Nanoscale emitters of terahertz radiation would be useful for a variety of applications, including investigations into the physical properties of nanostructured materials. Denis Seletskiy and co-workers of the University of New Mexico, Sandia National Laboratories and Air Force Research Laboratory in the USA have now shown that InAs nanowires may be suitable nanoscale sources of terahertz radiation. The researchers first prepared gold nanoparticles as InAs growth precursors on the GaAs substrate surface and then used metal–organic vapour phase epitaxy to fabricate InAs nanowires perpendicular to the substrate. The nanowires were 10–20 μm tall and had diameters that tapered from 450 nm at the base to 60 nm at the tip. Terahertz wave generation was achieved by illuminating the nanowires at an incident angle of 45° with 820 nm, 60 fs pulses from a Ti:sapphire laser. The researchers measured spectra of up to 5 THz through a linear autocorrelation technique. Taking into account the fact that the filling factor of the nanowires was only around 0.03, the radiation power was about 15 times larger than that of a bare planar InAs substrate. The researchers suggest that the presence of a low-energy acoustic surface plasmon mode was responsible for terahertz emission.
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