| 1. |
- Polimeni, A., et al.
(författare)
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Hydrogen related effects in diluted nitrides
- 2003
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Ingår i: 22nd Int. Conf. on Defects in Semiconductors,2003. - : Elsevier. ; , s. 371-
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Konferensbidrag (refereegranskat)abstract
- Hydrogen irradiation leads to the passivation of the electronic activity of nitrogen in Ga(AsN), thus allowing a fine tuning of the material optical properties. Here, some recent results on the effects that hydrogen irradiation has on the electronic properties of diluted III-N-V alloys are presented. In Ga(AsN), both the increase in the electron effective mass and exciton wave function localization induced by nitrogen are reversed in a fully controllable manner by hydrogen irradiation. In Ga(PN), hydrogen widens the band gap and exposes gradually in the gap nitrogen complex states formerly resonant with the conduction band.
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| 2. |
- Polimeni, A., et al.
(författare)
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Nitrogen passivation induced by atomic hydrogen : The GaP1-yNy case
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:20, s. 2013031-2013034
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Tidskriftsartikel (refereegranskat)abstract
- We report on the evolution of the optical properties of GaP1-yNy epilayers upon hydrogen irradiation for an extended nitrogen concentration range (y = 0.05% - 1.3%). For y = 0.6%, photoluminescence measurements show that hydrogen leads to an apparent band gap widening and to an ensuing appearance of N cluster states in the forbidden gap of GaP1-yNy, Hydrogen removal from the samples results in a full recovery of the electronic properties of the as-grown material. For lower N concentration (y = 0.05%), hydrogen causes a spectral weight transfer from electronic levels associated with closer N pairs to those associated with more distant N pairs and single N atoms.
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| 3. |
- Buyanova, Irina A., et al.
(författare)
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Strain relaxation in GaNxP1-x alloy : Effect on optical properties
- 2001
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 308-310, s. 106-109
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Tidskriftsartikel (refereegranskat)abstract
- By using scanning electron microscopy and cathodoluminescence (CL), a decrease in radiative efficiency of GaNP alloy with increasing N content is seen due to the formation of structural defects. The defect formation is attributed to relaxation of tensile strain in the GaNP layer, which is lattice mismatched to GaP substrate. Several types of extended defects including dislocations, microcracks and pits are revealed in partly relaxed GaNxP1-x epilayers with x=1.9%, whereas coherently strained layers exhibit high crystalline quality for x up to 4%. According to the CL measurements, all extended defects act as competing, non-radiative channels leading to the observed strong decrease in the radiative efficiency. From CL mapping experiments, non-uniformity of strain distribution around the extended defects is partly responsible for the broadening of the photoluminescence (PL) spectra recorded in the macro-PL experiments. © 2001 Elsevier Science B.V. All rights reserved.
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| 4. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Direct experimental evidence for unusual effects of hydrogen on the electronic and vibrational properties of GaNxP1−x alloys : a proof for a general property of dilute nitrides
- 2004
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 70:24, s. 245215-245219
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Tidskriftsartikel (refereegranskat)abstract
- Direct experimental evidence for dramatic effects of hydrogen incorporation on the electronic structure and lattice properties of GaNxP1−x alloys is presented. By employing photoluminescence excitation spectroscopy, postgrowth hydrogenation is shown to reopen the band gap of the GaNP alloys and to efficiently reduce the N-induced coupling between the conduction band states. By Raman spectroscopy, these effects are shown to be accompanied by hydrogen-induced breaking of the Ga-P bond in the alloy, evident from disappearance of the corresponding vibrational mode. According to the performed Raman and x-ray diffraction measurements, the hydrogenation is also found to cause a strong expansion of the GaNP lattice, which changes the sign of strain from tensile in the as-grown GaNP epilayers to compressive in the posthydrogenated structures, due to the formation of complexes between N and H.
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| 5. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Optical characterization of ZnMnO-based dilute magnetic semiconductor structures
- 2006
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 24:1, s. 259-262
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
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| 7. |
- Felici, M, et al.
(författare)
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High Energy Optical Transitions in Ga(PN) : Contribution from Perturbed Valence Band
- 2005
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Ingår i: AIP Conference Proceedings / Volume 772. - : American Institute of Physics (AIP). - 0735402574 ; , s. 265-
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Konferensbidrag (refereegranskat)abstract
- The GaP1–xNx conduction band is investigated experimentally (by excitation photoluminescence) andtheoretically (by pseudopotential supercells) for N concentrations up to x=3.5%and photon energies ranging from the optical absorption edge to3.2 eV. With increasing x: (i) a direct-like absorption edgedevelops smoothly and red-shifts rapidly overtaking energy-pinned cluster states; (ii)a broad absorption plateau appears between the X1c and the1c critical points of GaP; (iii) the 1c absorption edgebroadens and gradually disappears. Empirical pseudopotential calculations for GaP1-xNx randomalloy supercells account well for all the PLE results byconsidering N induced changes in the valence band overlooked sofar. ©2005 American Institute of Physics
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| 8. |
- Göransson, D. J.O., et al.
(författare)
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Measurements of Strain and Bandgap of Coherently Epitaxially Grown Wurtzite InAsP-InP Core-Shell Nanowires
- 2019
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:4, s. 2674-2681
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Tidskriftsartikel (refereegranskat)abstract
- 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 (μPL) spectroscopy, and micro-Raman (μ-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 μPL 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.
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| 9. |
- Pearton, S. J., et al.
(författare)
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Ferromagnetism in transition-metal doped ZnO
- 2007
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 36:4, s. 462-471
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Forskningsöversikt (refereegranskat)abstract
- 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.
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| 10. |
- Pearton, Stephen J., et al.
(författare)
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Transition Metal Doped ZnO for Spintronics
- 2007
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Ingår i: MRS Proceedings 2007 vol. 999. - Warrendale, PA : Materials Research Society. ; , s. 0999-K03-K04
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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