Nanoscale Semiconductors Show Dramatic Increase in Coupling Strength

Researchers at the University of Pennsylvania have showed that polaritons exhibit improved coupling strength when trapped within nanoscale semiconductors, which can prove useful for the advancement of the photonics field by manufacturing compact and rapid circuits that utilize light and not electricity.

A computer simulation of a one-dimensional cavity wave in a 200nm nanowire

A major factor to be considered while developing photonic devices is high coupling strength of light and matter. Such photonic devices would use light rather than electricity and thus be quicker and consume low power when compared to other electronic equipment. It was believed that the coupling strength displayed within bulk semiconductor materials was a fixed characteristic of the material they were comprised of. However, Agarwal's team demonstrated that, with proper finishing and fabrication, the coupling strength can be increased further.

Agarwal stated that the light-matter coupling strength is steady for semiconductors of bulk sizes to one micron. He also added that the coupling strength increases significantly for semiconductors below 500 nm.

The difference in behavior was due to the change in material size. A bulk material was found to exhibit different properties when compared to the same material at the nanoscale level.

Agarwal explained that the surface is not very crucial in determining the device's properties while dealing with large-sizes as the surface to volume ratio is negligible. However, while fabricating a very small structure of the order of 100 nm, the surface to volume ratio increases significantly and the alterations in the surface determine the properties of the device, he says.

Agarwal mentioned that their cadmium sulfide nanowires are obtained not by the process of etching but are instead self-assembled. They developed methods of surface passivation to overcome the challenges of surface quality. They enhanced the optical properties of nanowires by growing a silicon oxide shell coating on the surface, stated Agarwal.

The electrical gaps present on the surface of the nanowires are filled by the oxide shell, thus preventing trapping of the excitons. The increase in coupling strength paves the way for developing nanophotonic circuit devices and elements.

Source: http://www.upenn.edu/

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