| 1. |
- 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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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Pearton, S.J., et al.
(författare)
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ZnO doped with transition metal ions
- 2007
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 54:5, s. 1040-1048
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Anderson, Dan, 1943, et al.
(författare)
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Microwave breakdown in RF devices
- 2006
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Ingår i: 33rd European Physical Society Conference on Plasma Physics, Rome, June 19-23, 2006. ; , s. 429-
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Konferensbidrag (refereegranskat)
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| 8. |
- Buyanova, Irina A, et al.
(författare)
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Effects of Ga doping on optical and structural properties of ZnO epilayers
- 2009
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 45:4-5, s. 413-420
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Tidskriftsartikel (refereegranskat)abstract
- Effects of Ga incorporation on electrical, structural and optical properties of ZnO epilayers are systematically studied by employing structural and optical characterization techniques combined with electrical and secondary ion mass spectrometry measurements. A non-monotonous dependence of free electron concentrations on Ga content is observed and is attributed to defect formation and phase separation. The former process is found to dominate for Ga concentrations of around 2-3x1020 cm-3. corresponding defects are suggested to be responsible for a broad red emission, which peaks at around 1.8 eV at K. Characteristic properties of this emission are well accounted for by assuming intracenter transitions at a deep center, of which the associated Huang-Rhys factor and mean phonon energy are determined. For higher Ga doping levels, the phase separation is found to be significant. It is that under these conditions only a minor fraction of incorporated Ga atoms form shallow donors, which leads to the observed dramatic decrease of carrier concentration.
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| 9. |
- Buyanova, Irina A, et al.
(författare)
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Unusual effects of hydrogen on electronic and lattice properties of GaNP alloys
- 2006
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 376, s. 568-570
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Band alignment in novel GaInNP/GaAs heterostructures.
- 2007
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Ingår i: 31th Workshop on Compound Semiconductor Devices and Integrated Circuits WOCSDICE 2007,2007. ; , s. 183-186
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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