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- Chen, Weimin, et al.
(författare)
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How to Deactivate Harmful Defects and Active them for New Spin Functionalities in a Semiconductor?
- 2015
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Ingår i: Abstract Book. ; , s. FF3.02-
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Konferensbidrag (refereegranskat)abstract
- We demonstrate a general approach via spin engineering that is capable of not only deactivating defect-mediated efficient non-radiative carrier recombination channels in a semiconductor that are harmful to photonic and photovoltaic device performance, but also adding new room-temperature (RT) spin functionalities that are desirable for future spintronics and spin-photonics but so far unachievable otherwise. This approach exploits the Pauli Exclusion Principle that prohibits occupation of a non-degenerate defect level by two spin-parallel electrons, thereby providing spin blockade of carrier recombination via the defect level. The success of the approach is demonstrated in the dilute nitride of Ga(In)NAs, which holds promises for low-cost, highly efficient lasers for fiber-optic communications as well as for multi-band and multi-junction solar cell applications. First we identify that Gai self-interstitials and their complexes are the most common grown-in defects found in Ga(In)NAs grown by both molecular beam epitaxy (MBE) and metalorganic chemical vapour deposition (MOCVD). They provide a dominant non-radiative shunt path for non-equilibrium carriers, leading to low efficiencies of light-emitting and photon-charge carrier conversion. Spin blockade is shown to lead to a giant enhancement by up to 800% in light emission intensity at RT.Furthermore we show that via spin engineering these seemingly harmful defects can be turned into advantages by adding unconventional defect-enabled spin functionalities that are highly effective at RT, including some of the fundamental building blocks essential for future spintronics. We demonstrate efficient defect-engineered spin filtering in Ga(In)NAs, which is capable of generating a record-high degree (> 40%) of electron spin polarization at RT [Nature Materials 8, 198 (2009), Phys. Rev. B 89, 195412 (2014)]. We also provide the first experimental demonstration of an efficient RT spin amplifier based on defect engineered Ga(In)NAs with a spin gain up to 2700% [Adv. Materials 25, 738 (2013)]. Such a spin amplifier is shown to be capable of amplifying a fast-modulating input spin signal while truthfully maintaining its time variation of the spin-encoded information [7]. By taking advantage of the spin amplification effect, we show that Ga(In)NAs can be employed as efficient RT spin detectors, with spin detection efficiency well exceeding 100% [8,9]. By combining the spin-filtering effect and hyperfine coupling, we further achieve the first realization of RT nuclear spin hyperpolarization in semiconductors via conduction electrons [Nature Communications. 4, 1751 (2013)], relevant to nuclear spin qubits. We believe that such defect-enabled spin functionalities could potentially provide an attractive, alternative solution to the current and important issues on RT spin injection, spin amplification and spin detection in semiconductors for future spintronics.
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- Dagnelund, Daniel, 1980-, et al.
(författare)
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Optically detected cyclotron resonance studies of InGaNAs/GaAs structures
- 2007
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Ingår i: Physics of semiconductors : 28th International Conference on the Physics of Semiconductors, ICPS 2006, Vienna, Austria, 24-28 July 2006. - : American Institute of Physics (AIP). - 9780735403970 ; , s. 383-384
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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 m∗e. 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
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- Dagnelund, Daniel, 1980-, et al.
(författare)
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Optically detected cyclotron resonance studies of InxGa1-xNyAs1-y/GaAs quantum wells sandwiched between type-II AlAs/GaAs superlattices.
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101, s. 073705-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Puttisong, Yuttapoom, et al.
(författare)
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Efficient room-temperature nuclear spin hyperpolarization of a defect atom in a semiconductor
- 2013
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 4:1751
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we demonstrate that a combined effect of efficient spin-dependent recombination and hyperfine coupling can facilitate strong dynamic nuclear polarization of a defect atom in a semiconductor at room temperature. We provide direct evidence that a sizeable nuclear field (~150 Gauss) and nuclear spin polarization (~15%) sensed by conduction electrons in GaNAs originates from dynamic nuclear polarization of a Ga interstitial defect. We further show that the dynamic nuclear polarization process is remarkably fast and is completed in <5 μs at room temperature. The proposed new concept could pave a way to overcome a major obstacle in achieving strong dynamic nuclear polarization at room temperature, desirable for practical device applications.
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- Puttisong, Yuttapoom, et al.
(författare)
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Efficient room-temperature spin detector based on GaNAs
- 2012
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 111:7, s. 07C303-
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Tidskriftsartikel (refereegranskat)abstract
- Efficient and highly spin-dependent recombination processes are shown to not only turn GaNAs into an efficient spin filter but also to make it an excellent spin detector functional at room temperature (RT). By taking advantage of the defect-engineered spin-filtering effect, the spin detection efficiency is no longer limited by the fast spin relaxation of conduction electrons. This leads to a significant enhancement in the optical polarization of the spin detector, making it possible to reliably detect even very weak electron spin polarization at RT, as demonstrated by a study of spin loss during optical spin injection across a GaAs/GaNAs interface.
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| 8. |
- Puttisong, Yuttapoom, et al.
(författare)
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Room-temperature spin injection and spin loss across a GaNAs/GaAs interface
- 2011
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Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 98:1, s. 012112-
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Tidskriftsartikel (refereegranskat)abstract
- Recently discovered effect of spin-filtering and spin amplification in GaNAs enables us to reliably obtain detailed information on the degree of spin loss during optical spin injection across a semiconductor heterointerface at room temperature. Spin polarization of electrons injected from GaAs into GaNAs is found to be less than half of what is generated in GaNAs by optical orientation. We show that the observed reduced spin injection efficiency is not only due to spin relaxation in GaAs, but more importantly due to spin loss across the interface due to structural inversion asymmetry and probably also interfacial point defects.
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| 10. |
- Wang, Xingjun, et al.
(författare)
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Dominant recombination centers in Ga(In)NAs alloys: Ga interstitials
- 2009
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Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 95, s. 241904-
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Tidskriftsartikel (refereegranskat)abstract
- Opticallydetected magnetic resonance measurements are carried out to study formationof Ga interstitial-related defects in Ga(In)NAs alloys. The defects, whichare among dominant nonradiative recombination centers that control carrier lifetimein Ga(In)NAs, are unambiguously proven to be common grown-in defectsin these alloys independent of the employed growth methods. Thedefects formation is suggested to become thermodynamically favorable because ofthe presence of nitrogen, possibly due to local strain compensation.
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