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High-quality one-dimensional GaN rods and nanowires were grown on Ni-coated c-plan sapphire substrate using halide vapor-phase epitaxy (HVPE). Their structure and optical properties were investigated by X-ray diffractometery, scanning and transmission electron microscopy, and photoluminescence techniques. A high density of straight and aligned one-dimensional GaN nanowires with a diameter of 80 nm was uniformly formed on the entire substrate at 700 • C. The X-ray diffraction patterns, transmission electron microscopic images, and selective area electron diffraction patterns indicate that the one-dimensional GaN are nanostructure pure single crystals preferentially oriented in the [001] direction. Photoluminescence analysis revealed that the HVPE grown GaN nanowires have high optical quality.

Single-crystalline AlN nanostructures, such as thin films, nanoneedles, nanocolumns, and nanowires, depending on the controlled gas-flow ratio, are synthesized by halide vapor-phase epitaxy (HVPE). In comparison with a typical vapor/ liquid/solid (VLS) mechanism for the growth of nanowires, well-aligned AlN nanorod arrays with diameters below 20 nm are grown on a catalyst-free Si substrate though a vapor/solid (VS) mechanism. Their structural and optical properties are measured by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL). In particular, AlN nanorods exhibit an excellent field emission property with a low turn-on field of 2.25 V mm À1. The field enhancement factor is estimated to be about 784 due to well-aligned, needle-shaped, AlN nanorods.

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