Although light emission from a single nanorod has been reported, this article reports the light emission from nanorod vertical array and their electroluminescence spectra. It demonstrates the bright electroluminescent devices based on 1D semiconducting nanostructure arrays. In particular, simple heteroepitaxial growth of n-type ZnO nanorods on p-type GaN resulted in the formation of nanosized junction, yielding high current density along with bright electroluminescence. We believe that this simple "bottom-up" heteroepitaxial approach might readily be expanded to fabricate many other electronic and photonic devices based on many other heteroepitaxial semiconductor nanostructures.

Vertically aligned ZnO nanorod heteroepitaxial growth by catalyst-free metal-organic vapor phase epitaxy creates opportunities for the fabrication of photonic and electronic nanodevice arrays. Simple heteroepitaxial growth yields vertically aligned ZnO nanorods on GaN substrates, resulting in the formation of nanosized junctions. The p-n heterojunction nanorod electroluminescent devices showed strong electroluminescence. More generally, we believe that the simple "bottom up" heteroepitaxial approach might readily be expanded to fabricate many other heteroepitaxial semiconductor nanorod EL devices and arrays. We used heterojunction of n-ZnO nanorod arrays vertically grown on p-GaN substrates, and this vertical light-emitting device structure can be employed for many device applications. Electroluminescent devices, large scale photonics based on 1D semiconducting nanostructures, have been demonstrated using n-ZnO nanorod arrays grown vertically on p-type GaN epilayers. For the growth of ZnO nanorod arrays, we have employed catalyst-free metalorganic vapor phase epitaxy that has been established by our group. In addition, stable metal contacts on ZnO nanorod tips have been obtained by filling the free space between nanorods with insulating polymer and subsequent selective etching. These nanorod electroluminescent devices show high current density and strong electroluminescence even at a reverse-bias voltage of 3V. We believe this is presumably due to the enhanced tunneling effect on the nanosized p-n junction.

In 2000, we had found that vertically well-aligned ZnO nanorod arrays could be grown using metalorganic vapor phase epitaxy without using a metal-catalyst. We believed that this method has several advantages over other well-known metal catalyst assisted vapor-liquid-solid method for the growth of high-quality nanorod and heterostructures with an abrupt interface as well as vertical alignment of nanorods. Since we have been also much interested in semiconductor nanostructures and related electronic and photonic devices, after this discovery, we pushed ahead to realize the novel functional nanodevices and nanosystems utilizing our unique ZnO based nanorods and nanorod heterostructures. This project is one of the examples that make the most of the advantages of well-aligned ZnO nanorod arrays obtained by metalorganic vapor phase epitaxy.

We believe that this work can be used for practical applications for high efficiency light emitting devices and displays since the method used for this work can be used for mass-production. Cheap and high efficiency LED is so important in order to save energy and reduce consumption of fuel. Combining this "bottom-up" nanotechnology with conventional light-emitting device fabrication methods, we can help make the world a brighter place.