We report on experiments, and their analysis, on electron heating effects in 3.2 pm long free-standing fine wires (triangular cross-section with ~0 . 5 pm side) of single-crystal GaAs doped at 10" ~m -~.The data can be used to extract a thermal conductivity that has a linear temperature dependence, consistent with a contribution from electrons and/or onedimensional phonons. We show that the electronic contribution dominates.
The efficient modulation and control of ultrafast signals on-chip is of central importance in terahertz (THz) communications and a promising route toward sub-diffraction limit THz spectroscopy. Two-dimensional (2D) materials may provide a platform for these endeavors. We explore this potential, integrating high-quality graphene p-n junctions within two types of planar transmission line circuits to modulate and emit picosecond pulses. In a coplanar stripline geometry, we demonstrate electrical modulation of THz signal transmission by 95%. In a Goubau waveguide geometry, we achieve complete gate-tunable control over THz emission from a photoexcited graphene junction. These studies inform the development of on-chip signal manipulation and highlight prospects for 2D materials in THz applications.
We extend our previous studies of the heating by DC electric fields of submicron-diameter free-standing wires of doped GaAs at low lattice temperatures. For lower fields, equivalent to sub-nanowatt dissipated power in our samples, all thermal processes could be accounted for in terms of electron heating alone. We consider here the regime where the hot electrons deposit some of their excess energy into the host lattice, we extract a characteristic electronphonon scattering length that is an appreciable fraction of the sample length, and we provide evidence for ballistic phonon transport
A fabrication process for free-standing single-crystal silicon wires of submicrometer cross-sectional dimensions and lengths in excess of 40 μm is reported. The starting material is silicon-on-insulator that has been recrystallized using a dual electron beam recrystallizing system. The wires are then fabrictaed in the recrystallized layer by a combination of electron beam lithography and plasma etching. Electrical measurements have been performed and the fabrication limits of the process are discussed.
Low-temperature electrical and magnetoresistance measurements have been performed on free-standing and supported wires of n-type GaAs doped to 10" ~1 1 7 ~~ over the temperature range 0.47-4.2 K. These wires were triangular in cross-section, with widths of 600-900 nm and lengths of 3.2-10 pm. We report that the observedincrease in the resistance for temperatures below 4.2 K can be interpreted as being due to a combination of weak localisation of 3D electron-electron interaction effects. We will also show how the results described here can be used as the basis for a determination of the phonon conductivity and dimensionality in free-standing structures.
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