| 1. |
- Löfstrand, Anette, et al.
(författare)
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Feature size control using surface reconstruction temperature in block copolymer lithography for InAs nanowire growth
- 2020
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:32
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a method to control the size of the openings in hexagonally organized BCP thin films of poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) by using surface reconstruction. The surface reconstruction is based on selective swelling of the P4VP block in ethanol, and its extraction to the surface of the film, resulting in pores upon drying. We found that the BCP pore diameter increases with ethanol immersion temperature. In our case, the temperature range 18 to 60 °C allowed fine-Tuning of the pore size between 14 and 22 nm. A conclusion is that even though the molecular weight of the respective polymer blocks is fixed, the PS-b-P4VP pore diameter can be tuned by controlling temperature during surface reconstruction. These results can be used for BCP-based nanofabrication in general, and for vertical nanowire growth in particular, where high pattern density and diameter control are of importance. Finally, we demonstrate successful growth of indium arsenide InAs vertical nanowires by selective-Area metal-organic vapor phase epitaxy (MOVPE), using a silicon nitride mask patterned by the proposed PS-b-P4VP surface reconstruction lithography method.
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| 2. |
- Aberg, I, et al.
(författare)
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Nanoscale tungsten aerosol particles embedded in GaAs
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:16, s. 2976-2978
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Tidskriftsartikel (refereegranskat)abstract
- GaAs containing buried nanoscale tungsten particles has been characterized electrically. The particles were produced using a special aerosol process and were embedded in GaAs by epitaxial overgrowth. Two different particle sizes were investigated separately. When the particle concentration was increased, a conductance drop of about 500 times was observed. A simulation model, based on a random distribution of the particles, was developed and used to support our findings. The major advantage of our method is the simplicity and low processing cost.
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| 3. |
- Achermann, M, et al.
(författare)
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Carrier and field dynamics around nanoscale Schottky contacts investigated by ultrafast near-field optics
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 65:4
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Tidskriftsartikel (refereegranskat)abstract
- We present femtosecond-resolved optical near-field pump-probe measurements of spatiotemporal carrier dynamics around a single nanoscale tungsten (W) disk embedded in GaAs. In these samples, Schottky contacts are formed at the W/GaAs interface. The experimental results are modeled by a selfconsistent treatment of the drift-diffusion equation for the carriers and Poisson's equation for the built-in electric field. At lower optically excited carrier densities, we observe that the built-in field suppresses electron transport towards and trapping into the metal particles. In this regime, an accumulation of carriers is seen at the edge of the depletion region of the Schottky contacts. The calculation reveals that the formation of a self-induced dynamic potential well is the origin of this result. In the high-density regime, efficient carrier transport towards and trapping into the W nanoparticle take place, resulting from the screening of the built-in field. These results allow us to describe measurements of the carrier dynamics in annealed low-temperature grown GaAs and demonstrate that the coupling of the carrier and field dynamics can substantially affect carrier trapping in metal-semiconductor composite materials.
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| 4. |
- Achermann, M, et al.
(författare)
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Carrier dynamics around nano-scale Schottky contacts: a femtosecond near-field study
- 2002
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Ingår i: Applied Surface Science. - 1873-5584. ; 190:1-4, s. 513-516
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Tidskriftsartikel (refereegranskat)abstract
- We report spatially and time-resolved measurements of ultrafast carrier dynamics around buried nano-scale Schottky contacts, performed with a novel femtosecond near-field scanning optical microscope. The experimental results are modeled by a self-consistent treatment of the drift-diffusion equation for the carriers and Poisson's equation for the built-in electric field. We show that the built-in field suppresses electron transport towards and trapping into the metal particles at lower optically excited carrier densities. In contrast, efficient electron trapping into the metal occurs at higher electron densities, which screen the built-in field, allowing for efficient transport of electrons towards the Schottky contact. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 5. |
- Achermann, M, et al.
(författare)
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Nano-scale Schottky contacts: ultrafast drift-diffusion dynamics studied in the optical near field
- 2002
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 13:2-4, s. 819-822
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Tidskriftsartikel (refereegranskat)abstract
- We present direct measurements of the ultrafast carrier dynamics around buried nano-scale Schottky contacts with high spatial and time resolution, performed with a novel fermosecond near-field scanning optical microscope, It is shown that high optically excited carrier densities screen the built-in field around a Schottky contact and allow for efficient transport of electrons towards the contact, followed by trapping of electrons into the metal. The experimental results are modeled by a self-consistent treatment of the drift-diffusion equation for the carriers and Poisson's equation for the built-in electric field. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 6. |
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| 7. |
- 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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| 8. |
- Astromskas, Gvidas, et al.
(författare)
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Heterogeneous integration of InAs on W/GaAs by MOVPE
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 100, s. 042043-042043
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Konferensbidrag (refereegranskat)abstract
- InAs has been grown on W-GaAs patterned substrates using MOVPE. The selectivity of the growth and the nucleation process has been studied as a function of the temperature and the V/III-ratio in the MOVPE reactor. It is shown that the W guides the nucleation of the InAs on the GaAs and that the islands formed may be used to embed metal features in a hybride InAs/GaAs structure in agreement with previous overgrowth studies of W-InAs and W-GaAs. The electrical properties has also been evaluated demonstrating a reduction of resistance by a factor 5 for a hybride structure with an embedded grating as compared to an InAs/GaAs reference sample.
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| 9. |
- 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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| 10. |
- 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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