Semiconductor nanowires have become an important building block for nanotechnology. The growth of semiconductor nanowires using a metal catalyst via the vapor-liquid-solid (VLS) or vapor-solid-solid (VSS) mechanism has yielded growth directions in 1 1 1 , 1 0 0 and 1 1 0 etc. In this paper, we summarize and discuss a broad range of factors that affect the growth direction of VLS or VSS grown epitaxial semiconductor nanowires, providing an indexed glimpse of the control of nanowire growth directions and thus the mechanical, electrical and optical properties associated with the crystal orientation. The prospect of using planar nanowires for large area planar processing toward future nanowire array-based nanoelectronics and photonic applications is discussed.

We report the controlled growth of planar GaAs semiconductor nanowires on (100) GaAs substrates using atmospheric pressure metalorganic chemical vapor deposition with Au as catalyst. These nanowires with uniform diameters are self-aligned in <110> direction in the plane of (100). The dependence of planar nanowire morphology and growth rate as a function of growth temperature provides insights into the growth mechanism and identified an ideal growth window of 470 +/- 10 degrees C for the formation of such planar geometry. Transmission electron microscopy images reveal clear epitaxial relationship with the substrate along the nanowire axial direction, and the reduction of twinning defect density by about 3 orders of magnitude compared to <111> III-V semiconductor nanowires. In addition, using the concept of sacrificial layers and elevation of Au catalyst modulated by growth condition, we demonstrate for the first time a large area direct transfer process for nanowires formed by a bottom-up approach that can maintain both the position and alignment. The planar geometry and extremely low level of crystal imperfection along with the transferability could potentially lead to highly integrated III-V nanoelectronic and nanophotonic devices on silicon and flexible substrates.

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III-V compound semiconductor nanowires (NWs), with their direct bandgaps and high mobilities, have been shown to be promising materials for many applications including solar cells, light emitting diodes, transistors, and lasers. Self-aligned, twin-plane-defect free, planar GaAs NWs can be grown by metalorganic chemical vapor deposition (MOCVD) through the Au-assisted vapor-liquid-solid mechanism. In this report, <110> planar GaAs NW growth on GaAs (100) substrates is perturbed by introducing common p-type dopant impurities, zinc (Zn) or carbon (C), and characterized structurally and electrically. The implications of the results on planar NW growth and doping mechanism are discussed.

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Optical antennas can enhance the spontaneous emission rate from nanoemitters by orders of magnitude, enabling the possibility of an ultrafast, efficient, nanoscale LED. Semiconductors would be the preferred material for such a device to allow for direct high-speed modulation. However, efficient nanoscale devices are challenging to implement because of high surface recombination typical of most III−V materials. Monolayer transition metal dichalcogenides are an attractive alternative to a III−V emitter due to their intrinsically nanoscale dimensions, direct bandgap, and nearideal surfaces resulting in high intrinsic quantum yield. In this work, we couple a nanostrip (30 nm × 250 nm) monolayer of WSe 2 to a cavity-backed optical slot antenna through a self-aligned fabrication process. Photoluminescence, scattering, and lifetime measurements are used to estimate a radiative spontaneous emission rate enhancement of 318× from WSe 2 monolayers coupled to on-resonance antennas. Such a huge increase in the spontaneous emission rate results in an ultrafast radiative recombination rate and a quantum yield in nanopatterned monolayers comparable to unprocessed exfoliated flakes of WSe 2 .

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