| 1. |
- 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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| 2. |
- Nilsson, Henrik, et al.
(författare)
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Unipolar and bipolar operation of InAs/InSb nanowire heterostructure field-effect transistors
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:6
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Tidskriftsartikel (refereegranskat)abstract
- We present temperature dependent electrical measurements on n-type InAs/InSb nanowire heterostructure field-effect transistors. The barrier height of the heterostructure junction is determined to be 220 meV, indicating a broken bandgap alignment. A clear asymmetry is observed when applying a bias to either the InAs or the InSb side of the junction. Impact ionization and band-to-band tunneling is more pronounced when the large voltage drop occurs in the narrow bandgap InSb segment. For small negative gate-voltages, the InSb segment can be tuned toward p-type conduction, which induces a strong band-to-band tunneling across the heterostructucture junction. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3633742]
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| 3. |
- Borg, Mattias, et al.
(författare)
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InAs/GaSb Heterostructure Nanowires for Tunnel Field-Effect Transistors.
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:Online August 24, 2010, s. 4080-4085
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Tidskriftsartikel (refereegranskat)abstract
- InAs/GaSb nanowire heterostructures with thin GaInAs inserts were grown by MOVPE and characterized by electrical measurements and transmission electron microscopy. Down-scaling of the insert thickness was limited because of an observed sensitivity of GaSb nanowire growth to the presence of In. By employing growth interrupts in between the InAs and GaInAs growth steps it was possible to reach an insert thickness down to 25 nm. Two-terminal devices show a diode behavior, where temperature-dependent measurements indicate a heterostructure barrier height of 0.5 eV, which is identified as the valence band offset between the InAs and GaSb. Three-terminal transistor structures with a top-gate positioned at the heterointerface show clear indications of band-to-band tunnelling.
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| 4. |
- Ganjipour, Bahram, et al.
(författare)
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Carrier control and transport modulation in GaSb/InAsSb core/shell nanowires
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:10
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Tidskriftsartikel (refereegranskat)abstract
- We report transport studies of GaSb/InAs core/shell nanowires. It is shown that with increasing InAs shell thickness, it is possible to tune the carrier concentrations and transport in the structures from p-type (core-dominated) to n-type (shell dominated). For nanowires with an intermediate shell thickness (5-7 nm), we show that the transport is ambipolar, such that an applied top-gate potential can provide further control of carrier type and transport path. In this range, the nature of the GaSb-InAs junction also changes from broken gap (semimetal) to staggered (narrow bandgap) with a small decrease in shell thickness. From a device point of view, we demonstrate that the presence of a thin (<3 nm) InAs shell improves p-type GaSb nanowire transistor characteristics. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4749283]
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| 5. |
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| 6. |
- Ganjipour, Bahram, et al.
(författare)
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High current density Esaki tunnel diodes based on GaSb-InAsSb heterostructure nanowires
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:10, s. 4222-4226
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Tidskriftsartikel (refereegranskat)abstract
- We present electrical characterization of broken gap GaSb-InAsSb nanowire heterojunctions. Esaki diode characteristics with maximum reverse current of 1750 kA/cm2 at 0.50 V, maximum peak current of 67 kA/cm2 at 0.11 V, and peak-to-valley ratio (PVR) of 2.1 are obtained at room temperature. The reverse current density is comparable to that of state-of-the-art tunnel diodes based on heavily doped p-n junctions. However, the GaSb-InAsSb diodes investigated in this work do not rely on heavy doping, which permits studies of transport mechanisms in simple transistor structures processed with high-κ gate dielectrics and top-gates. Such processing results in devices with improved PVR (3.5) and stability of the electrical properties.
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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. |
- Svensson, Johannes, et al.
(författare)
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Increased absorption in InAsSb nanowire clusters through coupled optical modes
- 2017
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 110:8
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires can act as efficient light absorbers where waveguide modes are resonant to specific wavelengths. This resonant wavelength can easily be tuned by the nanowire dimensions, but the absorption of infrared radiation requires diameters of hundreds of nm, which is difficult to achieve using epitaxial growth. Here, we demonstrate that infrared absorption in InAsSb nanowires with the diameters of only 140 nm grown on Si substrates can be enhanced resonantly by placing them closely packed in clusters of different sizes. We find that coating the nanowires with a dielectric to optically connect them results in an efficient absorption diameter far exceeding the diameter of the constituent nanowires and that the cut-off wavelength is redshifted with an increasing cluster diameter. Numerical simulations are in agreement with the experimental results and demonstrate that if nanowires are positioned in clusters, a peak absorptance of 20% is possible at 5.6 μm with only 3% surface coverage. This absorptance is 200 times higher than for wires placed in an equidistant pattern. Our findings have direct implications for the design of efficient nanowire based photodetectors and solar cells.
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| 9. |
- Wernersson, Lars-Erik, et al.
(författare)
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Metalorganic vapor phase epitaxy-grown GaP/GaAs/GaP and GaAsP/GaAs/GaAsP n-type resonant tunnelling diodes
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:10, s. 1841-1843
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Tidskriftsartikel (refereegranskat)abstract
- We have studied GaP/GaAs/GaP and GaAsxP1-x/GaAs/GaAsxP1-x double-barrier resonant tunnelling diodes grown by metalorganic vapor phase epitaxy. We find that GaP tensile strained barriers in GaP/GaAs/GaP diodes may be grown with a barrier thickness below the critical thickness of about 12 monolayers. However, a corrugation of the strained barrier is observed by transmission electron microscopy. This variation may explain the low peak-to-valley ratio of the diodes (about 2). In contrast, GaAsxP1-x/GaAs/GaAsxP1-x resonant tunnelling diodes have been grown with a homogeneous thickness of the barriers, consequently showing a substantially improved electrical performance compared to the GaP diodes with peak-to-valley ratios >5.
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| 10. |
- Aghaeipour, Mahtab, et al.
(författare)
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Comparative study of absorption efficiency of inclined and vertical InP nanowires
- 2017
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Ingår i: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VI. - Bellingham, WA : SPIE - International Society for Optical Engineering. - 9781510606401 ; 10099
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Konferensbidrag (refereegranskat)abstract
- Geometrically designed III-V nanowire arrays are promising candidates for optoelectronics due to their possibility to excite nanophotonic resonances in absorption spectra. Strong absorption resonances can be obtained by proper tailoring of nanowire diameter, length and pitch. Such enhancement of the light absorption is, however, accompanied by undesired resonance dips at specific wavelengths. In this work, we theoretically show that tilting of the nanowires mitigates the absorption dips by exciting strong Mie resonances. In particular, we derive a theoretical optimum inclination angle of about 30 degrees at which the inclined nanowires gain 8% in absorption efficiency compared to vertically standing nanowires in a spectral region matching the intensity distribution of the sun. The enhancement is due to engineering the excited modes inside the nanowires regarding the symmetry properties of the nanowire/light system without increasing the absorbing material. We expect our results to be important for nanowire-based photovoltaic applications. © 2017 SPIE.
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