| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Fu, Ying, 1964-, et al.
(författare)
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Time-Resolved FDTD and Experimental FTIR Study of Gold Micropatch Arrays for Wavelength-Selective Mid-Infrared Optical Coupling
- 2021
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Ingår i: Sensors. - Basel : MDPI. - 1424-8220. ; 21:15
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Tidskriftsartikel (refereegranskat)abstract
- Infrared radiation reflection and transmission of a single layer of gold micropatch two-dimensional arrays, of patch length ∼1.0μm and width ∼0.2μm, have been carefully studied by a finite-difference time-domain (FDTD) method, and Fourier-transform infrared spectroscopy (FTIR). Through precision design of the micropatch array structure geometry, we achieve a significantly enhanced reflectance (85%), a substantial diffraction (10%), and a much reduced transmittance (5%) for an array of only 15% surface metal coverage. This results in an efficient far-field optical coupling with promising practical implications for efficient mid-infrared photodetectors. Most importantly we find that the propagating electromagnetic fields are transiently concentrated around the gold micropatch array in a time duration of tens of ns, providing us with a novel efficient near-field optical coupling.
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| 3. |
- Hussain, Laiq, 1979-, et al.
(författare)
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SWIR-LWIR Photoluminescence from Sb-based Epilayers Grown on GaAs Substrates by using MBE
- 2018
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Ingår i: Journal of the Korean Physical Society. - : Korean Physical Society. - 0374-4884 .- 1976-8524. ; 73:11, s. 1604-1611
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing Sb-based bulk epilayers on large-scale low-cost substrates such as GaAs for fabricating infrared (IR) photodetectors is presently attracting significant attention worldwide. For this study, three sample series of GaAsxSb1−x, In1−xGaxSb, and InAsxSb1−x with different compositions were grown on semi-insulating GaAs substrates by using molecular beam epitaxy (MBE) and appropriate InAs quantum dots (QDs) as a defect-reduction buffer layer. Photoluminescence (PL) signals from these samples were observed over a wide IR wavelength range from 2 μm to 12 μm in agreement with the expected bandgap, including bowing effects. In particular, interband PL signals from InAsxSb1−x and In1−xGaxSb samples even at room temperature show promising potential for IR photodetector applications.
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| 4. |
- Höglund, Linda, 1974-, et al.
(författare)
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Energy level scheme of InAs/InxGa1-xAs/GaAs quantum-dots-in-a-well infrared photodetector structures
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - Woodbury, NY : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:3, s. 035314-
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Tidskriftsartikel (refereegranskat)abstract
- A thorough investigation of quantum-dots-in-a-well structures for infrared photodetector applications has been performed employing different experimental techniques. The electronic structure of self-assembled InAs quantum dots embedded in an In0.15Ga0.85As/GaAs quantum well (QW) was deduced from photoluminescence (PL) and PL excitation (PLE) spectroscopy. From polarization-dependent PL it was revealed that the quantum dots hold two electron energy levels and two heavy-hole levels. Tunnel capacitance spectroscopy confirmed an electron energy level separation of about 50 meV, and additionally, that the conduction-band ground state and excited state of the dots are twofold and fourfold degenerates, respectively. Intersubband photocurrent spectroscopy, combined with simultaneous interband pumping of the dots, revealed a dominant transition at 150 meV (8.5 mu m) between the ground state of the quantum dots and the excited state of the QW. Results from detailed full three-dimensional calculations of the electronic structure, including effects of composition intermixing and interdot interactions, confirm the experimentally unravelled energy level scheme of the dots and well.
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| 5. |
- Höglund, Linda, 1974-, et al.
(författare)
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Quantum dots-in-a-well infrared photodetectors for long wavelength infrared detection
- 2006
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Ingår i: Proceedings of SPIE. - Bellingham, Wash. : SPIE - International Society for Optical Engineering. - 9780819464996 ; 6401, s. 1-640109
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Konferensbidrag (refereegranskat)abstract
- We report on a quantum dots-in-a-well infrared photodetector (DWELL QDIP) grown by metal organic vapor phase epitaxy. The DWELL QDIP consisted of ten stacked InAs/In0.5Ga0.85As/GaAs QD layers embedded between n-doped contact layers. The density of the QDs was about 9 × 10 10 cm-2 per QD layer. The energy level structure of the DWELL was revealed by optical measurements of interband transitions, and from a comparison with this energy level scheme the origin of the photocurrent peaks could be identified. The main intersubband transition contributing to the photocurrent was associated with the quantum dot ground state to the quantum well excited state transition. The performance of the DWELL QDIPs was evaluated regarding responsivity and dark current for temperatures between 15 K and 77 K. The photocurrent spectrum was dominated by a LWIR peak, with a peak wavelength at 8.4 μm and a full width at half maximum (FWHM) of 1.1 μm. At an operating temperature of 65 K, the peak responsivity was 30 mA/W at an applied bias of 4 V and the dark current was 1.2×10-5 A/cm2. Wavelength tuning from 8.4 μm to 9.5 μm was demonstrated, by reversing the bias of the detector.
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| 6. |
- Höglund, Linda, et al.
(författare)
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Tuning of the detection wavelength in quantum dots-in-a-well infrared photodetectors
- 2008
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Ingår i: Proceedings of SPIE, 6940, Infrared Technology and Applications XXXIV, 694002. - : SPIE. - 9780819471314
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Konferensbidrag (refereegranskat)abstract
- In this study, bias mediated tuning of the detection wavelength within the infrared wavelength region is demonstrated for quantum dots-in-a-well (DWELL) infrared photodetectors. In DWELL structures, intersubband transitions in the conduction band occur from a discrete state in the quantum dot to a subband inthe quantum well. Compared to "conventional" quantum dot infrared photodetectors, where the transitions take place between different discrete bands in thequantum dots, new possibilities to tune the detection wavelength window are opened up, partly by varying the quantum dot energy levels and partly by adjusting the width and composition of the quantum well. In the DWELL structure used, an asymmetric positioning of the InAs quantum dot layer in a 8 nm wide In0.15Ga0.85As/GaAs QW has been applied which enables tuning of the peak detection wavelength within the long wavelength infrared (LWIR; 8 - 14 gm) region. When the applied bias was reversed, a wavelength shift from 8.5 to 9.5 mu m was observed for the peak position in the spectral response. For another DWELL structure, with a well width of 2 nm, the tuning range of the detector could be shifted from the medium wavelength infrared (MWIR; 3-5 mu m) region to the LWIR region. With small changes in the applied bias, the peak detection wavelength could be shifted from 5.1 to 8 mu m. These tuning properties ofDWELL structures could be essential for applications such as modulators and two-colour infrared detection. © (2008) COPYRIGHT SPIE--The International Society for Optical Engineering.
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| 7. |
- Pettersson, Håkan, et al.
(författare)
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Quantum Dots-in-a-Well Infrared Photodetectors-Electronic Structure and Optical Properties
- 2010
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Ingår i: Bulletin of American Physical Society. - : American Physical Society.
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Konferensbidrag (refereegranskat)abstract
- Quantum dots-in-a-well (DWELL) infrared photodetectors is a new class of nanophotonic devices with the potential of significantly increasing the performance and reducing the cost of infrared detectors. Here we present a comprehensive study of DWELL photodetector structures using a variety of optical techniques (PL, PLE, and PC). Complementary tunnel capacitance measurements support the electronic structure obtained from the optical measurements. A detailed energy level scheme based on the experimental findings is presented and compared to theoretical modeling. The presented work show the importance of combining different electrical and optical techniques to obtain a consistent model of complicated quantum structures which is crucial for the development of future nanophotonic devices.
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| 8. |
- Wang, Qin, et al.
(författare)
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MWIR interband transitions in type-II (III) In(GaAl)Sb quantum dots
- 2015
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Konferensbidrag (refereegranskat)abstract
- In this work we present an alternative approach for realizing desired IR devices with appropriate operating wavelengths in the MWIR region utilizing In(GaAl)Sb quantum dots embedded in an InAs matrix grown by MBE. The QDs exhibit spatially indirect interband transitions in a type-II broken bandgap alignment, with a transition energy that can be tuned by bandgap and strain engineering utilizing either the quantum dot size or the incorporation of Ga or (GaAl) into the QDs. Furthermore, the growth of such QDs does not require sophisticated epitaxial designs needed for superlattices or quantum cascade structures regarding large numbers of alternating layers and very exact interfaces. The QD structures are expected to exhibit key advantages for IR devices e.g. higher operating temperature, lower power consumption, size, weight, and cost. The structural and composition properties of designed and grown In(GaAl)Sb QDs were characterized using AFM, SEM, TEM, and XRD. The corresponding optical properties, both in terms of absorption and emission, were analyzed and compared for selected QD samples before and after annealing at 650 °C.
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| 9. |
- Yager, Tom, et al.
(författare)
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Graphene Hybrid Metasurfaces for Mid-Infrared Molecular Sensors
- 2023
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Ingår i: Nanomaterials. - Basel : Multidisciplinary Digital Publishing Institute (MDPI). - 2079-4991. ; 13:14
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Tidskriftsartikel (refereegranskat)abstract
- We integrated graphene with asymmetric metal metasurfaces and optimised the geometry dependent photoresponse towards optoelectronic molecular sensor devices. Through careful tuning and characterisation, combining finite-difference time-domain simulations, electron-beam lithography-based nanofabrication, and micro-Fourier transform infrared spectroscopy, we achieved precise control over the mid-infrared peak response wavelengths, transmittance, and reflectance. Our methods enabled simple, reproducible and targeted mid-infrared molecular sensing over a wide range of geometrical parameters. With ultimate minimization potential down to atomic thicknesses and a diverse range of complimentary nanomaterial combinations, we anticipate a high impact potential of these technologies for environmental monitoring, threat detection, and point of care diagnostics.
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| 10. |
- Zhang, Yazhou, et al.
(författare)
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A Multitask learning model for multimodal sarcasm, sentiment and emotion recognition in conversations
- 2023
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Ingår i: Information Fusion. - Amsterdam : Elsevier. - 1566-2535 .- 1872-6305. ; 93, s. 282-301
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Tidskriftsartikel (refereegranskat)abstract
- Sarcasm, sentiment and emotion are tightly coupled with each other in that one helps the understanding of another, which makes the joint recognition of sarcasm, sentiment and emotion in conversation a focus in the research in artificial intelligence (AI) and affective computing. Three main challenges exist: Context dependency, multimodal fusion and multitask interaction. However, most of the existing works fail to explicitly leverage and model the relationships among related tasks. In this paper, we aim to generically address the three problems with a multimodal joint framework. We thus propose a multimodal multitask learning model based on the encoder–decoder architecture, termed M2Seq2Seq. At the heart of the encoder module are two attention mechanisms, i.e., intramodal (Ia) attention and intermodal (Ie) attention. Ia attention is designed to capture the contextual dependency between adjacent utterances, while Ie attention is designed to model multimodal interactions. In contrast, we design two kinds of multitask learning (MTL) decoders, i.e., single-level and multilevel decoders, to explore their potential. More specifically, the core of a single-level decoder is a masked outer-modal (Or) self-attention mechanism. The main motivation of Or attention is to explicitly model the interdependence among the tasks of sarcasm, sentiment and emotion recognition. The core of the multilevel decoder contains the shared gating and task-specific gating networks. Comprehensive experiments on four bench datasets, MUStARD, Memotion, CMU-MOSEI and MELD, prove the effectiveness of M2Seq2Seq over state-of-the-art baselines (e.g., CM-GCN, A-MTL) with significant improvements of 1.9%, 2.0%, 5.0%, 0.8%, 4.3%, 3.1%, 2.8%, 1.0%, 1.7% and 2.8% in terms of Micro F1. © 2023 Elsevier B.V.
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