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(a) High-angle annular dark field image of InAs- core-shell nanowire with superimposed energy-dispersive x-ray spectroscopy linescan (Al: red, In: blue, As: green). (b) High-resolution TEM image taken along the zone axis, showing an absence of dislocations in the shell. The dashed line indicates the nanowire surface. (c) Schematic cross-section of the FET device. (d) SEM image of device 3. The etching profile of the nanowire is seen near the metal contact at the upper left.
(a) Conductance versus backgate voltage for core-shell nanowire FET device 1, at various temperatures. (b) Pinchoff threshold voltage as a function of temperature for device 1. (c) Field-effect (red dots) and effective (black squares) mobility versus backgate voltage for device 1 at T = 14 K. The effective mobility remains a smooth function despite the oscillations in conductance that appear at low temperatures. The peak effective mobilities are used in subsequent analysis.
Peak effective electron mobility versus temperature for core-shell devices 1–3 (upper panel) and unpassivated devices 4–6 (lower panel). The estimated nanowire diameters (core diameters for devices 1–3) are indicated in the legend in parentheses. Empirical fits are based on a single power law for the core-shell devices, and a two-component form for the unpassivated devices, where are fitting parameters. On average, mobility increases with nanowire diameter, as is seen here for the unpassivated nanowires.
Carrier electron concentrations at peak mobility, versus temperature, for core-shell devices (upper panel) and unpassivated devices (lower panel). The estimated nanowire diameters are indicated in the legend. The solid lines in the upper plot are empirical fits of the form , where n is concentration, T is temperature, and A and B are fitting parameters. The slopes B obtained are , and for devices 1, 2, and 3, respectively. The concentrations for the unpassivated nanowires show more scatter, but are largely independent of temperature below 100 K.
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