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  • 1.
    Chen, Shula
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Visser, Dennis
    KTH Royal Inst Technol, Sweden.
    Anand, Srinivasan
    KTH Royal Inst Technol, Sweden.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Room-temperature polarized spin-photon interface based on a semiconductor nanodisk-in-nanopillar structure driven by few defects2018Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 9, artikel-id 3575Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Owing to their superior optical properties, semiconductor nanopillars/nanowires in one-dimensional (1D) geometry are building blocks for nano-photonics. They also hold potential for efficient polarized spin-light conversion in future spin nano-photonics. Unfortunately, spin generation in 1D systems so far remains inefficient at room temperature. Here we propose an approach that can significantly enhance the radiative efficiency of the electrons with the desired spin while suppressing that with the unwanted spin, which simultaneously ensures strong spin and light polarization. We demonstrate high optical polarization of 20%, inferring high electron spin polarization up to 60% at room temperature in a 1D system based on a GaNAs nanodisk-in-GaAs nanopillar structure, facilitated by spin-dependent recombination via merely 2-3 defects in each nanodisk. Our approach points to a promising direction for realization of an interface for efficient spin-photon quantum information transfer at room temperature-a key element for future spin-photonic applications.

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  • 2.
    Chen, Shula
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Jansson, Mattias
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Stehr, Jan Eric
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Ishikawa, Fumitaro
    Ehime University, Japan.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Dilute Nitride Nanowire Lasers Based on a GaAs/GaNAs Core/Shell Structure2017Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, nr 3, s. 1775-1781Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanowire (NW) lasers operating in the near infrared spectral range are of significant technological importance for applications in telecommunications, sensing, and medical diagnostics. So far, lasing within this spectral range has been achieved using GaAs/AlGaAs, GaAs/GaAsP, and InGaAs/GaAs core/shell NWs. Another promising III-V material, not yet explored in its lasing capacity, is the dilute nitride GaNAs. In this work, we demonstrate, for the first time, optically pumped lasing from the GaNAs shell of a single GaAs/GaNAs core/shell NW. The characteristic "S"-shaped pump power dependence of the lasing intensity, with the concomitant line width narrowing, is observed, which yields a threshold gain, g(th), of 3300 cm(-1) and a spontaneous emission coupling factor beta, of 0.045. The dominant lasing peak is identified to arise from the HE21b, cavity mode, as determined from its pronounced emission polarization along the NW axis combined with theoretical calculations of lasing threshold for guided modes inside the nanowire. Even without intentional pas sivation of the NW surface, the lasing emission can be sustained up to 150 K. This is facilitated by the improved surface quality due to nitrogen incorporation, which partly suppresses the surface-related nonradiative recombination centers via nitridation. Our work therefore represents the first step toward development of room-temperature infrared NW lasers based on dilute nitrides with extended tunability in the lasing wavelength.

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  • 3.
    Chen, Yang
    et al.
    Natl Univ Singapore, Singapore; Univ Sci & Technol China, Peoples R China.
    Feng, Jiangang
    Nanyang Technol Univ, Singapore; Natl Univ Singapore, Singapore.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten. Nanyang Technol Univ, Singapore.
    Chen, Weijin
    Natl Univ Singapore, Singapore.
    Su, Rui
    Nanyang Technol Univ, Singapore.
    Ghosh, Sanjib
    Beijing Acad Quantum Informat Sci, Peoples R China.
    Hou, Yi
    Natl Univ Singapore, Singapore; Natl Univ Singapore, Singapore.
    Xiong, Qihua
    Beijing Acad Quantum Informat Sci, Peoples R China; Tsinghua Univ, Peoples R China; Frontier Sci Ctr Quantum Informat, Peoples R China.
    Qiu, Cheng-Wei
    Natl Univ Singapore, Singapore.
    Compact spin-valley-locked perovskite emission2023Ingår i: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Circularly polarized light sources with free-space directional emission play a key role in chiroptics(1), spintronics(2), valleytronics(3) and asymmetric photocatalysis(4). However, conventional approaches fail to simultaneously realize pure circular polarization, high directionality and large emission angles in a compact emitter. Metal-halide perovskite semiconductors are promising light emitters(5-8), but the absence of an intrinsic spin-locking mechanism results in poor emission chirality. Further, device integration has undermined the efficiency and directionality of perovskite chiral emitters. Here we realize compact spin-valley-locked perovskite emitting metasurfaces where spin-dependent geometric phases are imparted into bound states in the continuum via Brillouin zone folding, and thus, photons with different spins are selectively addressed to opposite valleys. Employing this approach, chiral purity of 0.91 and emission angle of 41.0 degrees are simultaneously achieved, with a beam divergence angle of 1.6 degrees. With this approach, we envisage the realization of chiral light- emitting diodes, as well as the on-chip generation of entangled photon pairs.

  • 4.
    Chen, Yang
    et al.
    Chinese Academy of Sciences Key Laboratory of Mechanical Behavior and Design of Materials, Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, People’s Republic of China ; Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore.
    Feng, Jiangang
    Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore ; Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
    Chen, Weijin
    Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore.
    Su, Rui
    Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
    Ghosh, Sanjib
    Beijing Academy of Quantum Information Sciences, Beijing, People’s Republic of China.
    Hou, Yi
    Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, Singapore ; Solar Energy Research Institute of Singapore (SERIS), National University of Singapore, Singapore, Singapore.
    Xiong, Qihua
    Beijing Academy of Quantum Information Sciences, Beijing, People’s Republic of China ; State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, People’s Republic of China ; Frontier Science Center for Quantum Information, Beijing, People’s Republic of China.
    Qiu, Cheng-Wei
    Compact spin-valley-locked perovskite emission2023Ingår i: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 22, nr 9, s. 1065-1070Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Circularly polarized light sources with free-space directional emission play a key role in chiroptics1, spintronics2, valleytronics3 and asymmetric photocatalysis4. However, conventional approaches fail to simultaneously realize pure circular polarization, high directionality and large emission angles in a compact emitter. Metal-halide perovskite semiconductors are promising light emitters5,6,7,8, but the absence of an intrinsic spin-locking mechanism results in poor emission chirality. Further, device integration has undermined the efficiency and directionality of perovskite chiral emitters. Here we realize compact spin-valley-locked perovskite emitting metasurfaces where spin-dependent geometric phases are imparted into bound states in the continuum via Brillouin zone folding, and thus, photons with different spins are selectively addressed to opposite valleys. Employing this approach, chiral purity of 0.91 and emission angle of 41.0° are simultaneously achieved, with a beam divergence angle of 1.6°. With this approach, we envisage the realization of chiral light-emitting diodes, as well as the on-chip generation of entangled photon pairs.

  • 5.
    Dagnelund, Daniel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Yonezu, H.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Japan .
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Dual-wavelength excited photoluminescence spectroscopy of deep-level hole traps in Ga(In)NP2015Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, s. 015701-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By employing photoluminescence(PL) spectroscopy under dual-wavelength optical excitation, we uncover the presence of deep-level hole traps in Ga(In)NP alloys grown by molecular beam epitaxy(MBE). The energy level positions of the traps are determined to be at 0.56 eV and 0.78 eV above the top of the valance band. We show that photo-excitation of the holes from the traps, by a secondary light source with a photonenergy below the bandgapenergy, can lead to a strong enhancement (up to 25%) of the PL emissions from the alloys under a primary optical excitation above the bandgapenergy. We further demonstrate that the same hole traps can be found in various MBE-grown Ga(In)NP alloys, regardless of their growth temperatures, chemical compositions, and strain. The extent of the PL enhancement induced by the hole de-trapping is shown to vary between different alloys, however, likely reflecting their different trap concentrations. The absence of theses traps in the GaNP alloy grown by vapor phase epitaxy suggests that their incorporation could be associated with a contaminant accompanied by the N plasma source employed in the MBEgrowth, possibly a Cu impurity.

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  • 6.
    Filippov, Stanislav
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Suraprapapich, Suwaree
    Department of Electrical and Computer Engineering, University of California, La Jolla, California, United States.
    Tu, Charles. W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California 92093, United States.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Exciton Fine-Structure Splitting in Self-Assembled Lateral InAs/GaAs Quantum-Dot Molecular Structures2015Ingår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, nr 6, s. 5741-5749Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fine-structure splitting (FSS) of excitons in semiconductor nanostructures is a key parameter that has significant implications in photon entanglement and polarization conversion between electron spins and photons, relevant to quantum information technology and spintronics. Here, we investigate exciton FSS in self-organized lateral InAs/GaAs quantum-dot molecular structures (QMSs) including laterally aligned double quantum dots (DQDs), quantum-dot clusters (QCs), and quantum rings (QRs), by employing polarization-resolved microphotoluminescence (μPL) spectroscopy. We find a clear trend in FSS between the studied QMSs depending on their geometric arrangements, from a large FSS in the DQDs to a smaller FSS in the QCs and QRs. This trend is accompanied by a corresponding difference in the optical polarization directions of the excitons between these QMSs, namely, the bright-exciton lines are linearly polarized preferably along or perpendicular to the [11̅0] crystallographic axis in the DQDs that also defines the alignment direction of the two constituting QDs, whereas in the QCs and QRs, the polarization directions are randomly oriented. We attribute the observed trend in the FSS to a significant reduction of the asymmetry in the lateral confinement potential of the excitons in the QRs and QCs as compared with the DQDs, as a result of a compensation between the effects of lateral shape anisotropy and piezoelectric field. Our work demonstrates that FSS strongly depends on the geometric arrangements of the QMSs, which effectively tune the degree of the compensation effects and are capable of reducing FSS even in a strained QD system to a limit similar to strain-free QDs. This approach provides a pathway in obtaining high-symmetry quantum emitters desirable for realizing photon entanglement and spintronic devices based on such nanostructures, utilizing an uninterrupted epitaxial growth procedure without special requirements for lattice-matched materials combinations, specific substrate orientations, and nanolithography.

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  • 7.
    Fillipov, Stanislav
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Suraprapapich, Suwaree
    Department of Electrical and Computer Engineering, University of California, La Jolla, California, USA.
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California, USA.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Control of exciton fine-structure splitting in geometrically engineered self-assembled InAs/GaAs quantum molecular structuresManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Fine-structure splitting (FSS) of excitons in semiconductor nanostructures is a key parameter that has significant implications in photon entanglement and polarization conversion between electron spins and photons, relevant to quantum information technology and spintronics. Here, we investigate exciton FSS in self-organized InAs/GaAs quantum molecular structures (QMSs) including laterally-aligned double quantum dots (DQDs), quantum-dot clusters (QCs) and quantum rings (QRs), by employing polarization-resolved micro-photoluminescence spectroscopy. We find a clear trend in FSS between the studied QMSs depending on their geometric arrangements, from a large FSS in the DQDs to a smaller FSS in the QCs and QRs with an overall higher geometric symmetry. This trend is accompanied by a corresponding difference in the optical polarization directions of the excitons between these QMSs, namely, the bright-exciton lines are linearly polarized preferably along or perpendicular to the [11̅0] crystallographic axis in the DQDs that also defines the alignment of the two constituting QDs, whereas in the QCs and QRs the polarization directions are randomly oriented. We attribute the observed trends in the FSS to a significant reduction of the anisotropic strain field in the high symmetry QCRs and QCs as compared with the low-symmetry  DQDs. Our work demonstrates that FSS can be effectively controlled by geometric engineering of the QMSs, capable of reducing FSS even in a strained QD system to a limit similar to strain-free QDs. This approach provides a new pathway in obtaining high-symmetry quantum emitters desirable for realizing photon entanglement and spintronic devices based on such nanostructures, without special requirements for lattice-matched materials combinations, specific substrate orientations and nanolithography.

  • 8.
    Goransson, D. J. O.
    et al.
    Lund Univ, Sweden.
    Borgstrom, M. T.
    Lund Univ, Sweden.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Messing, M. E.
    Lund Univ, Sweden.
    Hessman, D.
    Lund Univ, Sweden.
    Buyanova, Irina A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Xu, H. Q.
    Lund Univ, Sweden; Peking Univ, Peoples R China; Peking Univ, Peoples R China; Beijing Acad Quantum Informat Sci, Peoples R China.
    Measurements of Strain and Bandgap of Coherently Epitaxially Grown Wurtzite InAsP-InP Core-Shell Nanowires2019Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, nr 4, s. 2674-2681Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 (mu PL) spectroscopy, and micro-Raman (mu-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 mu PL 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.

  • 9.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Spin generation and detection in low-dimensional semiconductors2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Semiconductor spintronics and opto-spintronics have intrigued intense attention as they promise great advance of contemporary semiconductor information technology with integrated spin functionalities. Over the last few decades, the development of growth techniques and discovery of topological band structures have led to the explosion of a wide range of low-dimensional semiconductor materials, many of which have superior properties compared to their bulk ancestors. The limited dimension of materials imposes constraint on the motion of charge carriers and causes spin interactions of various forms, which have profound influence on the spin properties that are important for various spintronic and/or opto-spintronic applications.

    In this context, semiconductor quantum dot (QD) structures (QDS) and 3D topological insulator (TI) have emerged as promising material systems that exhibit distinct spin properties: In QDS, carriers are restricted in all three dimensions. The 3D confinement quenches the spin-orbit interaction (SOI) mediated spin depolarization/dephasing processes and, as a consequence, leads to a prolonged spin relaxation time, which can be used for non-volatile storage or quantum bits in quantum information technology; Whereas, the surface state of 3D TI, on the contrary, has the electronic structure that is dominated by SOI such that the orientation of the electron spin is tied to its momentum. The strong SOI limits the spin relaxation time but can be utilized to generate spin polarized current that is free from backscattering. This thesis work focuses on these two prototypical materials to provide an in-depth understanding of the spin phenomena as well as to tailor their spin properties such that novel spintronic and/or opto-spintronic devices can be built on.

    To employ QDS for storage of spin information, first and foremost is to be able to generate and detect spin polarization effectively and efficiently. For this purpose, we have carefully inspected both the spin injection and spin detection processes in various QDS. In this thesis work, spin polarized carriers or excitons are generated via optical orientation that converts the angular momentum of the absorbed photons to the photo-generated carriers or excitons. The as-generated spin polarized carriers/excitons then need to relax their energy before getting injected to the QDS. We have found that the spin injection process is influenced by the interactions with phonons (Paper 1) and disordered environment associated with the injection path (Paper 2). In the former case, we show that the longitudinal optical (LO) phonon contributes to accelerated relaxation of the carrier/exciton energy to the QDS ground state, which preserves the spin polarization. By engineering the energy of the QDS, we can take advantage of such LO-phonon assisted process and can avoid the spin injection loss due to the commonly observed phonon bottleneck effect. In the latter case, we discover that the surrounding media of the QDS is generally disordered, distributed by potential fluctuations caused by alloying or strain randomness. Exciton injection via such localized potential undergoes spin relaxation caused by an anisotropic exchange interaction (AEI), which leads to appreciable spin injection loss at low temperatures.

    The AEI is also found to be responsible for the low spin detection efficiency observed in the undoped QDS reported in Paper 3. The AEI causes mixing and splitting of exciton spin states, which leads to not only a low PL polarization degree of the QDS but also a serious issue in generation of entangled photon pairs utilizing QDS. We show that the aforementioned spin injection (Paper 2) and spin detection (Paper 3) loss associated with the AEI can be effectively tuned in the QDS by the arrangement of the constituting QDs. The effect originates from the modification of the strain and shape anisotropy both inside and outside the QDS due to the collective interaction with the neighboring QDs, which introduces a new degree of freedom in electronic-structure engineering of the QDS.

    In the doped QDS, we have found that the spin detection efficiency can additionally be affected by the exciton charge states and a hyperfine interaction (HFI) with the nuclear-spin bath. In Paper 4, we discover a dynamic charging process that the charged states of an InGaAs QD ensemble are altered with different excitation power densities and excitation photon energies. The charging effect leads to an anomalous spectral dependence of PL polarization such that the copolarized emission can be dynamically converted to the counter-polarized one. This finding thus calls for caution in the correlation between the optical and spin polarization in QDS with a complex charging environment. The effect of the HFI depends on the condition of nuclear spin polarization. In QDS with an unpolarized nuclear-spin bath, the HFI is a primary electron/exciton spin depolarization/dephasing source in QDS at low temperatures. In Paper 5, we show that the ensemble spin dephasing time of QDs at a cryogenic temperature correlates with the averaged size of QDs. The behavior can be accounted for by electron spin dephasing in a fluctuating nuclear field, which is experimentally verified for the first time. The results thus highlight the important role of the HFI in the electron spin dephasing in the QDs. On the other hand, finite nuclear spin polarization can be achieved through the dynamic nuclear polarization (DNP) process that transfers the angular momentum from the spin-polarized electron to nuclei. DNP is recognized to be important for spintronics and quantum information in nuclear spin-rich nanostructures. This is not only because of its role in suppressing the aforementioned electron spin dephasing, but also because it is behind the idea of exploring the long coherent nuclear spin as a quantum computing qubit. In Paper 6, we have investigated the effect of DNP in a series of QDS, where the strength and orientation of the nuclear field resulted from the DNP are identified and measured. We find that the DNP is built along a tilted axis that deviates from the commonly observed orientation along the QD growth axis and the nuclear field develops a substantial transverse component. This anomalous behavior of the DNP is found to arise from the nuclear quadrupole interaction with an oblique principal axis. The resulting tilting nuclear field can further lead to dephasing and depolarization of the electron spin that has previously been overlooked. The results uncover the detrimental effect rooted in the complex electrostatic environment of the nuclei inside the QDS and call for special care of the strain and alloying engineering of the nanostructures.

    In the case of 3D TI, we aim at providing both the experimental and theoretical understanding of the surface spin photocurrent as well as innovations in future opto-spintronic applications utilizing the semiconductor-TI interface. As has been shown earlier, the circular polarized excitation light creates a spin photocurrent that is resistant to moderate scattering. In Paper 7, we present detailed studies of the dependence of the spin photocurrent on the incident angle of the excitation light in a prototypical 3D TI, Bi2Te3. We point out that the spin photocurrent, as a result of spin-selective optical transitions, is associated with both the in-plane and out-of-plane spin texture of the topological surface states. We focus on the contribution of the out-of-plane spin texture, which is less explored, and demonstrate, for the first time, spin injection from a conventional semiconductor, GaAs, to a 3D TI. In favor of this hybrid system, we show that the spin photocurrent contributed by the spin injection exceeds that from the TI alone and the magnitude and direction of the current can be controlled by applying a transverse magnetic field. In Paper 8, we give a tight-binding description of the microscopic origin of the spin photocurrent in Bi2Te3, where we have provided theoretical calculations of the spin photocurrent as a function of the excitation incidence angle, Fermi energy and different scattering potentials. The results explain the observation of the out-of-plane spin texture contribution reported in Paper 7, which should have been forbidden by symmetry, and provide a pathway for opto-spintronic applications based on a TI-semiconductor hybrid system.

    Delarbeten
    1. Effect of a Phonon Bottleneck on Exciton and Spin Generation in Self-Assembled In1-xGaxAs Quantum Dots
    Öppna denna publikation i ny flik eller fönster >>Effect of a Phonon Bottleneck on Exciton and Spin Generation in Self-Assembled In1-xGaxAs Quantum Dots
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    2018 (Engelska)Ingår i: Physical Review Applied, ISSN 2331-7019, Vol. 9, nr 4, artikel-id 044037Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    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.

    Ort, förlag, år, upplaga, sidor
    AMER PHYSICAL SOC, 2018
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-147924 (URN)10.1103/PhysRevApplied.9.044037 (DOI)000430911800002 ()
    Anmärkning

    Funding Agencies|Linkoping University; Swedish Research Council [621-2011-4254, 2016-05091]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [JA2014-5698]; Japan Society for the Promotion of Science [16H06359]; Bilateral Joint Research Project

    Tillgänglig från: 2018-05-23 Skapad: 2018-05-23 Senast uppdaterad: 2018-09-05
    2. Understanding and optimizing spin injection in self-assembled InAs/GaAs quantum-dot molecular structures
    Öppna denna publikation i ny flik eller fönster >>Understanding and optimizing spin injection in self-assembled InAs/GaAs quantum-dot molecular structures
    2016 (Engelska)Ingår i: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 9, nr 3, s. 602-611Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Semiconductor quantum-dot (QD) structures are promising for spintronic applications owing to strong quenching of spin relaxation processes promoted by carrier and excitons motions. Unfortunately, spin injection efficiency in such nanostructures remains very low and the exact physical mechanism for the spin loss is still not fully understood. Here, we show that exciton spin injection in self-assembled InAs/GaAs QDs and quantum-dot molecular structures (QMSs) is dominated by localized excitons confined within the QD-like regions of the wetting layer (WL) and GaAs barrier layer immediately surrounding QDs and QMSs that in fact lack the commonly believed 2D and 3D character with an extended wavefunction. We identify the microscopic origin of the observed severe spin loss during spin injection as being due to a sizable anisotropic exchange interaction (AEI) of the localized excitons in the WL and GaAs barrier layer, which has so far been overlooked. We find that the AEI of the injected excitons and thus the efficiency of the spin injection processes are correlated with the overall geometric symmetry of the QMSs, as the latter largely defines the anisotropy of the confinement potential of the localized excitons in the surrounding WL and GaAs barrier. These results pave the way for a better understanding of spin injection processes and the microscopic origin of spin loss in QD structures, which in turn provides a useful guideline to significantly improve spin injection efficiency by optimizing the lateral arrangement of the QMSs thereby overcoming a major bottleneck in spintronic device applications utilizing semiconductor QDs.

    Ort, förlag, år, upplaga, sidor
    Tsinghua University Press, 2016
    Nyckelord
    Spin injection, spin loss, quantum dot, quantum - dot molecular structure, InAs/GaAs, exciton, anisotropic exchange interaction, polarization
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-123983 (URN)10.1007/s12274-015-0940-6 (DOI)000371797000002 ()
    Tillgänglig från: 2016-01-15 Skapad: 2016-01-15 Senast uppdaterad: 2018-09-05Bibliografiskt granskad
    3. Exciton Fine-Structure Splitting in Self-Assembled Lateral InAs/GaAs Quantum-Dot Molecular Structures
    Öppna denna publikation i ny flik eller fönster >>Exciton Fine-Structure Splitting in Self-Assembled Lateral InAs/GaAs Quantum-Dot Molecular Structures
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    2015 (Engelska)Ingår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, nr 6, s. 5741-5749Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Fine-structure splitting (FSS) of excitons in semiconductor nanostructures is a key parameter that has significant implications in photon entanglement and polarization conversion between electron spins and photons, relevant to quantum information technology and spintronics. Here, we investigate exciton FSS in self-organized lateral InAs/GaAs quantum-dot molecular structures (QMSs) including laterally aligned double quantum dots (DQDs), quantum-dot clusters (QCs), and quantum rings (QRs), by employing polarization-resolved microphotoluminescence (μPL) spectroscopy. We find a clear trend in FSS between the studied QMSs depending on their geometric arrangements, from a large FSS in the DQDs to a smaller FSS in the QCs and QRs. This trend is accompanied by a corresponding difference in the optical polarization directions of the excitons between these QMSs, namely, the bright-exciton lines are linearly polarized preferably along or perpendicular to the [11̅0] crystallographic axis in the DQDs that also defines the alignment direction of the two constituting QDs, whereas in the QCs and QRs, the polarization directions are randomly oriented. We attribute the observed trend in the FSS to a significant reduction of the asymmetry in the lateral confinement potential of the excitons in the QRs and QCs as compared with the DQDs, as a result of a compensation between the effects of lateral shape anisotropy and piezoelectric field. Our work demonstrates that FSS strongly depends on the geometric arrangements of the QMSs, which effectively tune the degree of the compensation effects and are capable of reducing FSS even in a strained QD system to a limit similar to strain-free QDs. This approach provides a pathway in obtaining high-symmetry quantum emitters desirable for realizing photon entanglement and spintronic devices based on such nanostructures, utilizing an uninterrupted epitaxial growth procedure without special requirements for lattice-matched materials combinations, specific substrate orientations, and nanolithography.

    Ort, förlag, år, upplaga, sidor
    American Chemical Society (ACS), 2015
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-118007 (URN)10.1021/acsnano.5b01387 (DOI)000356988500013 ()25965972 (PubMedID)
    Tillgänglig från: 2015-05-20 Skapad: 2015-05-20 Senast uppdaterad: 2018-09-05
    4. Anomalous spectral dependence of optical polarization and its impact on spin detection in InGaAs/GaAs quantum dots
    Öppna denna publikation i ny flik eller fönster >>Anomalous spectral dependence of optical polarization and its impact on spin detection in InGaAs/GaAs quantum dots
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    2014 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 13, s. 132106-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We show that circularly polarized emission light from InGaAs/GaAs quantum dot (QD) ensembles under optical spin injection from an adjacent GaAs layer can switch its helicity depending on emission wavelengths and optical excitation density. We attribute this anomalous behavior to simultaneous contributions from both positive and negative trions and a lower number of photo-excited holes than electrons being injected into the QDs due to trapping of holes at ionized acceptors and a lower hole mobility. Our results call for caution in reading out electron spin polarization by optical polarization of the QD ensembles and also provide a guideline in improving efficiency of spin light emitting devices that utilize QDs.

    Ort, förlag, år, upplaga, sidor
    American Institute of Physics (AIP), 2014
    Nationell ämneskategori
    Kemi
    Identifikatorer
    urn:nbn:se:liu:diva-112185 (URN)10.1063/1.4897306 (DOI)000343031700033 ()
    Anmärkning

    Funding Agencies|Linkoping University; Swedish Research Council [621-2011-4254]; Japan Society for Promotion of Science [22221007]

    Tillgänglig från: 2014-11-18 Skapad: 2014-11-18 Senast uppdaterad: 2018-09-05
    5. Size dependence of electron spin dephasing in InGaAs quantum dots
    Öppna denna publikation i ny flik eller fönster >>Size dependence of electron spin dephasing in InGaAs quantum dots
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    2015 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, nr 9, s. 093109-Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We investigate ensemble electron spin dephasing in self-assembled InGaAs/GaAs quantum dots (QDs) of different lateral sizes by employing optical Hanle measurements. Using low excitation power, we are able to obtain a spin dephasing time T-2* (in the order of ns) of the resident electron after recombination of negative trions in the QDs. We show that T-2* is determined by the hyperfine field arising from the frozen fluctuation of nuclear spins, which scales with the size of QDs following the Merkulov-Efros-Rosen model. This scaling no longer holds in large QDs, most likely due to a breakdown in the lateral electron confinement. (C) 2015 AIP Publishing LLC.

    Ort, förlag, år, upplaga, sidor
    American Institute of Physics (AIP), 2015
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-117236 (URN)10.1063/1.4914084 (DOI)000351069900054 ()
    Anmärkning

    Funding Agencies|Linkoping University through the Professor Contracts; Swedish Research Council [621-2011-4254, 2008-6582]; Japan Society for Promotion of Science [22221007]

    Tillgänglig från: 2015-04-22 Skapad: 2015-04-21 Senast uppdaterad: 2018-09-05
    6. Spin injection and helicity control of surface spin photocurrent in a three dimensional topological insulator
    Öppna denna publikation i ny flik eller fönster >>Spin injection and helicity control of surface spin photocurrent in a three dimensional topological insulator
    Visa övriga...
    2017 (Engelska)Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 8, artikel-id 15401Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    A three-dimensional (3D) topological insulator (TI) is a unique quantum phase of matter with exotic physical properties and promising spintronic applications. However, surface spin current in a common 3D TI remains difficult to control and the out-of-plane spin texture is largely unexplored. Here, by means of surface spin photocurrent in Bi2Te3 TI devices driven by circular polarized light, we identify the subtle effect of the spin texture of the topological surface state including the hexagonal warping term on the surface current. By exploring the out-of-plane spin texture, we demonstrate spin injection from GaAs to TI and its significant contribution to the surface current, which can be manipulated by an external magnetic field. These discoveries pave the way to not only intriguing new physics but also enriched spin functionalities by integrating TI with conventional semiconductors, such that spin-enabled optoelectronic devices may be fabricated in such hybrid structures.

    Ort, förlag, år, upplaga, sidor
    NATURE PUBLISHING GROUP, 2017
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-138241 (URN)10.1038/ncomms15401 (DOI)000401908900001 ()28530227 (PubMedID)
    Anmärkning

    Funding Agencies|Linkoping University; Swedish Research Council [621-2011-4254, 2016-05091]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Swedish Foundation for Strategic Research [EM11-0002]; Key Program of Natural Science Foundation of China [61334004]; Creative Research Group Project of Natural Science Foundation of China [61321492]; Natural Science Foundation of China [61404153]; Shanghai Pujiang Program [14PJ1410600]

    Tillgänglig från: 2017-06-14 Skapad: 2017-06-14 Senast uppdaterad: 2023-03-28
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  • 10.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Beyer, Jan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Identifying a Generic and Detrimental Role of Fano Resonance in Spin Generation in Semiconductor Nanostructures2021Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 127, nr 12, artikel-id 127401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fano resonance is a fundamental physical process that strongly affects the electronic transport, optical, and vibronic properties of matter. Here, we provide the first experimental demonstration of its profound effect on spin properties in semiconductor nanostructures. We show that electron spin generation in InAs/GaAs quantum-dot structures is completely quenched upon spin injection from adjacent InGaAs wetting layers at the Fano resonance due to coupling of light-hole excitons and the heavy-hole continuum of the interband optical transitions, mediated by an anisotropic exchange interaction. Using a master equation approach, we show that such quenching of spin generation is robust and independent of Fano parameters. This work therefore identifies spin-dependent Fano resonance as a universal spin loss channel in quantum-dot systems with an inherent symmetry-breaking effect.

    Ladda ner fulltext (pdf)
    fulltext
  • 11.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina A.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Phansa, Chanakarn
    University of Cambridge, UK.
    Sandoval-Salinas, Maria E.
    Donostia International Physics Center (DIPC), Spain; Universitat de Barcelona, Spain.
    Casanova, David
    Donostia International Physics Center (DIPC), Spain.
    Myers, William K.
    University of Oxford, UK.
    Greenham, Neil C.
    University of Cambridge, UK.
    Rao, Akshay
    University of Cambridge, UK.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Competition between triplet pair formation and excimer-like recombination controls singlet fission yield2021Ingår i: Cell Reports Physical Science, E-ISSN 2666-3864, Vol. 2, nr 2, artikel-id 100339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ultimate goal for singlet fission is that each photo-excited singlet exciton, S1, will result in two triplet excitons with unity yield. However, the singlet fission is now recognized to be complicated, involving bright/dark excited states of different spin multiplicity. Identifying the role of such states is vital to optimize singlet fission yield but difficult due to their elusive spectral signature. Here, we develop an experimental protocol based on a refined magneto-optical probe to access the fast time evolution of various excited states. In diphenylhexatriene crystal, the S1 is found to undergo two competing processes?to form one of the two dark triplet pair intermediates having different exchange energies or to form a bright state, Sx, exhibiting excimer-like delayed photoluminescence. Our result provides a clear picture of a competition event in singlet fission, which is beneficial for the development and tailoring of singlet fission materials with high yield.

    Ladda ner fulltext (pdf)
    fulltext
  • 12.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Scattering symmetry-breaking induced spin photocurrent from out-of-plane spin texture in a 3D topological insulator2020Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 10, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We theoretically study helicity-dependent photocurrent in a three-dimensional topological insulator Bi2Te3 under elastic scattering of different symmetries. By exploring spin-selective optical transitions and symmetry-breaking scattering, we are able to address the out-of-plane spin texture of the topological helical surface states and to generate directional, spin-polarization tunable photocurrent that is otherwise forbidden for the original C-3v symmetry of the surface. This can be achieved regardless of the Fermi level, even under the condition when the topological states are inaccessible in dark. This work paves the way to robustly explore the out-of-plane spin texture for harvesting opto-spintronic functionalities of topological insulators.

    Ladda ner fulltext (pdf)
    fulltext
  • 13.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Yang, X. J.
    Suzhou QiangMing Optoelect Co Ltd, Peoples R China.
    Murayama, A.
    Hokkaido Univ, Japan.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Effect of a Phonon Bottleneck on Exciton and Spin Generation in Self-Assembled In1-xGaxAs Quantum Dots2018Ingår i: Physical Review Applied, ISSN 2331-7019, Vol. 9, nr 4, artikel-id 044037Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 14.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten. Peking Univ, Peoples R China.
    Kang, N.
    Peking Univ, Peoples R China.
    Electron-hole asymmetric magnetotransport of graphene-colloidal quantum dot device2024Ingår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 653, s. 749-755Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interfacing graphene with other low-dimensional material has gained attentions recently due to its potential to stimulate new physics and device innovations for optoelectronic and electronic applications. Here, we exploit a solution-processed approach to introduce colloidal quantum dot (CQD) to the bilayer graphene device. The magnetotransport properties of the graphene device is drastically altered due to the presence of the CQD potential, leading to the observation of AB-like oscillation in the quantum Hall regime and screening of the intervalley scattering. The anomalous magnetotransport behavior is attributed to the coulombic scattering introduced by the CQDs and is shown to be highly asymmetric depending on the polarity of the transport carriers. These results prove the potential of such flexible method for engineering microscopic scattering process and performance of the graphene device that may lead to intriguing device application in such hybrid system.

  • 15.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten. Chinese Acad Sci, Peoples R China.
    Polojarvi, V
    Tampere Univ, Finland.
    Aho, A.
    Tampere Univ, Finland.
    Isoaho, R.
    Tampere Univ, Finland.
    Hakkarainen, T.
    Tampere Univ, Finland.
    Guina, M.
    Tampere Univ, Finland.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Tuneable Nonlinear Spin Response in a Nonmagnetic Semiconductor2023Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 19, nr 6, artikel-id 064048Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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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  • 16.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Polojarvi, Ville
    Tampere Univ, Finland.
    Hiura, Satoshi
    Hokkaido Univ, Japan.
    Höjer, Pontus
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Aho, Arto
    Tampere Univ, Finland.
    Isoaho, Riku
    Tampere Univ, Finland.
    Hakkarainen, Teemu
    Tampere Univ, Finland.
    Guina, Mircea
    Tampere Univ, Finland.
    Sato, Shino
    Hokkaido Univ, Japan.
    Takayama, Junichi
    Hokkaido Univ, Japan.
    Murayama, Akihiro
    Hokkaido Univ, Japan.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Room-temperature electron spin polarization exceeding 90% in an opto-spintronic semiconductor nanostructure via remote spin filtering2021Ingår i: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893, Vol. 15, s. 475-482Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An exclusive advantage of semiconductor spintronics is its potential for opto-spintronics, which will allow integration of spin-based information processing/storage with photon-based information transfer/communications. Unfortunately, progress has so far been severely hampered by the failure to generate nearly fully spin-polarized charge carriers in semiconductors at room temperature. Here we demonstrate successful generation of conduction electron spin polarization exceeding 90% at room temperature without a magnetic field in a non-magnetic all-semiconductor nanostructure, which remains high even up to 110 degrees C. This is accomplished by remote spin filtering of InAs quantum-dot electrons via an adjacent tunnelling-coupled GaNAs spin filter. We further show that the quantum-dot electron spin can be remotely manipulated by spin control in the adjacent spin filter, paving the way for remote spin encoding and writing of quantum memory as well as for remote spin control of spin-photon interfaces. This work demonstrates the feasibility to implement opto-spintronic functionality in common semiconductor nanostructures. An electron spin polarization of 90% is achieved in a non-magnetic nanostructure at room temperature without magnetic field. This is accomplished by remote spin filtering of InAs quantum-dot electrons via an adjacent tunnelling-coupled GaNAs spin filter.

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  • 17.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Spin injection and detection in semiconductor nanostructures (invited talk)2016Ingår i: 7TH IEEE INTERNATIONAL NANOELECTRONICS CONFERENCE (INEC) 2016, IEEE , 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    We review our recent results from optical spin orientation studies of In(Ga)As/GaAs quantum dots (QD) and QD molecular structures (QMSs), which shed light on some critical issues in spin injection and spin detection in these semiconductor nanostructures.

  • 18.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Spin injection loss in self-assembled InAs/GaAs quantum dot structures from disordered barrier layers2016Ingår i: 2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO), IEEE , 2016, s. 627-629Konferensbidrag (Refereegranskat)
    Abstract [en]

    Semiconductor quantum dot (QD) structures are considered as promising building block for spintronic applications with the advantage of prolonged spin relaxation time owing to 0D character of confined carriers or excitons. However, feasible application is haunted by severe spin injection loss from its adjacent barrier layers and its mechanism is still not fully understood. Here, we show that exciton spin injection in self-assembled InAs/GaAs QD molecular structures (QMSs) is dominated by localized excitons confined within the QD-like regions of the wetting layer (WL) and GaAs barrier layer surrounding QD structures. The origin of spin injection loss is attribute to finite anisotropic exchange interaction (AEI) of the localized excitons subjected to asymmetric confinement potential in the injection layers. As a result, the AEI of the injected excitons and, thus, the spin injection efficiency is determined to be correlated with the overall geometric symmetry of QMSs, which hold strong influence on the confinement potential of the localized excitons in the surrounding barrier layers. Our results shed light on the microscopic origin of the spin injection loss in QD structures. More importantly, they offer a useful guideline to significantly improve spin injection efficiency by optimizing the lateral arrangement of QMSs and overcome a major challenge in the QD based spintronic device applications.

  • 19.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Yang, X. J.
    Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814, Japan.
    Subagyo, A.
    Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814, Japan.
    Sueoka, K.
    Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814, Japan.
    Murayama, A.
    Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814, Japan.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Size dependence of electron spin dephasing in InGaAs quantum dots2015Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, nr 9, s. 093109-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate ensemble electron spin dephasing in self-assembled InGaAs/GaAs quantum dots (QDs) of different lateral sizes by employing optical Hanle measurements. Using low excitation power, we are able to obtain a spin dephasing time T-2* (in the order of ns) of the resident electron after recombination of negative trions in the QDs. We show that T-2* is determined by the hyperfine field arising from the frozen fluctuation of nuclear spins, which scales with the size of QDs following the Merkulov-Efros-Rosen model. This scaling no longer holds in large QDs, most likely due to a breakdown in the lateral electron confinement. (C) 2015 AIP Publishing LLC.

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  • 20.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Filippov, Stanislav
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Oblique Nuclear Quadrupole Interaction in Self-Assembled Structures Based on Semiconductor Quantum Dots2020Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 14, nr 4, artikel-id 044019Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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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  • 21.
    Huang, Yuqing Q.
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Puttisong, Yuttapoom
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Understanding and optimizing spin injection in self-assembled InAs/GaAs quantum-dot molecular structures2016Ingår i: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 9, nr 3, s. 602-611Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semiconductor quantum-dot (QD) structures are promising for spintronic applications owing to strong quenching of spin relaxation processes promoted by carrier and excitons motions. Unfortunately, spin injection efficiency in such nanostructures remains very low and the exact physical mechanism for the spin loss is still not fully understood. Here, we show that exciton spin injection in self-assembled InAs/GaAs QDs and quantum-dot molecular structures (QMSs) is dominated by localized excitons confined within the QD-like regions of the wetting layer (WL) and GaAs barrier layer immediately surrounding QDs and QMSs that in fact lack the commonly believed 2D and 3D character with an extended wavefunction. We identify the microscopic origin of the observed severe spin loss during spin injection as being due to a sizable anisotropic exchange interaction (AEI) of the localized excitons in the WL and GaAs barrier layer, which has so far been overlooked. We find that the AEI of the injected excitons and thus the efficiency of the spin injection processes are correlated with the overall geometric symmetry of the QMSs, as the latter largely defines the anisotropy of the confinement potential of the localized excitons in the surrounding WL and GaAs barrier. These results pave the way for a better understanding of spin injection processes and the microscopic origin of spin loss in QD structures, which in turn provides a useful guideline to significantly improve spin injection efficiency by optimizing the lateral arrangement of the QMSs thereby overcoming a major bottleneck in spintronic device applications utilizing semiconductor QDs.

  • 22.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Song, Y. X.
    Wang, S. M.
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg 412 96, Sweden.
    Buyanova, Irina A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Institutionen för tema. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Institutionen för tema. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Generation of helicity-dependent surface spin photocurrent in 3D topological insulator Bi2Te3 (invited talk)2017Konferensbidrag (Refereegranskat)
  • 23.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Song, Y. X.
    Wang, S. M.
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg 412 96, Sweden.
    Buyanova, Irina A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Institutionen för tema. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Institutionen för tema. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Spin texture and spin injection in a 3D topological insulator (invited talk)2017Konferensbidrag (Refereegranskat)
  • 24.
    Huang, Yuqing
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Song, Y. X.
    Chinese Academic Science, Peoples R China.
    Wang, S. M.
    Chinese Academic Science, Peoples R China; Chalmers, Sweden.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material.
    Spin injection and helicity control of surface spin photocurrent in a three dimensional topological insulator2017Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 8, artikel-id 15401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A three-dimensional (3D) topological insulator (TI) is a unique quantum phase of matter with exotic physical properties and promising spintronic applications. However, surface spin current in a common 3D TI remains difficult to control and the out-of-plane spin texture is largely unexplored. Here, by means of surface spin photocurrent in Bi2Te3 TI devices driven by circular polarized light, we identify the subtle effect of the spin texture of the topological surface state including the hexagonal warping term on the surface current. By exploring the out-of-plane spin texture, we demonstrate spin injection from GaAs to TI and its significant contribution to the surface current, which can be manipulated by an external magnetic field. These discoveries pave the way to not only intriguing new physics but also enriched spin functionalities by integrating TI with conventional semiconductors, such that spin-enabled optoelectronic devices may be fabricated in such hybrid structures.

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  • 25.
    Ji, Fuxiang
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Wang, Feng
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Kobera, Libor
    Czech Acad Sci, Czech Republic.
    Xie, Fangyan
    Sun Yat Sen Univ, Peoples R China.
    Klarbring, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Abbrent, Sabina
    Czech Acad Sci, Czech Republic.
    Brus, Jiri
    Czech Acad Sci, Czech Republic.
    Yin, Chunyang
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci & Technol MISIS, Russia.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Gao, Feng
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Near-Infrared Light-Responsive Cu-Doped Cs2AgBiBr62020Ingår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 30, nr 51, artikel-id 2005521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lead-free halide double perovskites (A(2)B(I)B(III)X(6)) with attractive optical and electronic features are considered to be a promising candidate to overcome the toxicity and stability issues of lead halide perovskites (APbX(3)). However, their poor absorption profiles limit device performance. Here the absorption band edge of Cs(2)AgBiBr(6)double perovskite to the near-infrared range is significantly broadened by developing doped double perovskites, Cs-2(Ag:Cu)BiBr6. The partial replacement of Ag ions by Cu ions in the crystal lattice is confirmed by the X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (ssNMR) measurements. Cu doping barely affects the bandgap of Cs2AgBiBr6; instead it introduces subbandgap states with strong absorption to the near-infrared range. More interestingly, the near-infrared absorption can generate band carriers upon excitation, as indicated by the photoconductivity measurement. This work sheds new light on the absorption modulation of halide double perovskites for future efficient optoelectronic devices.

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  • 26.
    Puttisong, Yuttapoom
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Yang, X. J.
    Hokkaido University, Japan.
    Subagyo, A.
    Hokkaido University, Japan.
    Sueoka, K.
    Hokkaido University, Japan.
    Murayama, A.
    Hokkaido University, Japan.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Funktionella elektroniska material. Linköpings universitet, Tekniska högskolan.
    Anomalous spectral dependence of optical polarization and its impact on spin detection in InGaAs/GaAs quantum dots2014Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 13, s. 132106-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We show that circularly polarized emission light from InGaAs/GaAs quantum dot (QD) ensembles under optical spin injection from an adjacent GaAs layer can switch its helicity depending on emission wavelengths and optical excitation density. We attribute this anomalous behavior to simultaneous contributions from both positive and negative trions and a lower number of photo-excited holes than electrons being injected into the QDs due to trapping of holes at ionized acceptors and a lower hole mobility. Our results call for caution in reading out electron spin polarization by optical polarization of the QD ensembles and also provide a guideline in improving efficiency of spin light emitting devices that utilize QDs.

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  • 27.
    Zhang, Bin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Ji, Fuxiang
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Miao, Xiaohe
    Westlake Univ, Peoples R China.
    Gao, Feng
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Elektroniska och fotoniska material. Linköpings universitet, Tekniska fakulteten.
    Photoactivated Second Harmonic Generation in Centrosymmetric Double Perovskites2023Ingår i: ACS Photonics, E-ISSN 2330-4022, Vol. 10, nr 9, s. 3350-3358Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the firstobservation of second harmonic generation (SHG)from halide double perovskites single crystals, a promising classof materials for low-cost and versatile optoelectronic applications,owing to their enormous structural flexibility and environmental friendliness.We show that the SHG efficiency of these materials with centrosymmetriccrystalline structures critically depends on the measurement temperature.At high temperatures, it is determined by a surface contribution butincreases by up to 3 orders of magnitude at low temperatures (T < 137 K for Cs2NaFeCl6 and T < 250 K for Cs2AgBiBr6) underlight illumination within several minutes. We attribute this enhancementto the build-up of a light-induced electric field within the near-surfaceregion, which generates an additional contribution to the SHG process.This DC electric field is found to be predominantly oriented orthogonallyto the sample surface, as deduced from the six-fold rotational symmetryof the SHG azimuthal pattern. The electric field formation is explainedby photoinduced charge transfer from deep surface-related states totraps in the bulk region or vice versa, mainly driven by diffusion.Furthermore, the inscribed electric field can be maintained for hoursat low temperatures and can only be erased by raising the temperaturedue to carrier detrapping. Our findings, therefore, highlight theimportance of the surface states in double perovskites, which couldbe utilized for enhancing the nonlinear properties of these centrosymmetricmaterials.

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  • 28.
    Zhang, Bin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten. Chinese Academy of Sciences, Shanghai, China.
    Huang, Yuqing
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik.
    Stehr, Jan Eric
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Chen, P.P.
    Chinese Academy of Sciences, Shanghai, China.
    Wang, X. J.
    Chinese Academy of Sciences, Shanghai, China.
    Lu, W
    Chinese Academy of Sciences, Shanghai, China.
    Chen, Weimin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Buyanova, Irina A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska fakulteten.
    Band structure of wurtzite GaBiAs nanowires2019Ingår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, s. 6454-6460Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the first successful growth of wurtzite (WZ) GaBiAs nanowires (NWs) and reveal the effects of Bi incorporation on the electronic band structure by using polarization-resolved optical spectroscopies performed on individual NWs. Experimental evidence of a decrease in the band-gap energy and an upward shift of the topmost three valence subbands upon the incorporation of Bi atoms is provided, whereas the symmetry and ordering of the valence band states remain unchanged, that is, Γ9, Γ7, and Γ7 within the current range of Bi compositions. The extraordinary valence band structure of WZ GaBiAs NWs is explained by anisotropic hybridization and anticrossing between p-like Bi states and the extended valence band states of host WZ GaAs. Moreover, the incorporation of Bi into GaAs is found to significantly reduce the temperature sensitivity of the band-gap energy in WZ GaBiAs NWs. Our work therefore demonstrates that utilizing dilute bismide alloys provides new avenues for band-gap engineering and thus photonic engineering with NWs.

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