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Scientists at Harvard, in collaboration with researchers from the German universities of Jena, Gottingen, and Bremen, have developed a technique for fabricating nanowire photonic and electronic integrated circuits that may one day be suitable for high-volume commercial production.

More broadly, because nanowires can be made of materials commonly used in electronics and photonics, they hold great promise for integrating efficient light emitters, from ultraviolet to infrared, with silicon technology.

While semiconductor nanowires — rods with an approximate diameter of one-thousandth the width of a human hair — can be easily synthesized in large quantities using inexpensive chemical methods, reliable and controlled strategies for assembling them into functional circuits have posed a major challenge. However, by incorporating spin-on glass technology, used in silicon integrated circuits manufacturing, and photolithography, transferring a circuit pattern onto a substrate with light, the team demonstrated a reproducible, high-volume, and low-cost fabrication method for integrating nanowire devices directly onto silicon.

The structure of the team's nanowire devices is based on a sandwich geometry: A nanowire is placed between the highly conductive substrate that functions as a common bottom contact and a top metallic contact, using spin-on glass as a spacer layer to prevent the metal contact from shorting to the substrate. As a result, current can be uniformly injected along the length of the nanowires. These devices can then function as light-emitting diodes, with the color of light determined by the type of semiconductor nanowire used.

To demonstrate the potential scalability of their technique, the team fabricated hundreds of nanoscale ultraviolet light-emitting diodes using zinc oxide nanowires on a silicon wafer.

Plans are afoot to further refine the method so that there will be electrically contacting nanowires over entire wafers. Such an advance could lead to the development of a completely new class of integrated circuits, such as large arrays of ultra-small nanoscale lasers that could be designed as high-density optical interconnects or be used for on-chip chemical sensing.