, G. Yu.
    National Academic Science Ukraine, Ukraine.
    Fediv, V. I.
    Bukovinian State Medical University, Ukraine.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Phosphorescence of CdS nanoparticles in polymer matrix as an indication of host-guest interaction2016In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 177, p. 379-383Article in journal (Refereed)
    Abstract [en]

    We report on the observation of the long-lasting low-temperature photoluminescence decay in the hybrid system nano-CdS/polyvinyl alcohol with a characteristic time of about 1.7 s. The origin of the phosphorescence is ascribed to the accumulation of photo-excited excitons in the traps within the polymeric matrix with subsequent transfer of the excitation to the embedded CdS nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.

  • 40.
    Huang, Yuqing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Spin injection and detection in semiconductor nanostructures (invited talk)2016In: 7TH IEEE INTERNATIONAL NANOELECTRONICS CONFERENCE (INEC) 2016, IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    We review our recent results from optical spin orientation studies of In(Ga)As/GaAs quantum dots (QD) and QD molecular structures (QMSs), which shed light on some critical issues in spin injection and spin detection in these semiconductor nanostructures.

  • 41.
    Huang, Yuqing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Spin injection loss in self-assembled InAs/GaAs quantum dot structures from disordered barrier layers2016In: 2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO), IEEE , 2016, p. 627-629Conference paper (Refereed)
    Abstract [en]

    Semiconductor quantum dot (QD) structures are considered as promising building block for spintronic applications with the advantage of prolonged spin relaxation time owing to 0D character of confined carriers or excitons. However, feasible application is haunted by severe spin injection loss from its adjacent barrier layers and its mechanism is still not fully understood. Here, we show that exciton spin injection in self-assembled InAs/GaAs QD molecular structures (QMSs) is dominated by localized excitons confined within the QD-like regions of the wetting layer (WL) and GaAs barrier layer surrounding QD structures. The origin of spin injection loss is attribute to finite anisotropic exchange interaction (AEI) of the localized excitons subjected to asymmetric confinement potential in the injection layers. As a result, the AEI of the injected excitons and, thus, the spin injection efficiency is determined to be correlated with the overall geometric symmetry of QMSs, which hold strong influence on the confinement potential of the localized excitons in the surrounding barrier layers. Our results shed light on the microscopic origin of the spin injection loss in QD structures. More importantly, they offer a useful guideline to significantly improve spin injection efficiency by optimizing the lateral arrangement of QMSs and overcome a major challenge in the QD based spintronic device applications.

  • 42.
    Filippov, Stanislav
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Jansson, Mattias
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Stehr, Jan Eric
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O. Å.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ishikawa, Fumitaro
    Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan.
    Chen, Weimin M.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Strongly polarized quantum-dot-like light emitters embedded in GaAs/GaNAs core/shell nanowires2016In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 8, no 35, p. 15939-15947Article in journal (Refereed)
    Abstract [en]

    Recent developments in fabrication techniques and extensive investigations of the physical properties of III-V semiconductor nanowires (NWs), such as GaAs NWs, have demonstrated their potential for a multitude of advanced electronic and photonics applications. Alloying of GaAs with nitrogen can further enhance the performance and extend the device functionality via intentional defects and heterostructure engineering in GaNAs and GaAs/GaNAs coaxial NWs. In this work, it is shown that incorporation of nitrogen in GaAs NWs leads to formation of three-dimensional confining potentials caused by short-range fluctuations in the nitrogen composition, which are superimposed on long-range alloy disorder. The resulting localized states exhibit a quantum-dot like electronic structure, forming optically active states in the GaNAs shell. By directly correlating the structural and optical properties of individual NWs, it is also shown that formation of the localized states is efficient in pure zinc-blende wires and is further facilitated by structural polymorphism. The light emission from these localized states is found to be spectrally narrow (similar to 50-130 mu eV) and is highly polarized (up to 100%) with the preferable polarization direction orthogonal to the NW axis, suggesting a preferential orientation of the localization potential. These properties of self-assembled nano-emitters embedded in the GaNAs-based nanowire structures may be attractive for potential optoelectronic applications.

  • 43.
    Filippov, Stanislav
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Ishikawa, F.
    Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan.
    Chen, Weimin M
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Structural properties of GaNAs nanowires probed by micro-Raman spectroscopy2016In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 31, no 2, article id 025002Article in journal (Refereed)
    Abstract [en]

    GaNAs-based nanowires (NWs) form a novel material system of potential importance for applications in advanced optoelectronic and photonic devices, thanks to the advantages provided by band-structure engineering, one-dimensional architecture and the possibility to combine them with mainstream silicon technology. In this work we utilize the micro-Raman scattering technique to systematically study the structural properties of such GaAs/GaNAs core/shell NW structures grown by molecular beam epitaxy on a Si substrate. It is shown that the employed one-dimensional architecture allows the fabrication of a GaNAs shell with a low degree of alloy disorder and weak residual strain, at least within the studied range of nitrogen (N) compositions [N] < 0.6%. Raman scattering by the GaAs-like and GaN-like phonons is found to be enhanced when the excitation energy approaches the E + transition energy. Since this effect is found to be more pronounced for the GaN-like phonons, the involved intermediate states are concluded to be localized in proximity to N impurities, i.e. they likely represent N-related cluster states located in proximity to E + .

  • 44.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. 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.
    Svensson, Bengt
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    The zinc vacancy – donor complex: A relevant compensating center in n-type ZnO (invited talk)2016Conference paper (Refereed)
  • 45.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Svensson, B. G.
    University of Oslo, Norway.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Thermal stability of the prominent compensating (Al-Zn-V-Zn) center in ZnO2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 10, p. 105702-Article in journal (Refereed)
    Abstract [en]

    Electron paramagnetic resonance spectroscopy is used to investigate the thermal stability of the Aluminum-Zinc vacancy (Al-Zn-V-Zn) complex created in bulk single crystalline ZnO by room temperature electron irradiation with an energy of 1.2 MeV. Two different stages in the annealing process at 160 and 250 degrees C with apparent activation energies of E-A1 = 1.5 +/- 0.2 eV and E-A2 = 1.9 +/- 0.2 eV, respectively, are observed. The second stage leads to the complete annealing out of the (Al-Zn-V-Zn) complex and is accompanied by restoration of the concentration of the AlZn shallow donor centers to its initial value in as-grown (i.e., not irradiated) material. The obtained results prove that the (Al-Zn-V-Zn) complex is the dominant acceptor responsible for compensation of n-type-dopants in the studied Al-containing ZnO samples. (C) 2016 AIP Publishing LLC.

  • 46.
    Huang, Yuqing Q.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    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.
    Understanding and optimizing spin injection in self-assembled InAs/GaAs quantum-dot molecular structures2016In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 9, no 3, p. 602-611Article in journal (Refereed)
    Abstract [en]

    Semiconductor quantum-dot (QD) structures are promising for spintronic applications owing to strong quenching of spin relaxation processes promoted by carrier and excitons motions. Unfortunately, spin injection efficiency in such nanostructures remains very low and the exact physical mechanism for the spin loss is still not fully understood. Here, we show that exciton spin injection in self-assembled InAs/GaAs QDs and quantum-dot molecular structures (QMSs) is dominated by localized excitons confined within the QD-like regions of the wetting layer (WL) and GaAs barrier layer immediately surrounding QDs and QMSs that in fact lack the commonly believed 2D and 3D character with an extended wavefunction. We identify the microscopic origin of the observed severe spin loss during spin injection as being due to a sizable anisotropic exchange interaction (AEI) of the localized excitons in the WL and GaAs barrier layer, which has so far been overlooked. We find that the AEI of the injected excitons and thus the efficiency of the spin injection processes are correlated with the overall geometric symmetry of the QMSs, as the latter largely defines the anisotropy of the confinement potential of the localized excitons in the surrounding WL and GaAs barrier. These results pave the way for a better understanding of spin injection processes and the microscopic origin of spin loss in QD structures, which in turn provides a useful guideline to significantly improve spin injection efficiency by optimizing the lateral arrangement of the QMSs thereby overcoming a major bottleneck in spintronic device applications utilizing semiconductor QDs.

  • 47.
    Stehr, Jan Eric
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Reddy, N. K.
    Humboldt University, Institute of Chemistry, Berlin, Germany .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, CA, USA .
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Unintentional nitrogen incorporation in ZnO nanowires detected by electron paramagnetic resonance spectroscopy2016In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 13, no 7-9, p. 572-575Article in journal (Refereed)
    Abstract [en]

    Unintentional incorporation of nitrogen in ZnO nanowires (NWs) grown by rapid thermal chemical vapor deposition is unambiguously proven by electron paramagnetic resonance spectroscopy. The nitrogen dopants are suggested to be provided from contaminations in the source gases. The majority of incorporated nitrogen atoms are concluded to reside at oxygen sites, i.e. in the atomic configuration of nitrogen substituting for oxygen (NO). The NO centers are suggested to be located in proximity to the NW surface, based on their reduced optical ionization energy as compared with that in a bulk material. This implies that the defect formation energy at the NW surface could be lower than its bulk value, consistent with previous theoretical predictions. The obtained results underline that nitrogen can be easily incorporated in ZnO nanostructures which may be of advantage for realizing p-type conducting ZnO via N doping. On the other hand, the awareness of this process can help to prevent such unintentional doping in structures with desired n-type conductivity.

  • 48.
    Filippov, Stanislav
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Ishikawa, Fumitaro
    Graduate School of Science and Engineering, Ehime University, 790-8577 Matsuyama, Japan.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Faculty of Science & Engineering.
    Characterization of GaAs/GaNAs core/shell nanowires by means of Raman scattering spectroscopy2015In: Abstract Book, 2015, p. IP2.27-Conference paper (Refereed)
  • 49.
    Dagnelund, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Huang, Yuqing
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Yonezu, H.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Japan .
    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.
    Dual-wavelength excited photoluminescence spectroscopy of deep-level hole traps in Ga(In)NP2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, p. 015701-Article in journal (Refereed)
    Abstract [en]

    By employing photoluminescence(PL) spectroscopy under dual-wavelength optical excitation, we uncover the presence of deep-level hole traps in Ga(In)NP alloys grown by molecular beam epitaxy(MBE). The energy level positions of the traps are determined to be at 0.56 eV and 0.78 eV above the top of the valance band. We show that photo-excitation of the holes from the traps, by a secondary light source with a photonenergy below the bandgapenergy, can lead to a strong enhancement (up to 25%) of the PL emissions from the alloys under a primary optical excitation above the bandgapenergy. We further demonstrate that the same hole traps can be found in various MBE-grown Ga(In)NP alloys, regardless of their growth temperatures, chemical compositions, and strain. The extent of the PL enhancement induced by the hole de-trapping is shown to vary between different alloys, however, likely reflecting their different trap concentrations. The absence of theses traps in the GaNP alloy grown by vapor phase epitaxy suggests that their incorporation could be associated with a contaminant accompanied by the N plasma source employed in the MBEgrowth, possibly a Cu impurity.

  • 50.
    Dobrovolskiy, Alexander
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Persson, Per O. Å
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sukrittanon, Supanee
    Graduate Program of Materials Science and Engineering, University of California, La Jolla, California 92093, United States.
    Kuang, Yanjin
    Department of Physics, University of California, La Jolla, California 92093, United States.
    Tu, CHarles W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California 92093, United States.
    Chen, Weimin
    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.
    Effects of Polytypism on Optical Properties and Band Structure ofIndividual Ga(N)P Nanowires from Correlative Spatially Resolved Structural and Optical Studies2015In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 15, no 6, p. 4052-4058Article in journal (Refereed)
    Abstract [en]

    III-V semiconductor nanowires (NWs) have gained significant interest as building blocks in novel nanoscale devices. The one-dimensional (1D) nanostructure architecture allows one to extend band structure engineering beyond quantum confinement effects by utilizing formation of different crystal phases that are thermodynamically unfavorable in bulk materials. It is therefore of crucial importance to understand the influence of variations in the NWs crystal structure on their fundamental physical properties. In this work we investigate effects of structural polytypism on the optical properties of gallium phosphide and GaP/GaNP core/shell NW structures by a correlative investigation on the structural and optical properties of individual NWs. The former is monitored by transmission electron microscopy, whereas the latter is studied via cathodoluminescence (CL) mapping. It is found that structural defects, such as rotational twins in zinc blende (ZB) GaNP, have detrimental effects on light emission intensity at low temperatures by promoting nonradiative recombination processes. On the other hand, formation of the wurtzite (WZ) phase does not notably affect the CL intensity neither in GaP nor in the GaNP alloy. This suggests that zone folding in WZ GaP does not enhance its radiative efficiency, consistent with theoretical predictions. We also show that the change in the lattice structure have negligible effects on the bandgap energies of the GaNP alloys, at least within the range of the investigated nitrogen compositions of <2%. Both WZ and ZB GaNP are found to have a significantly higher efficiency of radiative recombination as compared with that in parental GaP, promising for potential applications of GaNP NWs as efficient nanoscale light emitters within the desirable amber-red spectral range.

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