| 1. |
- Gluschke, J.G., et al.
(författare)
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Using Ultrathin Parylene Films as an Organic Gate Insulator in Nanowire Field-Effect Transistors
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:7, s. 4431-4439
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Tidskriftsartikel (refereegranskat)abstract
- We report the development of nanowire field-effect transistors featuring an ultrathin parylene film as a polymer gate insulator. The room temperature, gas-phase deposition of parylene is an attractive alternative to oxide insulators prepared at high temperatures using atomic layer deposition. We discuss our custom-built parylene deposition system, which is designed for reliable and controlled deposition of <100 nm thick parylene films on III–V nanowires standing vertically on a growth substrate or horizontally on a device substrate. The former case gives conformally coated nanowires, which we used to produce functional Ω-gate and gate-all-around structures. These give subthreshold swings as low as 140 mV/dec and on/off ratios exceeding 103 at room temperature. For the gate-all-around structure, we developed a novel fabrication strategy that overcomes some of the limitations with previous lateral wrap-gate nanowire transistors. Finally, we show that parylene can be deposited over chemically treated nanowire surfaces, a feature generally not possible with oxides produced by atomic layer deposition due to the surface “self-cleaning” effect. Our results highlight the potential for parylene as an alternative ultrathin insulator in nanoscale electronic devices more broadly, with potential applications extending into nanobioelectronics due to parylene’s well-established biocompatible properties.
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| 2. |
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| 3. |
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| 4. |
- Burke, Adam, et al.
(författare)
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InAs Nanowire Transistors with Multiple, Independent Wrap-Gate Segments.
- 2015
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:5, s. 2836-2843
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Tidskriftsartikel (refereegranskat)abstract
- We report a method for making horizontal wrap-gate nanowire transistors with up to four independently controllable wrap-gated segments. While the step up to two independent wrap-gates requires a major change in fabrication methodology, a key advantage to this new approach, and the horizontal orientation more generally, is that achieving more than two wrap-gate segments then requires no extra fabrication steps. This is in contrast to the vertical orientation, where a significant subset of the fabrication steps needs to be repeated for each additional gate. We show that cross-talk between adjacent wrap-gate segments is negligible despite separations less than 200 nm. We also demonstrate the ability to make multiple wrap-gate transistors on a single nanowire using the exact same process. The excellent scalability potential of horizontal wrap-gate nanowire transistors makes them highly favorable for the development of advanced nanowire devices and possible integration with vertical wrap-gate nanowire transistors in 3D nanowire network architectures.
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| 5. |
- Carrad, Damon J., et al.
(författare)
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Electron-Beam Patterning of Polymer Electrolyte Films To Make Multiple Nanoscale Gates for Nanowire Transistors
- 2014
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:1, s. 94-100
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Tidskriftsartikel (refereegranskat)abstract
- We report an electron-beam based method for the nanoscale patterning of the poly(ethylene oxide)/LiClO4 polymer electrolyte. We use the patterned polymer electrolyte as a high capacitance gate dielectric in single nanowire transistors and obtain subthreshold swings comparable to conventional metal/oxide wrap-gated nanowire transistors. Patterning eliminates gate/contact overlap, which reduces parasitic effects and enables multiple, independently controllable gates. The method's simplicity broadens the scope for using polymer electrolyte gating in studies of nanowires and other nanoscale devices.
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| 6. |
- Jacobsson, Daniel, et al.
(författare)
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Particle-assisted GaxIn1-xP nanowire growth for designed bandgap structures
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:24
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Tidskriftsartikel (refereegranskat)abstract
- Non-tapered vertically straight GaxIn1-xP nanowires were grown in a compositional range from Ga0.2In0.8P to pure GaP in particle-assisted mode by controlling the trimethylindium, trimethylgallium and hydrogen chloride flows in metal-organic vapor phase epitaxy. X-ray energy dispersive spectroscopy in transmission electron microscopy revealed homogeneous radial material composition in single nanowires, whereas variations in the material composition were found along the nanowires. High-resolution x-ray diffraction indicates a variation of the material composition on the order of about 19% measuring an entire sample area, i.e., including edge effects during growth. The non-capped nanowires emit room temperature photoluminescence strongly in the energy range of 1.43-2.16 eV, correlated with the bandgap expected from the material composition.
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| 7. |
- Nemec, H., et al.
(författare)
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Bulk-like transversal electron mobility in heavily n-doped InP nanowires probed by terahertz spectroscopy
- 2014
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Ingår i: 2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2014. - 9781479938773
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Konferensbidrag (refereegranskat)abstract
- Waveguiding of excitation beam and propagation of THz beam in a complex gradient environment were studied in an array of InP nanowires. Measurements by time-resolved THz spectroscopy accompanied by Monte-Carlo calculations of the response of localized charges enabled determination of transversal electron mobility.
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| 8. |
- Vasen, T., et al.
(författare)
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InAs nanowire GAA n-MOSFETs with 12-15 nm diameter
- 2016
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Ingår i: 2016 IEEE Symposium on VLSI Technology, VLSI Technology 2016. - 9781509006373 ; 2016-September
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Konferensbidrag (refereegranskat)abstract
- InAs nanowires (NW) grown by MOCVD with diameter d as small as 10 nm and gate-All-Around (GAA) MOSFETs with d = 12-15 nm are demonstrated. Ion = 314 μA/μm, and Ssat =68 mV/dec was achieved at Vdd = 0.5 V (Ioff = 0.1 μA/μm). Highest gm measured is 2693 μS/μm. Device performance is enabled by small diameter and optimized high-k/InAs gate stack process. Device performance tradeoffs between gm, Ron, and Imin are discussed.
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| 9. |
- Aghaeipour, Mahtab
(författare)
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Tailoring the Optical Response of III-V Nanowire Arrays
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Semiconductor nanowires show a great deal of promise for applications in a wide range of important fields, including photovoltaics, biomedicine, and information technology. Developing these exciting applications is strongly dependent on understanding the fundamental properties of nanowires, such as their optical resonances and absorption spectra. In this thesis we explore optical absorption spectra of arrays of vertical III-V nanowires with a special emphasis on structures optimized to enhance absorption in the solar spectrum. First, we analyze experimentally determined absorption spectra of both indium phosphide (InP) and gallium phosphide (GaP) nanowire arrays. The study provides an intuitive understanding of how the observed absorption resonances in the nanowires may be tuned as a function of their geometrical parameters and crystal structure. As a consequence, the spectral position of absorption resonances can be precisely controlled through the nanowire diameter. However, the results highlight how the blue-shift in the optical absorption resonances as the diameter of the nanowires decreases comes to a halt at low diameters. The stop point is related to the behavior of the refractive indices of the nanowires. The wavelength of the stop is different for nanowire polytypes of similar dimensions due to differences in their refractive indices. We then present a theoretical argument that it is important to consider symmetry properties when tailoring the optical modes excited in the nanowires for enhanced absorption. We show that absorption spectra may be enhanced compared to vertical nanowires at normal incidence by tilting the nanowires with normal incidence light, or by using off-normal incidence with vertical nanowires. This is because additional optical modes inside the nanowires are excited when the symmetry is broken. Looking forward to omnidirectional applications, we consider branched nanowires as a way to enhance the absorption spectra at normal incidence by taking advantage of simultaneous excitation of the spectrally different optical modes in the branches and the stems. Third, we describe in theoretical terms how integrating distributed Bragg reflectors (DBRs) with the nanowires can improve absorption spectra compared to conventional nanowires. DBRs provide a way to employ light trapping mechanisms which increases the optical path length of the excited modes and thereby improves the absorption of the excited modes. At normal incidence, DBR-nanowires improve the absorption efficiency to 78%, compared to 72% for conventional nanowires. We show that the efficiency is increased to 85% for an off-normal incident angle of 50˚. Overall, our results show that studies of optical resonances in nanowires that take the light-matter interaction into account provide opportunities to develop novel optical and optoelectronic functionalities in nanoscience and nanotechnology.
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| 10. |
- Ba, Alexandre, et al.
(författare)
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Inter-laboratory comparison of channelized hotelling observer computation
- 2018
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Ingår i: Medical Physics. - : Wiley. - 0094-2405 .- 2473-4209. ; 45:7, s. 3019-3030
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The task-based assessment of image quality using model observers is increasingly used for the assessment of different imaging modalities. However, the performance computation of model observers needs standardization as well as a well-established trust in its implementation methodology and uncertainty estimation. The purpose of this work was to determine the degree of equivalence of the channelized Hotelling observer performance and uncertainty estimation using an intercomparison exercise. Materials and Methods: Image samples to estimate model observer performance for detection tasks were generated from two-dimensional CT image slices of a uniform water phantom. A common set of images was sent to participating laboratories to perform and document the following tasks: (a) estimate the detectability index of a well-defined CHO and its uncertainty in three conditions involving different sized targets all at the same dose, and (b) apply this CHO to an image set where ground truth was unknown to participants (lower image dose). In addition, and on an optional basis, we asked the participating laboratories to (c) estimate the performance of real human observers from a psychophysical experiment of their choice. Each of the 13 participating laboratories was confidentially assigned a participant number and image sets could be downloaded through a secure server. Results were distributed with each participant recognizable by its number and then each laboratory was able to modify their results with justification as model observer calculation are not yet a routine and potentially error prone. Results: Detectability index increased with signal size for all participants and was very consistent for 6 mm sized target while showing higher variability for 8 and 10 mm sized target. There was one order of magnitude between the lowest and the largest uncertainty estimation. Conclusions: This intercomparison helped define the state of the art of model observer performance computation and with thirteen participants, reflects openness and trust within the medical imaging community. The performance of a CHO with explicitly defined channels and a relatively large number of test images was consistently estimated by all participants. In contrast, the paper demonstrates that there is no agreement on estimating the variance of detectability in the training and testing setting.
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