High-speed metal-semiconductor-metal ͑MSM͒ photodetectors based on Schottky-contacted core/ shell GaAs/AlGaAs and bare GaAs nanowires were fabricated and characterized. The measured core/shell temporal response has a ϳ10 ps full-width at half-maximum and an estimated corrected value less than 5 ps. The bare GaAs devices exhibit a slower response ͑ϳ35 ps͒ along with a slow decaying persistent photocurrent ͑ϳ80 s͒. The core/shell devices exhibit significantly improved dc and high-speed performance over bare nanowires and comparable performance to planar MSM photodetectors. The picosecond temporal response, coupled with picoampere dark current, demonstrate the potential for core/shell nanowires in high-speed imaging arrays and on-chip optical interconnects.

Articles you may be interested inControlling the polarity of metalorganic vapor phase epitaxy-grown GaP on Si(111) for subsequent III-V nanowire growth Appl. Phys. Lett. 106, 231601 (2015); 10.1063/1.4922275GaAs whiskers grown by metal-organic vapor-phase epitaxy using Fe nanoparticles Au-catalyzed self-assembly of GaAs nanowires on ͑111͒B GaAs by metalorganic vapor phase epitaxy is reported between 375 and 500°C, using tertiarybutylarsine and trimethylgallium in H 2 . The nanowires are ͓111͔B aligned and kink-free. Below 425°C the nanowires have narrow base diameter distributions, closely matching the size ͑ϳ60 nm͒ of the Au nanoparticles at their tip ͑no tapering͒. Above 425°C the nanowires show a hexagonal-based pyramidal shape with base edges normal to the ͗211͘ in-plane substrate directions and base diameters which increase exponentially with temperature, indicating a kinetics limited growth along the nanowire sidewalls. Activation energies in the range of ϳ20-23 kcal/ mol were estimated for growth along both the sidewalls and the ͓111͔B direction.

Gold nanoparticles heavily functionalized with oligonucleotides have been used in a variety of DNA detection methods. The optical properties of three-dimensional aggregates of Au nanoparticles in solution or deposited onto suitable surfaces have been analyzed to detect hybridization processes of specific DNA sequences as possible alternatives to fluorescent labeling methods. This paper reports on the preparation of gold nanoparticles directly deposited onto the surface of silicon (Si) and sapphire (Al2O3) substrates by a physical methodology, consisting in the thermal evaporation of a thin Au film and its successive annealing. The method guarantees the preparation of monodispersed single-crystal Au nanoparticles with a strong surface plasmon resonance (SPR) peak centered at about 540 nm. We show that the changes of SPR excitation before and after DNA functionalization and subsequent hybridization of Au nanoparticles immobilized onto Si and Al2O3 substrates can be exploited to fabricate specific biosensors devices in solid phase.