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Semiconductor nanowires (NWs) have shown evidence of robust hot carrier effects due to their small dimensions. The relaxation dynamics of hot carriers in these nanostructures, generated by photo-absorption, are of great importance in optoelectronic devices and high efficiency solar cells, such as hot carrier solar cells. Among various III-V semiconductors, indium arsenide (InAs) NWs are promising candidates for their applications in advanced light harvesting devices due to their high photo-absorptivity and high mobility. Here, we investigate the hot carrier dynamics in InAs-AlAsSb core-shell NWs, as well as bare-core InAs NWs, using ultrafast pump-probe spectroscopy with widely tuned pump and probe energies. We have found a lifetime of 2.3 ps for longitudinal optical (LO) phonons and hot electron lifetimes of about 3 ps and 30 ps for carrier-carrier interactions and electron-phonon interactions, respectively. In addition, we have investigated the electronic states in the AlAsSb-shell and found that, despite the large band offset of the core-shell design in the conduction band, excited carriers remain in the shell longer than 100 ps. Our results indicate evidence of plasmon-tailored core-shell NWs for efficient light harvesting devices, which could open potential avenues for improving the efficiency of photovoltaic solar cells.

Ultrathin InAs nanowires (NW) with one-dimensional (1D) sub-band structure are promising materials for advanced quantum-electronic devices, where dimensions in the sub-30 nm diameter limit together with post-CMOS integration scenarios on Si are much desired. Here, we demonstrate two site-selective synthesis methods that achieve epitaxial, high aspect ratio InAs NWs on Si with ultrathin diameters below 20 nm. The first approach exploits direct vapor-solid growth to tune the NW diameter by interwire spacing, mask opening size and growth time. The second scheme explores a unique reverse-reaction growth by which the sidewalls of InAs NWs are thermally decomposed under controlled arsenic flux and annealing time. Interesting kinetically limited dependencies between interwire spacing and thinning dynamics are found, yielding diameters as low as 12 nm for sparse NW arrays. We clearly verify the 1D sub-band structure in ultrathin NWs by pronounced conductance steps in low-temperature transport measurements using back-gated NW-field effect transistors. Correlated simulations reveal single- and double degenerate conductance steps, which highlight the rotational hexagonal symmetry and reproduce the experimental traces in the diffusive 1D transport limit. Modelling under the realistic back-gate configuration further evidences regimes that lead to asymmetric carrier distribution and lifts of the degeneracy in dependence of gate bias.

Organic semiconductors are usually not thought to show outstanding performance in highly-integrated, sub 100 nm transistors. Consequently, single-crystalline materials such as SWCNTs, MoS2 or inorganic semiconductors are the material of choice at these nanoscopic dimensions. Here, we show that using a novel vertical field-effect transistor design with a channel length of only 40 nm and a footprint of 2 x 80 x 80 nm$^2$, high electrical performance with organic polymers can be realized when using electrolyte gating. Our organic transistors combine high on-state current densities of above 3 MA/cm$^2$, on/off current modulation ratios of up to 108 and large transconductances of up to 5000 S/m. Given the high on-state currents at yet large on/off ratios, our novel structures also show promise for use in artificial neural networks, where they could operate as memristive devices with sub 100 fJ energy usage.