Scientists working at the University of Cambridge have used a form of liquid light to create a semiconductor switch that is so small that it not only blurs the distinction between light and electricity, but could also enable the development of much faster and smaller electronic components well into the future.

With the limits of Moore's Law looming closer day by day, the demand for faster, smaller electronics ever increasing, and microelectronics reaching the point where quantum effects are seriously challenging the continued use of electrons as a transporter of data, researchers the world over are exploring ways to solve these problems.


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With contemporary methods used to convert between electrical signals and optical ones considered largely inefficient, University of Cambridge researchers believe that it would be better simply to cut out the middleman and mix the two together. In a quest to achieve this, the researchers created a switch using a new state of matter known as a Polariton Bose-Einstein condensate to combine electric and optical signals, while consuming infinitesimally small quantities of energy in the process.

"The polariton switch unifies the best properties of electronics and optics into one tiny device that can deliver at very high speeds while using minimal amounts of power," says Dr Alexander Dreismann from Cambridge's Cavendish Laboratory.

To create a Polariton Bose-Einstein condensate, laser light is first captured between mirrors in a microcavity just a few microns in size. Here the light interacts with thin sections of semiconductor material to produce a half-light, half-matter combination of quasi-particles known as a polariton, which are made up of semiconductor excitons (excited electrons bound to the hole produced by their excitation) and photons .

If large amounts of these polaritons are generated all at once in a confined space, they tend to clump together and condense like water vapor does when it encounters a cool surface. The light-matter fluid that forms at this point is also imparted with a particular spin, where it can spin clockwise (up) or anticlockwise (down). To make the direction of spin controllable, and therefore usable in an electronic context, the researchers induced an electric field within the condensate, making it possible to switch between up and down states at will. As the polariton fluid also produces light as it rotates, the researchers believe that spin encoded light could be used to convert electrical data to optical signals that can be sent through optical fibers.

"We have made a field-effect light switch that can bridge the gap between optics and electronics," says Dr Hamid Ohadi, from the Cavendish Laboratory. "We're reaching the limits of how small we can make transistors, and electronics based on liquid light could be a way of increasing the power and efficiency of the electronics we rely on."

Just like other forms of energy that create strange and interesting amalgams between energy and matter at the nanoscale, such as the newly-discovered topological plexciton, polariton fluid promises to greatly increase electronic efficiency, but it also only tends to work at cryogenic temperatures. As such, the Cavendish Laboratory scientists are researching other types of material that exhibit the same properties at ambient temperatures, in the hope of commercializing the technology and integrating it with existing devices.

The researchers say the fact the prototype was based on well-established fabrication technology gives the prototype the potential to be scaled up, which is a key aspect in terms of future mass production potential.

The results of this research were recently published in the journal Nature Materials.

Source: University of Cambridge