ZnO thin films have been grown heteroepitaxially on epi-GaN/sapphire (0001) substrates. Rutherford backscattering spectroscopy, ion channeling, and high resolution transmission electron microscopy studies revealed high-quality epitaxial growth of ZnO on GaN with an atomically sharp interface. The x-ray diffraction and ion channeling measurements indicate near perfect alignment of the ZnO epilayers on GaN as compared to those grown directly on sapphire (0001). Low-temperature cathodoluminescence studies also indicate high optical quality of these films presumably due to the close lattice match and stacking order between ZnO and GaN. Lattice-matched epitaxy and good luminescence properties of ZnO/GaN heterostructures are thus promising for ultraviolet lasers. These heterostructures demonstrate the feasibility of integrating hybrid ZnO/GaN optoelectronic devices.

Large-scale wurtzite GaN nanowires and nanotubes were grown by direct reaction of metal gallium vapor with flowing ammonia in an 850–900 °C horizontal oven. The cylindrical structures were as long as 500 μm with diameters between 26 and ∼100 nm. Transmission electron microscopy, scanning electron microscopy, and x-ray diffraction were used to measure the size and structures of the samples. Preliminary results show that the size of the nanowires depends on the temperature and the NH3 flow rate. The growth mechanism is discussed briefly. The simple method presented here demonstrates that GaN nanowires can be grown without the use of a template or catalyst, as reported elsewhere.

The authors report transport property measurements of individual GaN nanowire field effect transistors and the correlation of the electron mobilities with the existence of grain boundaries in these nanowires. Room temperature field effect electron mobilities as high as 319cm2V−1s−1 were obtained for the 200nm diameter nanowires. Mobilities calculated from these reliable nanowire field effect transistors indicated that the surface scattering plays a dominant role in smaller diameter nanowires, whereas for intermediate diameter devices transport is dominated by grain boundary scattering. Reduction of the mobility with decreasing diameter of nanowires can be explained using “continuous surface” model.

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We have utilized dielectrophoretic force for assembling long ͑50 m to 200 m͒ GaN nanowires for device fabrication. These catalyst-free nanowires were grown by direct reaction of NH 3 and Ga, which resulted in free-standing nanowires along with GaN microplatelets. GaN nanowires were suspended in a solvent using sonication, and using dielectrophoretic forces nanowires were assembled on prepatterned substrates ͑SiO 2 coated Si and sapphire͒. With fabrication sequence using batch fabrication processes such as standard photolithography, etching, and oxide deposition we were able to realize stable GaN nanowire devices. The present technique is potentially compatible with complementary metal-oxide semicondoctor technology, and integrating nanodevices with conventional Si microelectronics on the same chip can be made possible with this technique. Utilizing this technique, high mobility ͑230 cm 2 V −1 s −1 ͒ GaN nanowire field effect transistors with reliable electrical characteristics have been achieved. These nanowire transistors even after prolonged period of conduction exhibited no deteriorations of their electrical properties. Several key factors in the processing that affect the device yield and reliability have been identified. Simple calculations predicted the effects of nanowire geometry, dispersing solvent, and alignment frequency on the dielectrophoretic force experienced by the nanowires.