Here we report InAs nanowire (NW) near-infrared photodetectors having a detection wavelength up to ∼1.5 μm. The single InAs NW photodetectors displayed minimum hysteresis with a high Ion/Ioff ratio of 10(5). At room temperature, the Schottky-Ohmic contacted photodetectors had an external photoresponsivity of ∼5.3 × 10(3) AW(-1), which is ∼300% larger than that of Ohmic-Ohmic contacted detectors (∼1.9 × 10(3) AW(-1)). A large enhancement in photoresponsivity (∼300%) had also been achieved in metal Au-cluster-decorated InAs NW photodetectors due to the formation of Schottky junctions at the InAs/Au cluster contacts. The photocurrent decreased when the photodetectors were exposed to ambient atmosphere because of the high surface electron concentration and rich surface defect states in InAs NWs. A theoretical model based on charge transfer and energy band change is proposed to explain this observed performance. To suppress the negative effects of surface defect states and atmospheric molecules, new InAs NW photodetectors with a half-wrapped top-gate had been fabricated by using 10 nm HfO2 as the top-gate dielectric.

Graphene is a promising candidate material for high-speed and ultra-broadband photodetectors. However, graphene-based photodetectors suffer from low photoreponsivity and I(light)/I(dark) ratios due to their negligible-gap nature and small optical absorption. Here, a new type of graphene/InAs nanowire (NW) vertically stacked heterojunction infrared photodetector is reported, with a large photoresponsivity of 0.5 AW(-1) and I(light)/I(dark) ratio of 5 × 10(2), while the photoresponsivity and I(light)/I(dark) ratio of graphene infrared photodetectors are 0.1 mAW(-1) and 1, respectively. The Fermi level (E(F)) of graphene can be widely tuned by the gate voltage owing to its 2D nature. As a result, the back-gated bias can modulate the Schottky barrier (SB) height at the interface between graphene and InAs NWs. Simulations further demonstrate the rectification behavior of graphene/InAs NW heterojunctions and the tunable SB controls charge transport across the vertically stacked heterostructure. The results address key challenges for graphene-based infrared detectors, and are promising for the development of graphene electronic and optoelectronic applications.

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The doping-dependent photoconductive properties of individual GaAs nanowires have been studied by conductive atomic force microscopy. Linear responsivity against the bias voltage is observed for moderate n-doped GaAs wires with a Schottky contact under illumination, while that of the undoped ones exhibits a saturated response. The carrier lifetime of a single nanowire can be obtained by simulating the characteristic photoelectric behavior. Consistent with the photoluminescence results, the significant drop of minority hole lifetime, from several hundred to subpicoseconds induced by n-type doping, leads to the distinct photoconductive features. Moreover, by comparing with the photoelectric behavior of AlGaAs shelled nanowires, the equivalent recombination rate of carriers at the surface is assessed to be >1 × 10(12) s(-1) for 2 × 10(17)cm(-3) n-doped bare nanowires, nearly 30 times higher than that of the doping-related bulk effects. This work suggests that intentional doping in nanowires could change the charge status of the surface states and impose significant impact on the electrical and photoelectrical performances of semiconductor nanostructures.

In this study, the structural quality of Au-catalyzed InAs nanowires grown by molecular beam epitaxy is investigated. Through detailed electron microscopy characterizations and analysis of binary Au-In phase diagram, it is found that defect-free InAs nanowires can be induced by smaller catalysts with a high In concentration, while comparatively larger catalysts containing less In induce defected InAs nanowires. This study indicates that the structural quality of InAs nanowires can be controlled by the size of Au catalysts when other growth conditions remain as constants.

In this study, we demonstrate the epitaxial growth of ⟨001̅⟩ defect-free zinc-blende structured InAs nanowires on GaAs {111}B substrate using Au catalysts in molecular beam epitaxy. It has been found that the catalysts and their underlying ⟨001̅⟩ nanowires have the orientation relationship of {11̅03}C//{002̅}InAs and [3̅302]C//[11̅0]InAs due to their small in-plane lattice mismatches between their corresponding lattice spacings perpendicular to the {001̅} atomic planes of the nanowires, leading to the formation of the {001̅} catalyst/nanowire interfaces, and consequently the formation of ⟨001̅⟩ nanowires. This study provides a practical approach to manipulate the crystal structure and structural quality of III-V nanowires through carefully controlling the crystal phase of the catalysts.

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