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Träfflista för sökning "hsv:(NATURVETENSKAP) hsv:(Fysik) hsv:(Den kondenserade materiens fysik) ;pers:(Buyanova Irina 1960)"

Sökning: hsv:(NATURVETENSKAP) hsv:(Fysik) hsv:(Den kondenserade materiens fysik) > Buyanova Irina 1960

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1.
  • Bian, Qingzhen, 1988-, et al. (författare)
  • Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes
  • 2020
  • Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 11:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial 200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications.
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3.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Defects in dilute nitrides
  • 2004
  • Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16, s. S3027-S3035
  • Forskningsöversikt (refereegranskat)abstract
    • An overview of our present knowledge and understanding of defects in dilute nitrides will be provided and their important roles in determining the success of dilute nitrides for optoelectronic device applications will be underlined. A brief summary of experimental results of defects by various techniques reported so far in the literature will be given. Our recent results from optically detected magnetic resonance studies of grown-in non-radiative defects in Ga(In)NAs and Ga(Al, In)NP will be discussed in some detail, in an effort to provide chemical identification and experimental signatures of defects. Among them, intrinsic defects such as antisites and self-interstitials have been positively identified, and the effects of growth conditions, chemical compositions and post-growth processing on the formation of the defects were studied. The information retrieved from the experimental findings is expected to provide useful guidance for designing strategies to eliminate defects that are harmful to device performance.
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4.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Effects of N incorporation on the electronic structure of GaNP : Origin of the 2.87 eV optical transition
  • 2005
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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5.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Hydrogen passivation of nitrogen in GaNAs and GaNP alloys : How many H atoms are required for each N atom?
  • 2007
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:2, s. 021920-
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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6.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Transient Spectroscopy of Optical Spin Injection in ZnMnSe/ZnCdSe Quantum Structures
  • 2005
  • Ingår i: Journal of Superconductivity. - Journal of Superconductivity and Novel Magnetism, vol. 18 : Springer. - 0896-1107 .- 1572-9605.
  • Konferensbidrag (refereegranskat)abstract
    • We show, by time-resolved magneto-photoluminescence (PL) spectroscopy in combination with selective laser excitation, that optical polarization of the ZnCdSe spin detector induced by spin injection from the ZnMnSe spin injector persists over a much longer time scale than the lifetime of the ZnMnSe excitons. This finding provides compelling experimental evidence that the dominant mechanism for the observed spin injection in the ZnMnSe/ZnCdSe structures should not be due to injection of the excitonic spins of the diluted magnetic semiconductor (DMS). It is rather due to e.g. a delayed spin injection arising from tunneling of individual carriers or/and trapped spins in ZnMnSe.
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7.
  • Chen, Weimin, 1959-, et al. (författare)
  • Defects in dilute nitrides
  • 2005
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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8.
  • Chen, Weimin, 1959-, et al. (författare)
  • Defects in dilute nitrides : significance and experimental signatures
  • 2004
  • Ingår i: IEE Proceedings - Optoelectronics. - Optoelectronics, IEE Proceedings, Vol. 151, Issue 5 : IET. - 1350-2433 .- 1359-7078.
  • Konferensbidrag (refereegranskat)abstract
    • A brief review of experimental results of defects in dilute nitrides studied by various techniques reported so far in the literature is given. The emphasis is on experimental signatures of grown-in defects in Ga(In)NAs and Ga(Al)NP, which are expected to play important roles in device performance and in determining the success of this novel material system for applications in optoelectronics. The authors' recent results from optically detected magnetic resonance studies of grown-in intrinsic defects, i.e. AsGa antisite in Ga(In)NAs and Ga self-interstitials in Ga(Al,In)NP, are discussed in more detail, in an effort to provide detailed information on the chemical identification and the formation mechanism of the defects as well as to reveal their role in degrading the optical quality of the materials. The review aims not only to provide an overview of the present knowledge and understanding of defects in dilute nitrides, but also to stress the urgent need for concerted efforts to positively identify the most important defects that are harmful to device performance and to design strategies to suppress them during growth or to eliminate them by post-growth treatments.
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10.
  • Chen, Weimin, 1959-, et al. (författare)
  • Spin depolarization in semiconductor spin detectors
  • 2006
  • Ingår i: Proc. of SPIE Vol. 6118. - : SPIE - International Society for Optical Engineering. ; , s. 611804-1-611804-12
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
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