| 1. |
- Huang, Yuqing, et al.
(författare)
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Effect of a Phonon Bottleneck on Exciton and Spin Generation in Self-Assembled In1-xGaxAs Quantum Dots
- 2018
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- We provide direct experimental evidence for the effect of a phonon bottleneck on exciton and spin generation in self-assembled In0.5Ga0.5As quantum dots (QDs). With the aid of tunable laser spectroscopy, we resolve and identify efficient exciton generation channels in the QDs mediated by longitudinal-optical (LO) phonons from an otherwise inhomogeneously broadened QD emission background that suffers from the phonon bottleneck effect in exciton generation. Spin-generation efficiency is found to be enhanced under the LO-assisted excitation condition due to suppressed spin relaxation accompanying accelerated exciton generation. These findings underline the importance of fine-tuning QD energy levels that will benefit potential spin-optoelectronic applications of QDs by reducing spin loss due to the phonon bottleneck.
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| 2. |
- Huang, Yuqing, et al.
(författare)
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Oblique Nuclear Quadrupole Interaction in Self-Assembled Structures Based on Semiconductor Quantum Dots
- 2020
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic nuclear polarization (DNP) is well recognized as being important in spintronics and quantum-information processing. DNP gives rise to high nuclear spin polarization that not only can prolong electron-spin lifetime by generating an Overhauser field (OHF), but also has fertilized the idea to explore nuclear spin qubits. In strained quantum-dot structures (QDSs), a nuclear spin is coupled to a strain field via its quadrupole moment. It has been shown that such nuclear quadrupole interaction (NQI) can be used to achieve appreciable DNP and hence electron-spin polarization. Here, we uncover magneto-optical anomalies from a series of laterally arranged (In,Ga)As QDSs that arise from the NQI and DNP in these nanostructures. We find that the principal axis of NQI in symmetry-lowered QDSs significantly deviates from the growth direction, resulting in tilting of OHF with an angle exceeding 37 degrees. The resulting transverse component of OHF is probed with respect to the crystallographic orientations and its influence on the DNP and ensemble spin dephasing is analyzed. We show that a high-symmetry electronic confinement potential for excitons does not guarantee a high-symmetry NQI for nuclei within the same nano-object, thereby calling for correlated optimization in the symmetry of the electronic confinement potential and that of the nuclear spin bath. Our results underline the role of oblique NQI in electron-spin decoherence and depolarization, which has so far largely been overlooked. This work thus sheds light on design rules for engineering the electronic and spin landscape of QDSs for better performance of DNP desirable for applications in spintronics and quantum computation.
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| 3. |
- Huang, Yuqing, et al.
(författare)
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Tuneable Nonlinear Spin Response in a Nonmagnetic Semiconductor
- 2023
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 19:6
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Tidskriftsartikel (refereegranskat)abstract
- Nonlinear effects and dynamics are found in a wide range of research fields. In magnetic materials, nonlinear spin dynamics enables ultrafast manipulation of spin, which promises high-speed nonvolatile information processing and storage for future spintronic applications. However, a nonlinear spin response is not yet demonstrated in a nonmagnetic material that lacks strong magnetic interactions. Dilute nitride III-V materials, e.g., (Ga, N)As, have the ability to amplify the conduction-electron-spin polarization by filtering out minority spins via spin-polarized defect states at room temperature. Here, by employing coupled rate equations, we theoretically demonstrate the emergence of a nonlinear spin response in such a defect-enabled room-temperature spin amplifier. Furthermore, we showcase the proposed spin nonlinearity in a (Ga, N)As-InAs quantum dot (QD) coupled all-semiconductor nanostructure, by measuring the higher-harmonic generation, which converts the modulation of excitation polarization into the second-, third-, and fourth-order harmonic oscillations of the QDs photoluminescence intensity and polarization. The observed spin nonlinearity originates from defect-mediated spin-dependent recombination, which can be conveniently tuned with an external magnetic field and can potentially operate at a speed exceeding 1 GHz. The demonstrated spin nonlinearity could pave the way for nonlinear spintronic and optospintronic device applications based on nonmagnetic semiconductors with simultaneously achievable high operation speed and nonlinear response.
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| 4. |
- Jansson, Mattias, et al.
(författare)
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N-induced Quantum Dots in GaAs/Ga(N, As) Core/Shell Nanowires: Symmetry, Strain, and Electronic Structure
- 2018
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires (NWs) with embedded zero-dimensional (0D) quantum dots (QDs) have interesting fundamental properties attractive for a variety of applications. The properties of such embedded QDs can be controlled by 0D quantum confinement and also via strain engineering in axial or radial heterostructures of the nanowire system. We evaluate the electronic structure of QDs, which are formed in the Ga(N, As) shell of the GaAs/Ga(N, As) core-shell NWs due to alloy fluctuations. It is found that the principal quantization axis of the studied QDs is primarily oriented along the NW axis, based on the performed polarizationresolved magneto-photoluminescence measurements. We also show that the QDs exhibit a large spectrally dependent variation of the valence band character, which changes from pure heavy-hole states for the low-energy QD emitters to the mixed light-hole heavy-hole states for the QDs emitting at high energies. We ascribe these changes to combined effects of the uniaxial strain caused by the lattice mismatch between the GaAs core and the Ga(N, As) shell, and the local strain/lattice distortion within the short-range fluctuations in the N content. The obtained results underline the importance of the local strain for valence band engineering in hybrid NW structures with embedded QDs.
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| 5. |
- Stehr, Jan Eric, et al.
(författare)
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Efficient Auger Charge-Transfer Processes in ZnO
- 2018
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence and magneto-optical measurements are performed on a line peaking at 3.354 eV (labeled as NBX) in electron-irradiated ZnO. Even though the energy position of the NBX line is close to that for bound excitons in ZnO, it has distinctively different magneto-optical properties. Photoelectron paramagnetic resonance measurements reveal a connection and a charge-transfer process involving NBX and Fe and Al centers. The experimental results are explained within a model which assumes that the NBX is a neutral donor bound exciton at a defect center located near a Fe impurity and an Auger-type charge-transfer process occurs between NBX and Fe3+. While the NBX dissociates, its hole is captured by an excited state of Fe3+ and the released energy is transferred to the NBX electron, which is excited to the conduction band and subsequently trapped by a substitutional Al-zn shallow donor.
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| 6. |
- Stehr, Jan Eric, et al.
(författare)
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Zinc-Vacancy–Donor Complex : A Crucial Compensating Acceptor in ZnO
- 2014
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 2:021001
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Tidskriftsartikel (refereegranskat)abstract
- The aluminum–zinc-vacancy (Al Zn −V Zn ) complex is identified as one of the dominant defects in Al-containing n -type ZnO after electron irradiation at room temperature with energies above 0.8 MeV. The complex is energetically favorable over the isolated V Zn , binding more than 90% of the stable V Zn ’s generated by the irradiation. It acts as a deep acceptor with the (0/− ) energy level located at approximately 1 eV above the valence band. Such a complex is concluded to be a defect of crucial and general importance that limits the n -type doping efficiency by complex formation with donors, thereby literally removing the donors, as well as by charge compensation.
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