An asymmetric artificial scatterer in a semiconductor microjunction is shown to dramatically affect the nonlinear transport of ballistic electrons. The chosen device geometry, defined in a GaAs-AlGaAs heterostructure, successfully guides carriers in a predetermined spatial direction, independent of the direction of the input current $I$. From the nonlinear current-voltage characteristic we obtain unusual symmetry relations for the four-terminal resistances with $R_{ij,kl}\left(I\right)\approx {-R}_{ij,kl}(-I)$ and $R_{ij,kl}\left(B\right)\gg R_{kl,ij}(-B)$ even at zero magnetic field $B$. The ballistic rectifier thus realized relies on a new kind of rectification mechanism entirely different from that of an ordinary diode.

By tailoring the boundary of a narrow semiconductor channel to break its symmetry, we have realized a type of nanometer-scale nonlinear device, which we refer to as self-switching device (SSD). An applied voltage $V$ not only changes the potential profile along the channel direction, but also either widens or narrows the effective channel depending on the sign of $\mathrm{V.}$ This results in a diode-like characteristic but without the use of any doping junction or barrier structure. The turn-on voltage can also be widely tuned from virtually zero to more than 10 V, by simply adjusting the channel width. The planar and two-terminal structure of the SSD also allows SSD-based circuits to be realized by only one step of lithography.

Mechanically flexible mobile phones have been long anticipated due to the rapid development of thin-film electronics in the last couple of decades. However, to date, no such phone has been developed, largely due to a lack of flexible electronic components that are fast enough for the required wireless communications, in particular the speed-demanding front-end rectifiers. Here Schottky diodes based on amorphous indium–gallium–zinc–oxide (IGZO) are fabricated on flexible plastic substrates. Using suitable radio-frequency mesa structures, a range of IGZO thicknesses and diode sizes have been studied. The results have revealed an unexpected dependence of the diode speed on the IGZO thickness. The findings enable the best optimized flexible diodes to reach 6.3 GHz at zero bias, which is beyond the critical benchmark speed of 2.45 GHz to satisfy the principal frequency bands of smart phones such as those for cellular communication, Bluetooth, Wi-Fi and global satellite positioning.

A graphene ballistic rectifier is used in conjunction with an antenna to demonstrate a rectenna as a terahertz (THz) detector. A small-area (<1 μm²) local gate is used to adjust the Fermi level in the device to optimize the output while minimizing the impact on the cutoff frequency. The device operates in both n- and p-type transport regimes and shows a peak extrinsic responsivity of 764 V/W and a corresponding noise equivalent power of 34 pW Hz^–1/2 at room temperature with no indications of a cutoff frequency up to 0.45 THz. The device also demonstrates a linear response for more than 3 orders of magnitude of input power due to its zero threshold voltage, quadratic current–voltage characteristics and high saturation current. Finally, the device is used to take an image of an optically opaque object at 0.685 THz, demonstrating potential in both medical and security imaging applications.

We demonstrate that nanotubular networks formed by enzyme-triggered self-assembly of Fmoc-L₃ (9-fluorenylmethoxycarbonyl-tri-leucine) show significant charge transport. FT-IR, fluorescence spectroscopy and wide angle X-ray scattering (WAXS) data confirm formation of β-sheets that are locked together via π-stacking interactions. Molecular dynamics simulations confirmed the π–π stacking distance between fluorenyl groups to be 3.6–3.8 Å. Impedance spectroscopy demonstrated that the nanotubular xerogel networks possess minimum sheet resistances of 0.1 MΩ/sq in air and 500 MΩ/sq in vacuum (pressure: 1.03 mbar) at room temperature, with the conductivity scaling linearly with the mass of peptide in the network. These materials may provide a platform to interface biological components with electronics.

A high-performance solar-blind photodetector based on Cr-doped gallium oxide (Ga ₂ O ₃ ) has been fabricated. A 140-nm-thick Ga ₂ O ₃ layer was mechanically exfoliated from bulk crystal. The photodetector was based on a field-effect transistor structure, which showed a very high photo-to-dark current ratio larger than 10 ⁶ and excellent current saturation. When the photodetector was tested with a 254-nm ultra-violet light, the ratio of drain current with and without the UV light reached nearly six orders of magnitude. The dark current was as low as 5 pA. Furthermore, the current rise time and decay time were both about 25 ms. High responsivity of ${4.79} \times {10}^{{5}}$ A/W and external quantum efficiency of ${2.34} \times {10}^{{6}}$ also have been achieved at the same time.