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(a) Bright-field TEM image and an electron diffraction pattern from a single-crystal nanowire with a 100 nm scale bar, shown together with an X-ray diffractogram from a powder of sulfurized antimony selenide nanowires. (b) An EDX spectrum from a nanowire with composition Sb2Se1.35S1.65.
(Color online) (a) Representative current-voltage characteristics from an 80-nm-diameter nanowire at 250 K showing reversible resistance behavior. Switching from the linear Ohmic behavior to NDR behavior occurs at a threshold voltage VT. Inset shows an example nanowire device contacted with Au electrodes. (b) The current-voltage characteristics of an 80-nm-diameter nanowire at different temperatures in the 150-310 K temperature range in 10−7 Torr vacuum (colored solid curves) and a curve from the same device measured in air at 310 K (dotted line).
(Color online) (a) Semi-log plot of the threshold voltage VT as a function of reciprocal temperature exhibiting Arrhenius behavior. (b) Current-voltage curves from sub-100-nm diameter nanowires compared with >150 nm diameter nanowires in a 10−7 Torr vacuum (solid lines) and air (dotted lines); the nanowire diameter d is indicated. Inset is an extended current-voltage curve for a nanowire with d = 230 nm showing no threshold switching even at very high voltages.
(Color online) Schematic band diagrams for (a) V < VT and (b) V ≥ VT, where EC, ES, ED, and EF refer to the conduction band-edge, shallow states, deep traps, and the quasi-Fermi level, respectively. The Ohmic behavior with high σ at V < VT is due to thermally activated depopulation of ES levels. (b) For V ≥ VT, the ∼MV/cm fields induce impact ionization of the ED states, resulting in a sudden population inversion. Since the defect states are associated with the nanowire surface, the increase in free carrier concentration gives rise to a high conductivity surface shell, resulting in a voltage drop that causes NDR.
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