| 1. |
- Xu, Tao, et al.
(författare)
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Faceting, composition and crystal phase evolution in III-V antimonide nanowire heterostructures revealed by combining microscopy techniques
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:9
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Tidskriftsartikel (refereegranskat)abstract
- III-V antimonide nanowires are among the most interesting semiconductors for transport physics, nanoelectronics and long-wavelength optoelectronic devices due to their optimal material properties. In order to investigate their complex crystal structure evolution, faceting and composition, we report a combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) study of gold-nucleated ternary InAs/InAs1-xSbx nanowire heterostructures grown by molecular beam epitaxy. SEM showed the general morphology and faceting, TEM revealed the internal crystal structure and ternary compositions, while STM was successfully applied to characterize the oxide-free nanowire sidewalls, in terms of nanofaceting morphology, atomic structure and surface composition. The complementary use of these techniques allows for correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth. The addition of even a minute amount of Sb to InAs changes the crystal structure from perfect wurtzite to perfect zinc blende, via intermediate stacking fault and pseudo-periodic twinning regimes. Moreover, the addition of Sb during the axial growth of InAs/InAs1-xSbx heterostructure nanowires causes a significant conformal lateral overgrowth on both segments, leading to the spontaneous formation of a core-shell structure, with an Sb-rich shell.
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| 2. |
- Astromskas, Gvidas, et al.
(författare)
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Doping Incorporation in InAs nanowires characterized by capacitance measurements
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108
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Tidskriftsartikel (refereegranskat)abstract
- Sn and Se doped InAs nanowires are characterized using a capacitance-voltage technique where the threshold voltages of nanowire capacitors with different diameter are determined and analyzed using an improved radial metal-insulator-semiconductor field-effect transistor model. This allows for a separation of doping in the core of the nanowire from the surface charge at the side facets of the nanowire. The data show that the doping level in the InAs nanowire can be controlled on the level between 2×1018 to 1×1019 cm−3, while the surface charge density exceeds 5×1012 cm−2 and is shown to increase with higher dopant precursor molar fraction.
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| 3. |
- Astromskas, Gvidas, et al.
(författare)
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Temperature and frequency characterization of InAs nanowire and HfO2 interface using capacitance-voltage method
- 2011
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Ingår i: Microelectronic Engineering. - : Elsevier BV. - 1873-5568 .- 0167-9317. ; 88:4, s. 444-447
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Konferensbidrag (refereegranskat)abstract
- InAs/HfO2 nanowire capacitors using capacitance-voltage (CV) measurements are investigated in the range of 10 kHz to 10 MHz. The capacitors are based on vertical nanowire arrays that are coated with an 8 nm-thick HfO2 layer by atomic layer deposition. CV characteristics are measured at temperatures in the range between -140 and 40 degrees C and the CV characteristics for nanowires with different Sn and Se n-type doping levels are compared. The comparison of the data at various doping levels points towards large number of traps for highly doped samples, caused by the preferential dopant precursor incorporation at the nanowire surface. We also evaluate the frequency dispersion of the accumulation capacitance and determine values below 2% with weak temperature dependence, indicating the existence of border traps in these nanowire capacitors. (C) 2010 Elsevier B.V. All rights reserved.
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| 4. |
- Astromskas, Gvidas, et al.
(författare)
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Temperature dependence of GaSb overgrowth of tungsten on GaSb (001) substrates using MOVPE
- 2008
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Ingår i: 20th International Conference on Indium Phosphide and Related Materials, 2008. IPRM 2008. - 1092-8669. ; , s. 354-356
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Konferensbidrag (refereegranskat)abstract
- We demonstrate GaSb overgrowth over tungsten patterns and that selective area epitaxy is achievable in the W/GaSb system. By controlling the facet growth at low temperatures, it is possible to embed a metal grating in a thin layer.
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| 5. |
- Berg, Alexander, et al.
(författare)
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Growth and optical properties of InxGa1−xP nanowires synthesized by selective-area epitaxy
- 2017
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Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 10:2, s. 672-682
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Tidskriftsartikel (refereegranskat)abstract
- Ternary III–V nanowires (NWs) cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield, reproducibility, and tunable optical absorption. Here, we report on successful selective-area epitaxy of metal-particle-free vertical InxGa1−xP NW arrays using metal–organic vapor phase epitaxy and detail their optical properties. A systematic growth study establishes the range of suitable growth parameters to obtain uniform NW growth over a large array. The optical properties of the NWs were characterized by room-temperature cathodoluminescence spectroscopy. Tunability of the emission wavelength from 870 nm to approximately 800 nm was achieved. Transmission electron microscopy and energy dispersive X-ray measurements performed on cross-section samples revealed a pure wurtzite crystal structure with very few stacking faults and a slight composition gradient along the NW growth axis. [Figure not available: see fulltext.]
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| 6. |
- Bolinsson, Jessica, et al.
(författare)
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Wurtzite-zincblende superlattices in InAs nanowires using a supply interruption method.
- 2011
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 22:26
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Tidskriftsartikel (refereegranskat)abstract
- Crystal phase control in single III-V semiconductor nanowires has emerged recently as an important challenge and possible complement to conventional bandgap engineering in single material systems. Here we investigate a supply interruption method for precise crystal phase control in single nanowires. The nanowires are grown by metalorganic vapor phase epitaxy using gold particles as seeds and are analyzed by transmission electron microscopy. It is observed that wurtzite segments with controlled length and position can be inserted on demand into a pure InAs zincblende nanowire. The interface between wurtzite and zincblende segments can be made atomically sharp and the segments can be made only a few bilayers in thickness. The growth mechanisms, applicability and limitations of the technique are presented and discussed.
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| 7. |
- Borg, Mattias, et al.
(författare)
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Characterization of GaSb nanowires grown by MOVPE
- 2008
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Ingår i: Journal of Chrystal Growth. - : Elsevier BV. - 0022-0248. ; 310:23, s. 5119-5122
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Konferensbidrag (refereegranskat)abstract
- We report the growth and characterization of GaSb nanowires grown by MOVPE. The structural properties of the nanowires are investigated by the means of transmission electron microscopy, X-ray diffraction and single nanowire photoluminescence. The measurements confirm a high material quality in the GaSb nanowires. Also, a back-gated nanowire transistor structure is used to extract values for the polarity and resistivity of the GaSb. Finally, a simple kinetic model is presented to explain the non-linear time dependence of the GaSb nanowire growth. (C) 2008 Elsevier B.V. All rights reserved.
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| 8. |
- Borg, Mattias, et al.
(författare)
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GaAs/GaSb nanowire heterostructures grown by MOVPE
- 2008
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 310:18, s. 4115-4121
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Tidskriftsartikel (refereegranskat)abstract
- We report Au-assisted growth of GaAs/GaSb nanowire heterostructures on GaAs(1 1 1)B-substrates by metal-organic vapor phase epitaxy. The growth is studied at various precursor molar fractions and temperatures, in order to optimize the growth conditions for the GaSb nanowire segment. In contrast to most other III-V nanowire systems, the GaSb nanowire growth is Group V-limited under most conditions. We found that depending on the TMSb molar fraction, the seed particle is either supersaturated AuGa or AuGa2 during GaSb growth. The high Ga content in the particle gives a characteristic diameter increase between the GaAs and GaSb segment. From TEM and XEDS measurements we conclude that the GaSb nanowire growth occurs along either the AuGa-GaSb or AuGa2-GaSb pseudo-binaries of the Au-Ga-Sb ternary phase diagram. Finally, the GaSb nanowires exhibit untapered radial growth on the {1 (1) over bar 0} side facets. (C) 2008 Elsevier B.V. All rights reserved.
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| 9. |
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| 10. |
- Borg, Mattias, et al.
(författare)
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MOVPE Growth and Structural Characterization of Extremely Lattice-Mismatched InP-InSB Nanowire Heterostructures
- 2009
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Ingår i: 2009 IEEE 21st International Conference On Indium Phosphide & Related Materials (IPRM). - 1092-8669. ; , s. 249-252
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Konferensbidrag (refereegranskat)abstract
- We present a growth study and structural characterization of InP-InSb nanowire heterostructures. In contrast to planar epitaxy, this heterostructure can be realized in nanowires without the formation of dislocations, despite an extreme lattice-mismatch (10.4%). We obtain high crystal quality in the InSb nanowires, confirmed by a narrow 111 reflection peak measured by XRD. Additionally, the diameter dependence of the nanowire growth rate was investigated. An original competition between surface growth and nanowire growth is found, which can be controlled by varying the nanowire surface coverage. Finally, HRTEM and X-EDS investigations reveal that the InSb nanowire is always defect-free zinc-blende, and that the InP-InSb heterointerface is free from misfit dislocations, although single twin planes are common.
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| 11. |
- Caroff, Philippe, et al.
(författare)
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Controlled polytypic and twin-plane superlattices in iii-v nanowires.
- 2009
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3395 .- 1748-3387. ; 4:1, s. 50-55
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires show promise for use in nanoelectronics, fundamental electron transport studies, quantum optics and biological sensing. Such applications require a high degree of nanowire growth control, right down to the atomic level. However, many binary semiconductor nanowires exhibit a high density of randomly distributed twin defects and stacking faults, which results in an uncontrolled, or polytypic, crystal structure. Here, we demonstrate full control of the crystal structure of InAs nanowires by varying nanowire diameter and growth temperature. By selectively tuning the crystal structure, we fabricate highly reproducible polytypic and twin-plane superlattices within single nanowires. In addition to reducing defect densities, this level of control could lead to bandgap engineering and novel electronic behaviour.
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| 12. |
- Caroff, Philippe, et al.
(författare)
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Crystal Phases in III-V Nanowires: From Random Toward Engineered Polytypism
- 2011
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X. ; 17:4, s. 829-846
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Tidskriftsartikel (refereegranskat)abstract
- III-V nanowires (NWs) are promising for a wide range of applications, ranging from optics to electronics, energy, and biological sensing. The structural quality of NWs is of paramount importance for the performance of such future NW-based devices. Random structural defects and polytypism occur naturally in semiconductor NWs, but progress both on the theoretical understanding and experimental control have been achieved recently. Here, we review progress towards the realization of perfect wurtzite and zinc-blende phases in III-VNWs, eventually leading to true phase engineering in single NWs.
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| 13. |
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| 14. |
- Caroff, Philippe, et al.
(författare)
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InAs film grown on Si(111) by Metalorganic Vapor Phase Epitaxy
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 100, s. 042017-042017
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Konferensbidrag (refereegranskat)abstract
- We report the successful growth of high quality InAs films directly on Si( 111) by Metal Organic Vapor Phase Epitaxy. A nearly mirror-like and uniform InAs film is obtained at 580 C for a thickness of 2 mu m. We measured a high value of the electron mobility of 5100 cm(2)/Vs at room temperature. The growth is performed using a standard two-step procedure. The influence of the nucleation layer, group V flow rate, and layer thickness on the electrical and morphological properties of the InAs film have been investigated. We present results of our studies by Atomic Force Microscopy, Scanning Electron Microscopy, electrical Hall/van der Pauw and structural X-Ray Diffraction characterization.
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| 15. |
- Caroff, Philippe, et al.
(författare)
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InSb heterostructure nanowires: MOVPE growth under extreme lattice mismatch.
- 2009
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:49
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the growth of InSb-based nanowire heterostructures by metalorganic vapour phase epitaxy and use it to integrate InSb on extremely lattice-mismatched III-V nanowire templates made of InAs, InP, and GaAs. Influence of temperature, V/III ratio, and diameter are investigated in order to investigate the growth rate and morphology. The range of growth temperatures used for InSb nanowire growth is very similar to that used for planar growth due to the nature of the precursor decomposition. This makes optimization of growth parameters very important, and more difficult than for most other nanowire III-V materials. Analysis of the InSb nanowire epitaxial quality when grown on InAs, InP, and GaAs, along with InSb segment and particle compositions are reported. This successful direct integration of InSb nanowires, on nanowire templates with unprecedented strain levels show great promise for fabrication of vertical InSb devices.
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| 16. |
- Churchill, H. O. H., et al.
(författare)
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Superconductor-nanowire devices from tunneling to the multichannel regime: Zero-bias oscillations and magnetoconductance crossover
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:24
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Tidskriftsartikel (refereegranskat)abstract
- We present transport measurements in superconductor-nanowire devices with a gated constriction forming a quantum point contact. Zero-bias features in tunneling spectroscopy appear at finite magnetic fields and oscillate in amplitude and split away from zero bias as a function of magnetic field and gate voltage. A crossover in magnetoconductance is observed: Magnetic fields above similar to 0.5 T enhance conductance in the low-conductance (tunneling) regime but suppress conductance in the high-conductance (multichannel) regime. We consider these results in the context of Majorana zero modes as well as alternatives, including the Kondo effect and analogs of 0.7 structure in a disordered nanowire.
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| 17. |
- Conesa-Boj, Sonia, et al.
(författare)
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Vertical "III-V" V-Shaped Nanomembranes Epitaxially Grown on a Patterned Si[001] Substrate and Their Enhanced Light Scattering
- 2012
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 6:12, s. 10982-10991
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new form of III-IV compound semiconductor nanostructures growing epitaxially as vertical V-shaped nanomembranes on Si(001) and study their light-scattering properties. Precise position control of the InAs nanostructures in regular arrays is demonstrated by bottom-up synthesis using molecular beam epitaxy in nanoscale apertures on a SiO2 mask. The InAs V-shaped nanomembranes are found to originate from the two opposite facets of a rectangular pyramidal island nucleus and extend along two opposite < 111 > B directions, forming flat {110} walls. Dark-field scattering experiments, in combination with light-scattering theory, show the presence of distinctive shape-dependent optical resonances significantly enhancing the local intensity of incident electromagnetic fields over tunable spectral regions. These new nanostructures could have interesting potential in nanosensors, infrared light emitters, and nonlinear optical elements.
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| 18. |
- Deng, Mingtang, et al.
(författare)
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Parity independence of the zero-bias conductance peak in a nanowire based topological superconductor-quantum dot hybrid device.
- 2014
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4
-
Tidskriftsartikel (refereegranskat)abstract
- We explore the signatures of Majorana fermions in a nanowire based topological superconductor-quantum dot-topological superconductor hybrid device by charge transport measurements. At zero magnetic field, well-defined Coulomb diamonds and the Kondo effect are observed. Under the application of a finite, sufficiently strong magnetic field, a zero-bias conductance peak structure is observed. It is found that the zero-bias conductance peak is present in many consecutive Coulomb diamonds, irrespective of the even-odd parity of the quasi-particle occupation number in the quantum dot. In addition, we find that the zero-bias conductance peak is in most cases accompanied by two differential conductance peaks, forming a triple-peak structure, and the separation between the two side peaks in bias voltage shows oscillations closely correlated to the background Coulomb conductance oscillations of the device. The observed zero-bias conductance peak and the associated triple-peak structure are in line with Majorana fermion physics in such a hybrid topological system.
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| 19. |
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| 20. |
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| 21. |
- Dick Thelander, Kimberly, et al.
(författare)
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Control of III-V nanowire crystal structure by growth parameter tuning
- 2010
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate the variation of the crystal structure of gold-seeded III-V nanowires with growth parameters, in order to gain a cohesive understanding of these effects. We investigate six III-V materials: GaAs, InAs, GaP, InP, GaSb and InSb, over a variation of growth conditions. All six of these materials exhibit a cubic zinc blende structure in bulk, but twin planes and stacking faults, as well as a hexagonal wurtzite structure, are commonly observed in nanowires. Parameters which may affect the crystal structure include growth temperature and pressure, precursor molar fraction and V/III ratio, nanowire diameter and surface density, and impurity atoms. We will focus on temperature, precursor molar fraction and V/III ratio. Our observations are compared to previous reports in the literature of the III-V nanowire crystal structure, and interpreted in terms of existing models. We propose that changes in the crystal structure with growth parameters are directly related to changes in the stable side facets.
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| 22. |
- Dick Thelander, Kimberly, et al.
(författare)
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Crystal Phase Engineering in Single InAs Nanowires.
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:9, s. 3494-3499
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Tidskriftsartikel (refereegranskat)abstract
- Achieving phase purity and control in III-V nanowires is a necessity for future nanowire-based device applications. Many works have focused on cleaning specific crystal phases of defects such as twin planes and stacking faults, using parameters such as diameter, temperature, and impurity incorporation. Here we demonstrate an improved method for crystal phase control, where crystal structure variations in single InAs nanowires are designed with alternating wurtzite (WZ) and zinc blende (ZB) segments of precisely controlled length and perfect interfaces. We also demonstrate the inclusion of single twin planes and stacking faults with atomic precision in their placement, designed ZB quantum dots separated by thin segments of WZ, acting as tunnel barriers for electrons, and structural superlattices (polytypic and twin plane). Finally, we present electrical data to demonstrate the applicability of these designed structures to investigation of fundamental properties. From electrical measurements we observe clear signatures of controlled structural quantum dots in nanowires. This method will be directly applicable to a wide range of nanowire systems.
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| 23. |
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| 24. |
- Dick Thelander, Kimberly, et al.
(författare)
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Metal-seeded growth of III-V semiconductor nanowires: towards gold-free synthesis.
- 2014
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 6:6, s. 3006-3021
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires composed of III-V materials have enormous potential to add new functionality to electronics and optical applications. However, integration of these promising structures into applications is severely limited by the current near-universal reliance on gold nanoparticles as seeds for nanowire fabrication. Although highly controlled fabrication is achieved, this metal is entirely incompatible with the Si-based electronics industry. In this Feature we review the progress towards developing gold-free bottom-up synthesis techniques for III-V semiconductor nanowires. Three main categories of nanowire synthesis are discussed: selective-area epitaxy, self-seeding and foreign metal seeding, with main focus on the metal-seeded techniques. For comparison, we also review the development of foreign metal seeded synthesis of silicon and germanium nanowires. Finally, directions for future development and anticipated important trends are discussed. We anticipate significant development in the use of foreign metal seeding in particular. In addition, we speculate that multiple different techniques must be developed in order to replace gold and to provide a variety of nanowire structures and properties suited to a diverse range of applications.
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| 25. |
- Dick Thelander, Kimberly, et al.
(författare)
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Parameter space mapping of InAs nanowire crystal structure
- 2011
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 29:4
-
Tidskriftsartikel (refereegranskat)abstract
- Crystal structure and defects have been shown to have a strong impact on III-V nanowire properties. Recently, it was demonstrated that the issue of random stacking and polytypism in semiconductor nanowires can often be controlled using accessible growth parameters (such as temperature, diameter, and V/III ratio). In addition, it has been shown that crystal phase can be tuned selectively between cubic zinc blende and hexagonal wurtzite within individual nanowires of III-V materials such as InAs. In order for such results to be generally applied to different growth setups, it is necessary to fully explore and understand the trends governing crystal phase dependencies on all accessible growth parameters, including how they relate to each other. In this study, the authors have systematically investigated the influence of temperature, diameter, V/III ratio, and total mass flow on the crystal structure of InAs nanowires grown by metal-organic vapor phase epitaxy over a broad parameter range. The authors observed that each of these accessible parameters can affect the resulting crystal structure, and that the trends for each parameter are affected by the magnitude of the others. The authors also noted that most of the parameter dependencies are nonlinear and, in fact, exhibit threshold values at which structure changes discontinuously. By optimizing each of the growth parameters, it is shown that pure ZB or pure WZ phase can be achieved for several different sets of growth conditions. The roles of nucleation kinetics, thermodynamics, and precursor chemistry are also discussed to compare the results to current nanowire growth models. The results in this work should facilitate comparison of data and transfer of knowledge between different growth systems and techniques, which, in turn, should lead to greater understanding of polytypism in nanowires and greater control and freedom in nanowire crystal phase engineering. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3593457]
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| 26. |
- Egard, Mikael, et al.
(författare)
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60 GHz Wavelet Generator for Impulse Radio Applications
- 2009
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Ingår i: European Microwave Conference, 2009. EuMC 2009. - 9781424447480 ; , s. 1908-1911, s. 234-237
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Konferensbidrag (refereegranskat)abstract
- A wavelet generator producing 100 ps short pulses at 60 GHz is presented. The wavelet generator consists of a gated tunnel diode (GTD) integrated in parallel with an inductor. This forms a negative differential conductance (NDC) oscillator with the ability to switch the NDC property on and off, which makes it possible to generate short pulses. In the experiments described, the wavelet generator drives a 50 Omega load and delivers 206 mV(pp) when generating 97 ps short pulses at 60 GHz. It Is demonstrated that it is possible to generate pulses of different length and phase. An explanation of the almost instantaneously startup and decay lapse of the oscillator, including generation of signals with opposite phase, is presented. This novel circuit may find use in ultra-wideband impulse radio communication.
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| 27. |
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| 28. |
- Eriksson Linsmeier, Cecilia, et al.
(författare)
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Nanowire Biocompatibility in the Brain - Looking for a Needle in a 3D Stack.
- 2009
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9:12, s. 4184-4190
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the brain-tissue response to nanowire implantations in the rat striatum after 1, 6, and 12 weeks using immunohistochemistry. The nanowires could be visualized in the scar by confocal microscopy (through the scattered laser light). For the nanowire-implanted animals, there is a significant astrocyte response at week 1 compared to controls. The nanowires are phagocytized by ED1 positive microglia, and some of them are degraded and/or transported away from the brain.
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| 29. |
- Fan, Dingxun, et al.
(författare)
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Formation of long single quantum dots in high quality InSb nanowires grown by molecular beam epitaxy
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:36, s. 14822-14828
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Tidskriftsartikel (refereegranskat)abstract
- We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO2 substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudinal size of similar to 700 nm. In the few-electron regime, the quantum levels in the QDs are resolved and the Lande g-factors extracted for the quantum levels from the magnetotransport measurements are found to be strongly level-dependent and fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted from the magnetic field evolutions of a ground state and its neighboring excited state in an InSb nanowire QD and is on the order of similar to 300 mu eV. Our results establish that the MBE-grown InSb nanowires are of high crystal quality and are promising for the use in constructing novel quantum devices, such as entangled spin qubits, one-dimensional Wigner crystals and topological quantum computing devices.
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| 30. |
- Gorji, Sepideh, et al.
(författare)
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Demonstration of Defect-Free and Composition Tunable Ga(x)In(1-x)Sb Nanowires.
- 2012
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 12:9, s. 4914-4919
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Tidskriftsartikel (refereegranskat)abstract
- The Ga(x)In(1-x)Sb ternary system has many interesting material properties, such as high carrier mobilities and a tunable range of bandgaps in the infrared. Here we present the first report on the growth and compositional control of Ga(x)In(1-x)Sb material grown in the form of nanowires from Au seeded nanoparticles by metalorganic vapor phase epitaxy. The composition of the grown Ga(x)In(1-x)Sb nanowires is precisely controlled by tuning the growth parameters where x varies from 1 to ∼0.3. Interestingly, the growth rate of the Ga(x)In(1-x)Sb nanowires increases with diameter, which we model based on the Gibbs-Thomson effect. Nanowire morphology can be tuned from high to very low aspect ratios, with perfect zinc blende crystal structure regardless of composition. Finally, electrical characterization on nanowire material with a composition of Ga(0.6)In(0.4)Sb showed clear p-type behavior.
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| 31. |
- Gorji, Sepideh, et al.
(författare)
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Morphology and composition controlled GaxIn1-xSb nanowires: understanding ternary antimonide growth.
- 2014
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 6:2, s. 1086-1092
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Tidskriftsartikel (refereegranskat)abstract
- Antimonide-based nanowires represent an important new class of material with great promise for both fundamental physics studies and various device applications. We report a comprehensive study on understanding the growth behaviour of GaxIn1-xSb nanowires on GaAs substrates using Au nanoparticles. First, the effect of growth parameters on the morphology and composition of GaxIn1-xSb nanowires is extensively studied over the entire compositional range (from 3 to ∼100% of In). Second, the obtained compositional results are explained by a kinetic model, suggesting an Arrhenius-type behavior for the trimethylindium (TMIn) precursor. Third, the particle composition is fully investigated and the implications for growth are discussed with reference to our calculated Au-Ga-In phase diagram. Fourth, a mechanism is presented to explain the temperature-dependent morphology and radial growth of the GaxIn1-xSb nanowires. Finally, we demonstrate homogeneous compositions in both axial and radial directions and the nanowires remain entirely twin-free zinc blende. The understanding gained from this study together with the potential to precisely tailor the band gap, wavelength and carrier mobilities allows fabrication of various GaxIn1-xSb-based nanowire devices.
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| 32. |
- Johansson, Jonas, et al.
(författare)
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Combinatorial Approaches to Understanding Polytypism in III-V Nanowires.
- 2012
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 6:7, s. 6142-6149
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Tidskriftsartikel (refereegranskat)abstract
- Polytypism in III-V semiconductor nanowires is a topic that has received considerable attention in recent years. Achieving a pure nanowire crystal phase requires well-controlled and advanced parameter tuning for most III-V materials. Additionally, the new and unusual phases sometimes observed may present unique material properties if they can be controllably fabricated. With the prospect of using nanowires in applications within several different fields (including electronics, photonics, and life science), theoretical models are necessary to explain experimental trends and to attain a high level of crystal phase control. At present, there is no theoretical model (or combination of models) that fully explains how and why nanowire crystal structures commonly include several different polytypes. Here we use combinatorics and interlayer interactions to include higher order polytypes (4H and 6H) with the aim to explain nanowire crystal structure beyond the well-investigated zinc blende-wurtzite polytypism. Predictions from our theoretical models compare well with experimental results.
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| 33. |
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| 34. |
- Johansson, Jonas, et al.
(författare)
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Diameter Dependence of the Wurtzite-Zinc Blende Transition in InAs Nanowires
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:9, s. 3837-3842
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the crystal structure of InAs nanowires call be controlled with nanowire diameter and growth temperature. At small diameters, the nanowires exhibit a wurtzite Structure. As the diameter is increased, there is a crossover to the zinc blende structure. The crossover is less sharp at lower growth temperature and L, the crossover diameter decreases as the growth temperature is increased. We explain these results with classical nucleation theory. The strong diameter dependence is accounted for by including the Gibbs-Thomson effect in the chemical potential.
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| 35. |
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| 36. |
- Kriegner, Dominik, et al.
(författare)
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Unit Cell Structure of Crystal Polytypes in InAs and InSb Nanowires
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:4, s. 1483-1489
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Tidskriftsartikel (refereegranskat)abstract
- The atomic distances in hexagonal polytypes of III-V compound semiconductors differ from the values expected from simply a change of the stacking sequence of (111) lattice planes. While these changes were difficult to quantify so far, we accurately determine the lattice parameters of zinc blende, wurtzite, and 4H polytypes for InAs and InSb nanowires, using X-ray diffraction and transmission electron microscopy. The results are compared to density functional theory calculations. Experiment and theory show that the occurrence of hexagonal bilayers tend to strech the distances of atomic layers parallel to the c-axis and to reduce the in-plane distances compared to those in zinc blende. The change of the lattice parameters scales linearly with the hexagonality of the polytype, defined as the fraction of bilayers with hexagonal character within one unit cell.
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| 37. |
- Nakkar, A, et al.
(författare)
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Optical properties and morphology of InAs/InP (113)B surface quantum dots
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:23, s. 3-231911
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Tidskriftsartikel (refereegranskat)abstract
- We report on long-wavelength photoluminescence (PL) emission at room temperature from self-organized InAs surface quantum dots grown by gas-source molecular beam epitaxy on a GaInAsP/InP (113)B substrate. The influence of arsenic pressure conditions during growth on the PL emission of surface quantum dots is detailed as well as oxide/contamination layer formation after growth. Experimental results are in good agreement with six-band k.p theory in the envelope function approximation.
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| 38. |
- Nilsson, Henrik, et al.
(författare)
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Correlation-induced conductance suppression at level degeneracy in a quantum dot.
- 2010
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Ingår i: Physical Review Letters. - 1079-7114. ; 104:18
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Tidskriftsartikel (refereegranskat)abstract
- The large, level-dependent g factors in an InSb nanowire quantum dot allow for the occurrence of a variety of level crossings in the dot. While we observe the standard conductance enhancement in the Coulomb blockade region for aligned levels with different spins due to the Kondo effect, a vanishing of the conductance is found at the alignment of levels with equal spins. This conductance suppression appears as a canyon cutting through the web of direct tunneling lines and an enclosed Coulomb blockade region. In the center of the Coulomb blockade region, we observe the predicted correlation-induced resonance. Our findings are supported by numerical and analytical calculations.
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| 39. |
- Nilsson, Henrik, et al.
(författare)
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Giant, level-dependent g factors in InSb nanowire quantum dots.
- 2009
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9:9, s. 3151-3156
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Tidskriftsartikel (refereegranskat)abstract
- We report on magnetotransport measurements on InSb nanowire quantum dots. The measurements show that the quantum levels of the InSb quantum dots have giant g factors, with absolute values up to approximately 70, the largest value ever reported for semiconductor quantum dots. We also observe that the values of these g factors are quantum level dependent and can differ strongly between different quantum levels. The presence of giant g factors indicates that considerable contributions from the orbital motion of electrons are preserved in the measured InSb nanowire quantum dots, while the level-to-level fluctuations arise from spin-orbit interaction. We have deduced a value of Delta(SO) = 280 mueV for the strength of spin-orbit interaction from an avoided level crossing between the ground state and first excited state of an InSb nanowire quantum dot with a fixed number of electrons.
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| 40. |
- Nilsson, Henrik, et al.
(författare)
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InSb Nanowire Field-Effect Transistors and Quantum-Dot Devices
- 2011
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X. ; 17:4, s. 907-914
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Tidskriftsartikel (refereegranskat)abstract
- The authors present fabrication and electrical measurements of InSb nanowire field-effect transistors (FETs) and quantum dots. The devices are made on a SiO2-capped Si substrate from InSb segments of InAs/InSb heterostructured nanowires, which are grown by metalorganic vapor phase epitaxy. For the FETs, both single- and dual-gate devices are fabricated. The Si substrate is employed as the back gate in both the single-and dual-gate devices, while a top metal gate is employed as a second gate in the dual-gate devices. This top gate is made either as a global gate or as a local finger gate by using a thin HfO2 layer grown by atomic layer deposition as a gate dielectric. The measurements reveal that the fabricated devices show the desired transistor characteristics. The measurements also demonstrate the possibility of realizing ambipolar transistors using InSb nanowires. For InSb nanowire quantum dots, both contact-induced Schottky-barrier-defined devices and top-finger-gate-defined devices are fabricated, and the Si substrate is used as a gate to tune the electron number in the quantum dots. The electrical measurements of these fabricated quantum-dot devices show the Coulomb-blockade effect at 4.2 K. A Fabry-Perot-like interference effect is also observed in a Schottky-barrier-defined quantum device. The authors also discuss in a comparative way, the results of measurements for the InSb nanowire devices made by different fabrication technologies employed in this study.
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| 41. |
- Nilsson, Henrik, et al.
(författare)
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Supercurrent and Multiple Andreev Reflections in an InSb Nanowire Josephson Junction
- 2012
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 12:1, s. 228-233
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxially grown, high quality semiconductor InSb nanowires are emerging material systems for the development of high performance nanoelectronics and quantum information processing and communication devices and for the studies of new physical phenomena in solid state systems. Here, we report on measurements of a superconductor-normal conductor-superconductor junction device fabricated from an InSb nanowire with aluminum-based superconducting contacts. The measurements show a proximity-induced supercurrent flowing through the InSb nanowire segment with a critical current tunable by a gate in the current bias configuration and multiple Andreev reflection characteristics in the voltage bias configuration. The temperature dependence and the magnetic field dependence of the critical current and the multiple Andreev reflection characteristics of the junction are also studied. Furthermore, we extract the excess current from the measurements and study its temperature and magnetic field dependences. The successful observation of the superconductivity in the InSb nanowire-based Josephson junction device indicates that InSb nanowires provide an excellent material system for creating and observing novel physical phenomena such as Majorana fermions in solid-state systems.
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| 42. |
- Nilsson, Henrik, et al.
(författare)
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Temperature dependent properties of InSb and InAs nanowire field-effect transistors
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:15
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Tidskriftsartikel (refereegranskat)abstract
- We present temperature dependent electrical measurements on InSb and InAs nanowire field-effect transistors (FETs). The FETs are fabricated from InAs/InSb heterostructure nanowires, where one complete transistor is defined within each of the two segments. Both the InSb and the InAs FETs are n-type with good current saturation and low voltage operation. The off-current for the InSb FET shows a strong temperature dependence, which we attribute to a barrier lowering due to an increased band-to-band tunneling in the drain part of the channel.
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| 43. |
- 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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| 44. |
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| 45. |
- Plissard, Sebastien, et al.
(författare)
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Gold-free growth of GaAs nanowires on silicon: arrays and polytypism
- 2010
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:38
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Tidskriftsartikel (refereegranskat)abstract
- We report growth by molecular beam epitaxy and structural characterization of gallium-nucleated GaAs nanowires on silicon. The influences of growth temperature and V/III ratio are investigated and compared in the case of oxide-covered and oxide-free substrates. We demonstrate a precise positioning process for Ga-nucleated GaAs nanowires using a hole array in a dielectric layer thermally grown on silicon. Crystal quality is analyzed by high resolution transmission electron microscopy. Crystal structure evolves from pure zinc blende to pure wurtzite along a single nanowire, with a transition region.
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| 46. |
- Roddaro, Stefano, et al.
(författare)
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Growth of vertical InAs nanowires on heterostructured substrates
- 2009
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:28
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the Au-assisted growth of InAs nanowires on two different kinds of heterostructured substrates: GaAs/AlGaAs structures capped by a 50 nm thick InAs layer grown by molecular beam epitaxy and a 2 mu m thick InAs buffer layer on Si(111) obtained by vapor phase epitaxy. Morphological and structural properties of substrates and nanowires are analyzed by atomic force and transmission electron microscopy. Our results indicate a promising direction for the integration of III-V nanostructures on Si-based electronics as well as for the development of novel micromechanical structures incorporating nanowires as their active elements.
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| 47. |
- Thelander, Claes, et al.
(författare)
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Development of a Vertical Wrap-Gated InAs FET
- 2008
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383. ; 55:11, s. 3030-3036
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report on the development of a vertical wrap-gated field-effect transistor based on epitaxially grown InAs nanowires. We discuss some of the important steps involved in the growth and processing, such as nanowire position control in situ doping, high-kappa dielectric deposition, spacer layer formation: and metal wrap-gate fabrication. In particular, we compare a few alternative methods for deposition of materials onto vertical structures and discuss their potential advantages and limitations. Finally, we also present a comparison of transistor performance for nanowires grown using two different epitaxial techniques.
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| 48. |
- Thelander, Claes, et al.
(författare)
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Effects of crystal phase mixing on the electrical properties of InAs nanowires
- 2011
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:April 29, 2011, s. 2424-2429
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic study of the relationship between crystal quality and electrical properties of InAs nanowires grown by MOVPE and MBE, with crystal structure varying from wurtzite to zinc blende. We find that mixtures of these phases can exhibit up to 2 orders of magnitude higher resistivity than single-phase nanowires, with a temperature-activated transport mechanism. However, it is also found that defects in the form of stacking faults and twin planes do not significantly affect the resistivity. These findings are important for nanowire-based devices, where uncontrolled formation of particular polytype mixtures may lead to unacceptable device variability.
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| 49. |
- Thelander, Claes, et al.
(författare)
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Electrical properties of InAs1-xSbx and InSb nanowires grown by molecular beam epitaxy
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:23
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Tidskriftsartikel (refereegranskat)abstract
- Results of electrical characterization of Au nucleated InAs1-xSbx nanowires grown by molecular beam epitaxy are reported. An almost doubling of the extracted field effect mobility compared to reference InAs nanowires is observed for a Sb content of x = 0.13. Pure InSb nanowires on the other hand show considerably lower, and strongly diameter dependent, mobility values. Finally, InAs of wurtzite crystal phase overgrown with an InAs1-xSbx shell is found to have a substantial positive shift in threshold voltage compared to reference nanowires. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726037]
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| 50. |
- Thelander, Claes, et al.
(författare)
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The electrical and structural properties of n-type InAs nanowires grown from metal-organic precursors.
- 2010
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:20
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Tidskriftsartikel (refereegranskat)abstract
- The electrical and structural properties of 111B-oriented InAs nanowires grown using metal-organic precursors have been studied. On the basis of electrical measurements it was found that the trends in carbon incorporation are similar to those observed in the layer growth, where an increased As/In precursor ratio and growth temperature result in a decrease in carbon-related impurities. Our results also show that the effect of non-intentional carbon doping is weaker in InAs nanowires compared to bulk, which may be explained by lower carbon incorporation in the nanowire core. We determine that differences in crystal quality, here quantified as the stacking fault density, are not the primary cause for variations in resistivity of the material studied. The effects of some n-dopant precursors (S, Se, Si, Sn) on InAs nanowire morphology, crystal structure and resistivity were also investigated. All precursors result in n-doped nanowires, but high precursor flows of Si and Sn also lead to enhanced radial overgrowth. Use of the Se precursor increases the stacking fault density in wurtzite nanowires, ultimately at high flows leading to a zinc blende crystal structure with strong overgrowth and very low resistivity.
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