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  • 251.
    Murayama, A.
    et al.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Furuta, T.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Hyomi, K.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Souma, I.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Dagnelund, Daniel
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots of CdSe coupled with a diluted magnetic semiconductor layer of Zn0.80 Mn0.20 Se2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 19, p. 195308-Article in journal (Refereed)
    Abstract [en]

    We study the dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of Zn0.80 Mn0.20 Se, where spin-polarized excitons can be injected from the DMS into the QDs. The degree of circular polarization P of excitonic photoluminescence (PL) at 5 T in the coupled QDs exhibits a rapid increase with increasing delay time, up to +0.3 at 25 ps after the pulse excitation of the DMS by a linearly polarized light. This development of a positive P value directly reflects the spin-injection dynamics from the DMS, since the intrinsic polarization of the QD excitons due to Zeeman splitting is P∼-0.1 when only the QDs are selectively excited. The P value gradually decays with time after reaching its maximum, as a result of the exciton-spin relaxation with a time constant of 800 ps in the QDs. Time-resolved circularly polarized PL spectra immediately after the pulse excitation directly show the exciton-energy dependence of the spin-injection dynamics in the QD ensemble, where two-dimensional-like QDs with higher exciton energies show higher receptivity to the spin-polarized excitons than three-dimensional-like dots with lower exciton energies. A rate equation analysis reveals all time constants responsible for the spin-injection dynamics. We deduce a time constant of 10 ps for the spin injection. The spin-injection efficiency of 0.94 is also obtained, which corresponds to the ratio between the number of the spin-polarized excitons responsible for the rise of the positive P value in the QD emission and the total number of the excitons injected from the DMS. Moreover, we observe that interdot exciton transfer significantly affects the P value within the QD emission band after the fast spin injection, in addition to the spin relaxation within the QDs. © 2007 The American Physical Society.

  • 252.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Wang, Xingjun
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Vorona, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Utsumi, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Furukawa, Y.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Moon, S.
    Wakahara, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Yonezu, H.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Effect of growth conditions on grown-in defects in Ga(In)NP alloys2007Conference paper (Other academic)
  • 253.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Pearton, S. J.
    Bihler, C.
    Brandt, M. S.
    Hong, Y. G.
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, USA.
    Efficiency of hydrogen passivation of nitrogen in GaAsN and GaNP alloys2007Conference paper (Other academic)
  • 254.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Murayama, A.
    Furuta, T.
    Hyomi, K.
    Souma, I.
    Oka, Y.
    Exciton spin injection from a ZnCdMnSe diluted magnetic quantum well to self-assembled CdSe quantum dots2007In: Fourth International School and Conference on Spintronics and Quantum Information Technology Spintech IV,2007, 2007, p. 156-Conference paper (Other academic)
  • 255. Pearton, S. J.
    et al.
    Norton, D. P.
    Ivill, M. P.
    Hebard, A. F.
    Zavada, J. M.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Ferromagnetism in transition-metal doped ZnO2007In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 36, no 4, p. 462-471Article, review/survey (Refereed)
    Abstract [en]

    ZnO is an attractive candidate for spintronics studies because of its potential for exhibiting high Curie temperatures and the relative lack of ferromagnetic second phases in the material. In this paper, we review experimental results on transition-metal (TM) doping of ZnO and the current state of theories for ferromagnetism. It is important to re-examine some of the earlier concepts for spintronics devices, such as the spin field-effect transistor, to account for the presence of the strong magnetic field that has deleterious effects. In some of these cases, the spin device appears to have no advantage relative to the conventional charge-control electronic analog. We have been unable to detect optical spin polarization in ZnO.

  • 256.
    Wang, Xingjun
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Pan, C. J.
    Tu, C. W.
    Grown-in defects in molecular beam epitaxial ZnO2007In: XVI International Materials Research Congress,2007, 2007Conference paper (Other academic)
  • 257.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Izadifard, Morteza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Pearton, S.J.
    Bihler, C.
    Brandt, M.S.
    Hong, Y.G.
    Tu, C.W.
    Hydrogen passivation of nitrogen in GaNAs and GaNP alloys: How many H atoms are required for each N atom?2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 2, p. 021920-Article in journal (Refereed)
    Abstract [en]

    Secondary ion mass spectrometry and photoluminescence are employed to evaluate the origin and efficiency of hydrogen passivation of nitrogen in GaNAs and GaNP. The hydrogen profiles are found to closely follow the N distributions, providing unambiguous evidence for their preferential binding as the dominant mechanism for neutralization of N-induced modifications in the electronic structure of the materials. Though the exact number of H atoms involved in passivation may depend on the conditions of the H treatment and the host matrixes, it is generally found that more than three H atoms are required to bind to a N atom to achieve full passivation for both alloys. © 2007 American Institute of Physics.

  • 258.
    Vorona, Igor
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Mchedlidze, T.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Dagnelund, Daniel
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Köhler, K.
    Fraunhofer‐Institut für Angewandte Festkörperphysik, Freiburg, Germany .
    Identification of point defects in Ga(Al)NAs alloys2007In: AIP Conference Proceedings / Volume 893: PHYSICS OF SEMICONDUCTORS: 28th International Conference on the Physics of Semiconductors - ICPS 2006, American Institute of Physics (AIP), 2007, p. 227-228Conference paper (Other academic)
    Abstract [en]

    By employing the optically detected magnetic resonance (ODMR) technique, two differentGai defects, namely Gai-A and Gai-B, are found and identifiedin the investigated Ga(Al)NAs epilayers grown on GaAs substrates bymolecular-beam epitaxy (MBE). This finding shows that Ga interstitials arecommon intrinsic defects in various dilute nitrides. In addition tothe Gai-related defects, “middle line” ODMR signals were observed ataround g=2 and are suggested to arise from superposition ofa defect with a single ODMR line and a defectwith an unresolved HF structure. All defects studied are shownto act as non-radiative recombination centers, and are therefore harmfulto performance of potential light-emitting devices based on the alloys.©2007 American Institute of Physics

  • 259.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Oka, Y.
    Abernathy, C. R.
    Pearton, S. J.
    Magneto-optical spectroscopy of spin injection and spin relaxation in ZnMnSe/ZnCdSe and GaMnN/InGaN spin light-emitting structures2007In: 2006 E-MRS Fall Meeting, 2007, Vol. 204, no 1, p. 159-173Conference paper (Refereed)
    Abstract [en]

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

  • 260.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rawal, S.
    Norton, D.P.
    Pearton, S.J.
    Osinsky, A.
    Dong, J.W.
    Mechanism for radiative recombination in ZnCdO alloys2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 26Article in journal (Refereed)
    Abstract [en]

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

  • 261. Wang, S.M.
    et al.
    Tångring, I.
    Gu, Q.F.
    Sadeghi, M.
    Larsson, A.
    Wang, X.D.
    Ma, C.H.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Metamorphic InGaAs quantum wells for light emission at 1.3-1.6 μm2007In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 10, p. 4348-4351Article in journal (Refereed)
    Abstract [en]

    Metamorphic InGaAs quantum well structures grown on GaAs reveal strong light emission at 1.3-1.6 μm, smooth surface with an average roughness below 2 nm and good rectifying I-V characteristics. Dark line defects are found in the QW. Post growth thermal annealing further improves the luminescence efficiency but does not remove those dark line defects. Some challenges of epitaxial growth using this method for laser applications are discussed. © 2006 Elsevier B.V. All rights reserved.

  • 262.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Tu, C.W.
    Optical and electronic properties of GaInNP alloys - a new material system for lattice matching to GaAs2007In: EMRS-2007 Spring Meeting,2007, 2007Conference paper (Other academic)
  • 263.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Tu, C. W.
    Optical characterization of novel GaInNP alloys2007In: XVI International Materials Research Congress,2007, 2007Conference paper (Other academic)
  • 264.
    Wang, Xiangjun
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Pan, C.J.
    Department of Electrical and Computer Engineering, University of California, La Jolla, United States, Optical Sciences Center, National Central University, Jhongli, Taoyuan 32001, Taiwan.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, United States.
    Optical characterization studies of grown-in defects in ZnO epilayers grown by molecular beam epitaxy2007In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 401-402, p. 413-416Article in journal (Refereed)
    Abstract [en]

    Defect formation in ZnO epilayers grown by molecular beam epitaxy (MBE) is studied by employing optical characterization techniques such as photoluminescence (PL) and optically detected magnetic resonance (ODMR). Excess of oxygen during the growth was found to cause an appearance of the PL peak at around 3.338 eV, which indicates that the corresponding defects are predominantly formed in O-rich ZnO. On the other hand, non-stoichiometry during the growth was singled out as the main factor facilitating formation of defects involved in the yellow PL emission band peaking at around 2.17 eV. Several magnetic-resonance active defects are revealed via monitoring this emission and their magnetic-resonance signatures are obtained. © 2007 Elsevier B.V. All rights reserved.

  • 265.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Vorona, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Wang, X
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Geelhaar, L.
    Infineon Technologies, Corporate Research, Munich, Germany .
    Riechert, H.
    Infineon Technologies, Corporate Research, Munich, Germany .
    Optically detected cyclotron resonance studies of InGaNAs/GaAs structures2007In: Physics of semiconductors : 28th International Conference on the Physics of Semiconductors, ICPS 2006, Vienna, Austria, 24-28 July 2006, American Institute of Physics (AIP), 2007, p. 383-384Conference paper (Other academic)
    Abstract [en]

    We report on our recent results from a systematic study of layered structures containing an InGaNAs/GaAs quantum well (QW), by the optically detected cyclotron resonance (ODCR) technique. By monitoring photoluminescence (PL) emissions from various layers the predominant ODCR peak is shown to be related to carriers with a 2D character and an effective mass of 0.51 me. The responsible carriers are ascribed to be electrons in GaAs/AlAs superlattices (SL) that are employed in the laser structures to prevent carrier leak by sandwiching the InGaNAs/GaAs QW. This conclusion is based on the following observations: (a) the ODCR peak is only observed in the structures containing the SL; (b) the effective mass value determined by the ODCR peak is independent of In and N compositions; (c) the same ODCR peak is also observed by monitoring PL from the SL. Unfortunately no ODCR signal related to InGaNAs was observed

  • 266.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Vorona, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Wang, Xingjun
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Geelhaar, L.
    Riechert, H.
    Optically detected cyclotron resonance studies of InxGa1-xNyAs1-y/GaAs quantum wells sandwiched between type-II AlAs/GaAs superlattices.2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, p. 073705-Article in journal (Refereed)
    Abstract [en]

      We report on our results from a systematic study of layered structures containing an InGaNAs/GaAs single quantum well (SQW) enclosed between staggered type II AlAs/GaAs superlattices (SL), by the photoluminescence (PL) and optically detected cyclotron resonance (ODCR) techniques. Besides the ODCR signal known to originate from electrons in GaAs, the predominant ODCR peak is shown to be related to carriers with a two-dimensional character and a cyclotron resonance effective mass of m*[approximate](0.51-0.56)m0. The responsible carriers are ascribed to electrons on the ellipsoidal equienergy surface at the AlAs X point of the Brillouin zone within the SL, based on results from angular and spectral dependences of the ODCR signal. No ODCR signal related to the InGaNAs SQW was detected, presumably due to low carrier mobility despite the high optical quality. Multiple absorption of photons with energy below the band gap energy of the SL and the GaAs barriers was observed, which bears implication on the efficiency of light-emitting devices based on these structures.

  • 267.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Rawal, S.
    Norton, D.P.
    Pearton, S.J.
    Osinsky, A.
    Dong, J.W.
    Origin of near-band-edge emission in ZnCdO alloys2007In: 2007 MRS Fall Meeting,2007, 2007, p. 319-Conference paper (Other academic)
  • 268.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan.
    Abernathy, C.R.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Pearton, S.J.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Prospects of potential semiconductor spin detectors2007In: Advances in Nanomaterials and Processing, Pts 1 and 2 / [ed] Byung Tae Ahn, Hyeongtag Jeon, Bo Young Hur, Kibae Kim and Jong Wan Park, Trans Tech Publications Inc., 2007, p. 839-842Conference paper (Refereed)
    Abstract [en]

    We review our recent experimental findings by optical orientation spectroscopy that show efficient spin relaxation within semiconductor spin detectors to be an important factor limiting efficiency of spin injection in spin light-emitting structures based on ZnCdSe/ZnMnSe and InGaN/GaMnN. We provide evidence for the physical mechanism responsible for the observed efficient spin relaxation that accompanies momentum and energy relaxation of excitons/carriers. These findings call for increasing efforts in suppressing spin relaxation in spin detectors.

  • 269.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Izadifard, Morteza
    Physics Department, Shahrood University of Technology, Shahrood, Iran .
    Hong, Y.G.
    Department of Electrical and Computer Engineering, University of California, La Jolla, CA, USA.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, CA, USA.
    Role of nitrogen in photoluminescence up-conversion in GaInNP/GaAs heterostructures2007In: AIP Conference Proceedings / Volume 893 / [ed] Wolfgang Jantsch, Friedrich Schaffler, American Institute of Physics (AIP), 2007, p. 381-382Conference paper (Other academic)
    Abstract [en]

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

  • 270.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Murayama, A.
    Oka, Y.
    Spin dynamics and spin injection in II-VI semiconductors and nanostructures2007In: 8th Japan-Sweden QNANO Workshop,2007, 2007Conference paper (Other academic)
  • 271.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Murayama, A.
    Oka, Y.
    Pearton, S.J.
    Norton, D.P.
    Abernathy, C.R.
    Osinsky, A.
    Dong, J.W.
    Spin dynamics in wide bandgap semiconductors and nanostructures - potential spintronic materials2007In: XVI International Materials Research Congress,2007, 2007Conference paper (Other academic)
    Abstract [en]

      

  • 272.
    Koyama, T.
    et al.
    MRAM, Tohoku University, Sendai, Japan.
    Nishibayashi, K.
    MRAM, Tohoku University, Sendai, Japan.
    Murayama, A.
    MRAM, Tohoku University, Sendai, Japan.
    Oka, Y.
    MRAM, Tohoku University, Sendai, Japan.
    Toropov, A.A.
    Ioffe Physico‐Technical Institute, Russian Academy of Sciences, St. Petersburg, Russia .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Spin dynamics of type-II excitons in diluted magnetic double quantum wells2007In: 28th Int. Conf. on the Physics of Semiconductors,2006, American Institute of Physics (AIP), 2007, p. 465-Conference paper (Other academic)
    Abstract [en]

    Dynamical properties of the electron and hole spins are demonstrated indouble quantum wells composed of diluted magnetic and nonmagnetic semiconductors.Excitonic photoluminescence of the type-II transition appears for the lower-lyingdown-spin level of the exciton in magnetic field. A type-Iexciton transition is also observed for the opposite up-spin excitonstate. The result shows the spatial spin separation and thespin-injection dynamics for the heavy-hole spin states in the doublequantum wells. ©2007 American Institute of Physics

  • 273.
    Pearton, Stephen J.
    et al.
    Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Norton, D.P.
    Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Ivill, M.P.
    Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Hebard, A.F.
    Physics, University of Florida, Gainesville, FL, USA.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Zavada, J.M.
    Electronics Division, Army Research Office, NC, USA.
    Transition Metal Doped ZnO for Spintronics2007In: MRS Proceedings 2007 vol. 999, Warrendale, PA: Materials Research Society , 2007, p. 0999-K03-K04Conference paper (Other academic)
    Abstract [en]

    ZnO is a very promising material for spintronics applications, with many groups reporting room temperature ferromagnetism in films doped with transition metals during growth or by ion implantation. In films doped with Mn during PLD, we find an inverse correlation between magnetization and electron density as controlled by Sn doping. The saturation magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature, suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn and factors such as crystalline quality and residual defects play a role. Plausible mechanisms for the ferromagnetism include the bound magnetic polaron model or exchange is mediated by carriers in a spin-spilt impurity band derived from extended donor orbitals. Spin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors.

  • 274.
    Pearton, S.J.
    et al.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, United States.
    Norton, D.P.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, United States.
    Ivill, M.P.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, United States.
    Hebard, A.F.
    Department of Physics, University of Florida, Gainesville, FL 32611, United States.
    Zavada, J.M.
    Army Research Office, Research Triangle Park, NC 27709, United States.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina A.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    ZnO doped with transition metal ions2007In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 54, no 5, p. 1040-1048Article in journal (Refereed)
    Abstract [en]

    Spin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. In this paper, we review the experimental results on transition metal doping of ZnO and show that the material can be made with a single phase at high levels of Co incorporation (~ 15 at.%) and exhibits the anomalous Hall effect. ZnO is expected to be one of the most promising materials for room-temperature polarized light emission, but to date, we have been unable to detect the optical spin polarization in ZnO. The short spin relaxation time observed likely results from the Rashba effect. Possible solutions involve either cubic phase ZnO or the use of additional stressor layers to create a larger spin splitting in order to get a polarized light emission from these structures or to look at alternative semiconductors and fresh device approaches. © 2007 IEEE.

  • 275.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Murayama, A.
    Oka, Y.
    Norton, D.P.
    Pearton, S.J.
    Osinsky, A.
    Dong, J.W.
    ZnO for spintronics: some critical issues2007In: Abstract Book of the 2007 MRS Fall Meeting, 2007, p. 326-Conference paper (Other academic)
  • 276.
    Wang, Xingjun
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Izadifard, M.
    Department of Physics, Shahrood University of Technology, Shahrood, Iran .
    Rawal, S.
    Department of Materials Science and Engineering, University of Florida, Gainesville, Florida.
    Norton, D.P.
    Department of Materials Science and Engineering, University of Florida, Gainesville, Florida.
    Pearton, S.J.
    Department of Materials Science and Engineering, University of Florida, Gainesville, Florida.
    Osinsky, A.
    SVT Associates, Eden Prairie, Minnesota.
    Dong, J.W.
    SVT Associates, Eden Prairie, Minnesota.
    Dabiran, A.
    SVT Associates, Eden Prairie, Minnesota.
    Band gap properties of Zn1−xCdxO alloys grown by molecular-beam epitaxy2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, p. 151909-Article in journal (Refereed)
    Abstract [en]

    Optical absorption and reflectance measurements are performed to evaluate compositional and temperature dependences of band gap energies of Zn1−xCdxO alloys grown by molecular-beam epitaxy. The compositional dependence of the band gap energy, determined by taking into account excitonic contributions, is shown to follow the trend Eg(x) = 3.37−2.82x+0.95x2. Incorporation of Cd was also shown to somewhat slow down thermal variation of the band gap energies, beneficial for future device applications.

  • 277.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Vorona, I.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Izadifard, M.
    Hong, Y.G.
    Tu, C.W.
    Band line-up in novel GaInNP/GaAs heterostructures2006In: IUMRS 2006 International Conference in Asia,2006, 2006, p. 8-O-1-Conference paper (Other academic)
  • 278.
    Toropov, A.A.
    et al.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg, Russia.
    Terent'ev, Ya.V.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg, Russia.
    Sorokin, S.V.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg, Russia.
    Ivanov, S.V.
    Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg, Russia.
    Koyama, T.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Nishibayashi, K.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Murayama, A.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai , Japan.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Density-dependent dynamics of exciton magnetic polarons in ZnMnSe/ZnSSe type-II quantum wells2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 24, p. 245335-Article in journal (Refereed)
    Abstract [en]

    We report on time-resolved photoluminescence studies of exciton dynamics in a ZnMnSe/ZnSSe type-II quantum well. Strong separation of the electrons, confined to the nonmagnetic semiconductor ZnSSe, and holes, confined to the diluted magnetic semiconductor ZnMnSe, results in an exciton lifetime exceeding 3 ns. Two excitonic emission lines are observed in this structure at low temperatures. The lower-energy line was associated with the formation of an exciton magnetic polaron (EMP), whereas the higher-energy line was attributed to the emission of nonmagnetically localized excitons. The intensity of the EMP line was found to saturate at a relatively low density of photoexcited carriers well below the exciton Mott density. This behavior evidences a limited density of sites where the hole localization radius is small enough to ensure the fast formation of EMP's with a noticeable binding energy. © 2006 The American Physical Society.

  • 279.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Mchedlidze, T.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Utsumi, A.
    Furukawa, Y.
    Moon, S.
    Wakahara, A.
    Yonezu, H.
    Effect of nitrogen ion bombardment on defect formation and luminescence efficiency of GaNP epilayers grown by molecular-beam epitaxy2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 10, p. 101904-Article in journal (Refereed)
    Abstract [en]

    Radiative efficiency of GaNP epilayers grown on GaP substrates by solid-source molecular beam epitaxy is significantly improved by reduced nitrogen ion bombardment during the growth. Based on the results of temperature-dependent photoluminescence (PL) and optically detected magnetic resonance studies (ODMR), the observed improvements are attributed to reduced formation of defects, such as a Ga interstitial related defect and an unidentified defect revealed by ODMR. We demonstrate that these defects act as competing recombination centers, which promote thermal quenching of the PL intensity and result in a substantial (34×) decrease in room-temperature PL intensity. © 2006 American Institute of Physics.

  • 280.
    Norton, D.P.
    et al.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Pearton, S.J.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Zavada, J.M.
    Army Research Office, NC, USA.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ferromagnetism in ZnO Doped with Transition Metal Ions2006In: ZnO Bulk, Thin Films and Nanostructures: Processing, Properties and Applications / [ed] Chennupati Jagadish, Stephen J. Pearton, Oxford: Elsevier , 2006, 1, p. 555-576Chapter in book (Other academic)
    Abstract [en]

    With an in-depth exploration of the following topics, this book covers the broad uses of zinc oxide within the fields of materials science and engineering: - Recent advances in bulk , thin film and nanowire growth of ZnO (including MBE, MOCVD and PLD), - The characterization of the resulting material (including the related ternary systems ZgMgO and ZnCdO), - Improvements in device processing modules (including ion implantation for doping and isolation ,Ohmic and Schottky contacts , wet and dry etching), - The role of impurities and defects on materials properties - Applications of ZnO in UV light emitters/detectors, gas, biological and chemical-sensing, transparent electronics, spintronics and thin film

  • 281.
    Vorona, Igor
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Utsumi, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Furukawa, Y.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Moon, S.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Wakahara, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Yonezu, H.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Intrinsic paramagnetic defects in GaNP alloys grown on silicon2006In: 210th ECS Meeting Volume 3, Issue 5: State-of-the-Art Program on Compound Semiconductors 45 (SOTAPOCS 45) -and- Wide Bandgap Semiconductor Materials and Devices 7 / [ed] F. Ren, J. Bardwell, P. Chang, W. Johnson, P. Shen, E. Stokes, Electrochemical Society, 2006, Vol. 3, p. 231-236Conference paper (Other academic)
    Abstract [en]

    Wepresent our recent results of grown-in defects in the GaNPalloy lattice matched to Si, by optically detected magnetic resonance.One of the defects was identified as the Gai-B complex,commonly formed in dilute nitrides. The remaining defects are suggestedto be probably related to intrinsic defects as well.

  • 282. Tu, CW
    et al.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Hwang, JS
    Material properties of dilute nitrides: Ga(In)NAs and Ga(In)NP2006Conference paper (Refereed)
    Abstract [en]

    The dramatic effect of incorporating a small amount of nitrogen into Ga(In)As and Ga(In)P on their materials properties, such as effective mass, band alignment, and band structure, is summarized. ©2005 Elsevier B.V. All rights reserved.

  • 283.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Izadifard, M.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hong, Y.G.
    Tu, C.W.
    Modeling of band gap properties of GaInNP alloys lattice matched to GaAs2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 3, p. 31907-Article in journal (Refereed)
    Abstract [en]

    Compositional and temperature dependences of the band gap energies of GaInNP alloys, which are lattice matched to GaAs, are determined and modeled by a band anticrossing (BAC) interaction between the localized state of the isolated NP and extended host states. The BAC parameters are deduced as EN =2.1±0.1 eV and CMN =1.7±0.2 eV. The low value of the coupling parameter CMN implies weaker coupling of the N level with the host matrix, presumably due to short range ordering effects, similar to the case of GaInNAs alloys with a high In content. The obtained information is important for future modeling of the electronic structure of the alloys. © 2006 American Institute of Physics.

  • 284.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Izadifard, M.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Xin, H.P.
    Tu, C.W.
    On a possible origin of the 2.87 eV optical transition in GaNP2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 2, p. 449-457Article in journal (Refereed)
    Abstract [en]

    Temperature dependent photoluminescence excitation spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered for the GaNxP1-x alloys. Whereas the appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with the N content in the alloys. This questions the possible association of this feature with an N-related localized state. On the basis of the results of temperature dependent measurements, it is concluded that the state involved has a non-Γ character. Excitation of the known N-related localized states via this state is found to be non-selective, unlike that between the N-related centres. The observed properties are shown to be barely consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the '2.87 eV' state as being due to either a t 2 component of the X3c (or L1c) CBM or a level arising from a complex of N and H (in some form) are also discussed. © 2006 IOP Publishing Ltd.

  • 285.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Wang, Xingjun
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Izadifard, M.
    Department of Physics, Shahrood University of Technology, Shahrood, Iran.
    Norton, D.P.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Pearton, S.J.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Osinsky, A.
    SVT Associates, Eden Prairie, MN, USA.
    Dong, J.W.
    SVT Associates, Eden Prairie, MN, USA.
    Dabiran, A.
    SVT Associates, Eden Prairie, MN, USA.
    Optical characterization of Zn(1-x)Cd(x)O alloys grown by molecular-beam epitaxy2006In: 210th ECS Meeting Volume 3, Issue 5: State-of-the-Art Program on Compound Semiconductors 45 (SOTAPOCS 45) -and- Wide Bandgap Semiconductor Materials and Devices 7 / [ed] F. Ren, J. Bardwell, P. Chang, W. Johnson, P. Shen, E. Stokes, The Electrochemical Society , 2006, Vol. 3, p. 391-398Conference paper (Other academic)
    Abstract [en]

    We have carried out comprehensive optical studies to evaluate structural and bandgap properties of Zn1-xCdxO alloys with x{less than or equalto}0.17 grown by molecular beam epitaxy. High crystalline quality ofthe alloys was concluded from cathodoluminescence measurements. Based on absorptionand reflectance measurements, the compositional dependence of the bandgap energyof ZnCdO, estimated without taking into account excitonic effects, wasfound to follow the trend Eg(x)=3.28-2.23x+0.45x2. Degradation in the alloyquality due to possible phase separation was found to causedeviations from this trend, evident from a more rapid redshift of the absorption edge. Effects of Cd incorporation onthe variation of the bandgap energies with temperature are alsodiscussed.

  • 286.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Ivill, M.P.
    Pate, R.
    Norton, D.P.
    Pearton, S.J.
    Dong, J.W.
    Osinsky, A.
    Hertog, B.
    Dabiran, A.M.
    Chow, P.P.
    Optical characterization of ZnMnO-based dilute magnetic semiconductor structures2006In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 24, no 1, p. 259-262Article in journal (Refereed)
    Abstract [en]

    n -type ZnMnO spin injection layers were grown by pulsed laser deposition on top of n-ZnMgOZnOp-AlGaNp-GaN hybrid spin light-emitting diode (LED) structures synthesized by molecular-beam epitaxy. Both the ZnMnOZnMgOZnOAlGaNGaN structures and control ZnMnO samples show no or very low (up to 10% at the lowest temperatures) optical (spin) polarization at zero field or 5 T, respectively. This indicates difficulties in generating spin polarization by optical spin orientation or possible efficient spin losses. The results are similar to those found earlier for GaMnNInGaNAlGaN spin-LED structures and indicate that these wide-band-gap dilute magnetic semiconductors with weak spin-orbit interaction and hexagonal symmetry are not attractive for spin-LED applications. © 2006 American Vacuum Society.

  • 287.
    Vorona, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Mchedlidze, T.
    Dagnelund, Daniel
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Köhler, K.
    Fraunhofer-Institut für Angewandte Festkörperphysik, Freiburg, Germany.
    Optically detected magnetic resonance studies of point defects in Ga(Al)Nas2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 12, p. 125204-Article in journal (Refereed)
    Abstract [en]

    An optically detected magnetic resonance (ODMR) study of Ga(Al)NAs alloys grown by molecular beam epitaxy on GaAs substrates is presented. A number of grown-in defects were observed which act as nonradiative recombination centers. A detailed analysis of experimental data using a spin Hamiltonian leads to the identification of two Gai defects. A comparison with similar defects in other phosphide-based diluted nitride III-V compounds, such as GaAlNP and GaInNP, allows us to obtain additional information about the nearest surrounding of the defects. A discussion of possible models for other defects observed in the experiments is also presented. © 2006 The American Physical Society.

  • 288.
    Izadifard, Morteza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hong, Y.G.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA.
    Photoluminescence upconversion in GaInNP/GaAs heterostructures grown by gas source molecular beam epitaxy2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, no 7, p. 073515-Article in journal (Refereed)
    Abstract [en]

    Properties of photoluminescence (PL) upconversion (PLU) in GaInNP/GaAs heterostructures are studied in detail by employing a number of optical spectroscopies. Based on excitation power dependent and temperature dependent PL measurements, the upconverted PL from GaInNP under optical excitation below its band gap is attributed to radiative transitions involving spatially separated localized electron-hole pairs, which is of a similar origin as the near-band-gap emission detected under optical excitation above the GaInNP band gap. The PLU process is shown to be largely promoted by increasing N content in the GaInNP alloys, due to a N-induced change in the band alignment at the GaInNP/GaAs heterointerface from the type I in the N-free structure to the type II in the samples with N compositions exceeding 0.5%. A possible mechanism for the energy upconversion is discussed in terms of two-step two-photon absorption. The photon recycling effect is shown to be important for the structures with N = 1%.

  • 289.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Tu, CW
    Yonezu, H
    Point defects in dilute nitride III-N-As and III-N-P2006Conference paper (Refereed)
    Abstract [en]

    We provide a brief review of our recent results from optically detected magnetic resonance studies of grown-in non-radiative defects in two most important dilute nitride system s-Ga(In)NAs grown on GaAs substrates and Ga(Al,In)NP grown on Si and GaP substrates. These results have led to the identification of defect complexes in the alloys, involving intrinsic defects such as As-Ga, antisites and Ga-i self-interstitials. They have also shed light on formation mechanisms of the defects and on their role in non-radiative carrier recombination that is harmful to the performance of potential optoelectronic and photonic devices based on these dilute nitrides. (c) 2005 Elsevier B.V. All rights reserved.

  • 290.
    Izadifard, Morteza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hong, Y.G.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California.
    Radiative recombination of GaInNP alloys lattice matched to GaAs2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 1, p. 011919-Article in journal (Refereed)
    Abstract [en]

    Cw- and time-resolved photoluminescence (PL) spectroscopy is employed to evaluate dominant mechanisms for light emission in GayIn1−yNxP1−x alloys grown by gas source molecular-beam epitaxy on GaAs substrates. Different from other direct band gap dilute nitrides, the low temperature PL emission was shown to be largely attributed to radiative transitions involving spatially separated localized electron-hole pairs. The observed charge separation is tentatively attributed to the long range CuPt ordering promoted by the presence of nitrogen.

  • 291.
    Vorona, Igor
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Mchedlidze, T
    Izadifard, Morteza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Hong, YG
    Tu, CW
    Signatures of grown-in defects in GaInNP alloys grown on a GaAs substrate from magnetic resonance studies2006In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, p. 571-574Article in journal (Refereed)
    Abstract [en]

    Three grown-in defects acting as centers of non-radiative recombination (NR) were detected in GaInNP alloys grown on a GaAs substrate using the optically detected magnetic resonance (ODMR) technique. Among them, one was proposed to be either a Ga-i-related defect or an AS(Ga)-related defect, from the resolved four-line hyperfine structure. The former model was concluded to be more favorable by weighing physical properties of the two defects, e.g. the likelihood for their presence in the studied structures, their spatial location, g-value and effect of rapid thermal annealing (RTA). RTA at 700 degrees C was shown to reduce concentrations of the studied defects but it introduced a new defect that likely directly participates in the monitored radiative recombination process in the RTA-treated samples. (c) 2005 Elsevier B.V. All rights reserved.

  • 292.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan.
    Abernathy, C.R.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Pearton, S.J.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Spin depolarization in semiconductor spin detectors2006In: Proc. of SPIE Vol. 6118: Ultrafast Phenomena in Semiconductors and Nanostructure Materials X / [ed] K.-T. Tsen, J.-J. Song, H. Jiang, SPIE - International Society for Optical Engineering, 2006, p. 611804-1-611804-12Conference paper (Other academic)
    Abstract [en]

    A brief review is given of our recent experimental results from in-depth investigations of spin depolarization and underlying physical mechanisms within semiconductor spin detectors based on II-VIs (e.g. Zn(Cd)Se quantum wells) and III-Vs (e.g. InGaN quantum wells), which are relevant to applications for spin-LEDs based on ZnMnSe/Zn(Cd)Se and GaMnN/InGaN structures. By employing cw and time-resolved magneto-optical and optical spin orientation spectroscopy in combination with tunable laser excitation, we show that spin depolarization within these spin detectors is very efficient and is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.

  • 293.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nishibayashi, K.
    Kayanuma, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Thaler, G.
    Frazier, R.
    Abernathy, C.R.
    Ren, F.
    Pearton, S.J.
    Pan, C.C.
    Chen, G.T.
    Chyi, J.I.
    Transient Magneto-optical Spectroscopy of Spin-LED Structures2006In: 11th International Conferences on Modern Materials and Technologies,2006, 2006, p. SS2.1:P0-Conference paper (Other academic)
    Abstract [en]

      

  • 294. Kayanuma, K
    et al.
    Seo, K
    Nishibayashi, K
    Murayama, A
    Oka, Y
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Transient photoluminescence spectroscopy of spin injection dynamics in double quantum wells of diluted magnetic semiconductors2006In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 119, p. 418-422Article in journal (Refereed)
    Abstract [en]

    Dynamics of spin injection has been studied in double quantum wells (DQWs) composed of diluted magnetic and non-magnetic semiconductors. Picosecond-transient photoluminescence (PL) of excitons in the DQWs has been measured in magnetic field. In the Cd1-xMnxTe-based DQWs, the PL intensity of the magnetic well (MW) excitons decays faster with decreasing barrier width from 12 to 2 nm. This provides the evidence for carrier tunneling from the MW to the non-magnetic well (NW) through the barrier layer. The degree of circular polarization in the transient PL of the NW exciton in magnetic field shows marked evidence for spin injection and rapid spin relaxation in the DQW system. In the Zn1-yMnySe-based DQWs, the degree of circle polarization in the NW exciton PL at 3T shows a rise with a time constant of 400 ps, while the PL of the MW exciton decays within 50 ps. The observed result is interpreted by the individual spin injection for electrons and holes from the MW to the NW. The results of the transient PL of excitons in the DQWs are compared with the transient absorptions of excitons studied by the pump-and-probe spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.

  • 295.
    Buyanova, Irina A
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Izadifard, Morteza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Seppänen, Timo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Pearton, SJ
    Polimeni, A
    Capizzi, M
    Brandt, MS
    Bihler, C
    Hong, YG
    Tu, CW
    Unusual effects of hydrogen on electronic and lattice properties of GaNP alloys2006In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, p. 568-570Article in journal (Refereed)
    Abstract [en]

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

  • 296.
    Izadifard, Morteza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Mtchedlidze, T.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Vorona, Igor
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Buyanova, Irina A.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hong, Y.G.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA.
    Tu, C.W.
    Department of Electrical and Computer Engineering, University of California, San Diego, CA.
    Band alignment in GaInNP/GaAs heterostructures grown by gas-source molecular-beam epitaxy2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 26, p. 261904-Article in journal (Refereed)
    Abstract [en]

    Low-temperature photoluminescence (PL), PL excitation, and optically detected cyclotron resonance measurements are employed to determine band alignment in GaInNP/GaAs heterostructures grown by gas-source molecular-beam epitaxy. The type II band alignment at the Ga0.46In0.54NxP1−x/GaAs interface is concluded for the alloys with x ≥ 0.5% based on (i) highly efficient PL upconversion observed in the N containing samples and (ii) appearance of a near-infrared PL emission attributed to the spatially indirect type II transitions. Compositional dependence of the conduction band offset at the Ga1−yInyNxP1−x/GaAs interface is also estimated.

  • 297.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Tu, C.W.
    Yonezu, H.
    Defects in dilute nitrides2005Conference paper (Refereed)
    Abstract [en]

    We provide a brief review of our recent results from optically detected magnetic resonance studies of grown-in non-radiative defects in dilute nitrides, i.e. Ga(In)NAs and Ga(Al,In)NP. Defect complexes involving intrinsic defects such as As-Ga antisites and Ga-i self-interstitials were positively identified. Effects of growth conditions, chemical compositions and post-growth treatments on formation of the defects are closely examined. These grown-in defects are shown to play an important role in non-radiative carrier recombination and thus in degrading optical quality of the alloys, harmful to performance of potential optoelectronic and photonic devices based on these dilute nitrides.

  • 298.
    Buyanova, Irina A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Rudko, G.Yu.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Kayanuma, K.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
    Murayama, A.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
    Toropov, A.A.
    A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Sorokin, S.V.
    A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Ivanov, S.V.
    A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26, St. Petersburg 194021, Russian Federation.
    Effect of momentum relaxation on exciton spin dynamics in diluted magnetic semiconductor ZnMnSe CdSe superlattices2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 16Article in journal (Refereed)
    Abstract [en]

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

  • 299.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Izadifard, Morteza
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Xin, H.P.
    Tu, C.W.
    Pearton, S.J.
    Effects of N incorporation on the electronic structure of GaNP: Origin of the 2.87 eV optical transition2005Conference paper (Refereed)
    Abstract [en]

    Temperature dependent photoluminescence excitation (PLE) spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered (I. A. Buyanova et al, PRB 69, 201303 (2004)) in the GaNxP1-x alloys. Whereas appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with N content. This questions a possible association of this feature with a N-related localized state. Based on the results of temperature dependent measurements, the involved state is concluded to have a non-$\Gamma $ character. Excitation of the known N-related localized states via this state is found to be non-selective, opposed to that between the N-related centers. The observed properties are shown to be hardly consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the ``2.87 eV'' state as being due to either a t2 component of the X3c (or L1c CBM or a level arising from a complex of N and H (in some form) are also discussed.

  • 300.
    Izadifard, Morteza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bergman, Peder
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Utsumi, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, Japan.
    Furukawa, Y.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, Japan.
    Wakahara, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, Japan.
    Yonezu, H.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, Japan.
    Effects of rapid thermal annealing on optical properties of GaNxP1−x alloys grown by solid source molecular beam epitaxy2005In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 20, no 5, p. 353-356Article in journal (Refereed)
    Abstract [en]

    Temperature-dependent photoluminescence (PL), PL excitation and time-resolved PL measurements were employed to study the effects of rapid thermal annealing (RTA) on optical properties of GaNxP1−x alloys grown by solid source molecular beam epitaxy. A substantial increase in radiative efficiency of GaNP epilayers, which is especially pronounced for the high-energy PL component, was achieved after RTA and is attributed to annealing out of competing non-radiative centres. The latter is evident from reduced quenching of the PL intensity with increasing measurement temperature, which results in a strong increase (up to 18 times) in the PL intensity at room temperature (RT), as well as from a substantial increase in carrier lifetime at RT deduced from time-resolved PL measurements.

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