| 1. |
- 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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| 2. |
- Shekarforoush, Sima, et al.
(författare)
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Enhanced nonlinear optical susceptibilities in phosphorene nanoribbons: Ab initio study
- 2018
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:24
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Tidskriftsartikel (refereegranskat)abstract
- Using density functional theory method, the linear optical absorption spectra and nonlinear optical susceptibilities of hydrogen passivated armchair and zigzag Phosphorous Nanoribbons (aPNR and zPNR) as well as α-phase phosphorous monolayer were calculated. It was observed that the crystallographic direction has a strong effect on the band edge absorption which in turn leads to optical anisotropy as well as a red shift of the absorption spectra by increasing the width. The calculated absorption values are in the order of 105cm-1and are very close to the experimentally measured ones. It was also observed that the 2nd order nonlinear optical susceptibility, χ(2), in the nanoribbons is enhanced by two orders of magnitude. This effect is caused by breaking the centro-symmetric structure of monolayer phosphorene as a result of hydrogen surface termination. The calculated 3rd order susceptibilities, χ(3), are in the order of ≈10-13esu (≈10-21m2/V2) which are in close agreement with experimentally reported values as well as those computed based on the relativistic picture of electron. The closeness of our results to experimental values strongly supports the reliability of our method in calculating the nonlinear optical susceptibilities of phosphorene and other nanostructures in general. The enhanced 2nd order optical nonlinearity in phosphorene promises a better second harmonic and frequency difference (THz) generation.
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| 3. |
- Shekarforoush, Sima, et al.
(författare)
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Optical transitions and localized edge states in skewed zigzag phosphorene nanoribbons
- 2018
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Ingår i: Materials Express. - : American Scientific Publishers. - 2158-5857 .- 2158-5849. ; 8:6, s. 489-499
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Tidskriftsartikel (refereegranskat)abstract
- Using the Tight Binding (TB) parameters extracted from Density Functional Theory (DFT) and Recursive Green's Function method (RGF), it is shown that skewed-zigzag black phosphorus (phosphorene) nanoribbons obtain large and tuneable bandgap in response to vertical and transverse electric fields. Depending on the direction of the applied field the mid-gap states could possess the localized or metallic nature i.e., non-zero midgap density of states. Adjustability of the bandgap and optical dipole transition matrix elements are explained based on the symmetry of involved band edge states. This promises new electronic and optical devices based on phosphorene nanoribbons.
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