| 1. |
- Islam, Shadli, et al.
(författare)
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Ab-initio Calculation of Nonlinear Optical Susceptibilities in Germanium Quantum Dots
- 2019
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Ingår i: 2018 IEEE 13TH NANOTECHNOLOGY MATERIALS AND DEVICES CONFERENCE (NMDC). - 2378-377X. - 9781538610169 ; , s. 113-116
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Konferensbidrag (refereegranskat)abstract
- Using Time Independent Density Functional Theory (TIDFT) implemented in SIESTA (R) we calculated the 2nd order and 3rd order nonlinear optical susceptibilities of small Germanium Quantum Dots (GeQD). We observe that the symmetry breaking due to surface termination enhances chi((2)) up to 299.1 pm/V which promises a strong Second Harmonic Generation (SHG) in GeQDs. Diagonal components for chi((2)) tensor are 52.5, 11.2, 299.1 pm/V, for xxx, yyy and zzz, respectively. The 3rd order susceptibility, chi((3)), is within the range of (0.2-0.4) x 10(-18) m(2)/V-2 which is close to the reported experimental values of bulk Germanium. This study suggests possibilities of enhancing SHG in GeQDs through symmetry breaking via strain and surface termination/reconstruction as well as suitability of this fast and less-computationally intensive Density Functional Theory (DFT)-based method in predicting nonlinear optical susceptibilities of nano structures.
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| 2. |
- Shiri, Daryoush, 1975, et al.
(författare)
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Gunn-Hilsum Effect in Mechanically Strained Silicon Nanowires: Tunable Negative Differential Resistance
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Gunn (or Gunn-Hilsum) Effect and its associated negative differential resistivity (NDR) emanates from transfer of electrons between two different energy subbands. This effect was observed in semiconductors like GaAs which has a direct bandgap of very low effective mass and an indirect subband of high effective mass which lies ~300 meV above the former. In contrast to GaAs, bulk silicon has a very high energy spacing (~1 eV) which renders the initiation of transfer-induced NDR unobservable. Using Density Functional Theory (DFT), semi-empirical 10 orbital (sp 3 d 5 s ∗ ) Tight Binding and Ensemble Monte Carlo (EMC) methods we show for the first time that (a) Gunn Effect can be induced in silicon nanowires (SiNW) with diameters of 3.1 nm under +3% strain and an electric field of 5000 V/cm, (b) the onset of NDR in the I-V characteristics is reversibly adjustable by strain and (c) strain modulates the resistivity by a factor 2.3 for SiNWs of normal I-V characteristics i.e. those without NDR. These observations are promising for applications of SiNWs in electromechanical sensors and adjustable microwave oscillators. It is noteworthy that the observed NDC is different in principle from Esaki-Diode and Resonant Tunneling Diodes (RTD) in which NDR originates from tunneling effect.
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| 3. |
- Verma, Amit, et al.
(författare)
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Low-Temperature Effects on Electron Transport in Small-Diameter Silicon Nanowire
- 2023
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Ingår i: 2023 IEEE Nanotechnology Materials and Devices Conference (NMDC). - 9798350335460 ; , s. 31-34
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Konferensbidrag (refereegranskat)abstract
- We report on modeling studies on the effect of very low temperatures (4K-77K) on the behavior of electron transport in a [110] axially aligned, 1.3 nm diameter unstrained silicon nanowire (SiNW). A sp3d5s * tight-binding scheme is used to calculate the band structure within an Ensemble Monte Carlo simulation. Electron scattering occurs through bulk-acoustic and bulk-optical phonons and includes intra-subband and inter-subband events. A comparison with room temperature (300K) shows that at lower temperatures, average electron steady-state drift velocity increases by 2 or more times at relatively moderate electric fields. Transient average electron velocity also shows a more pronounced streaming motion. This is attributed to an overall decrease in electron-phonon scattering rates with temperature.
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