Exciton transistors could create the energy-efficient electronics of the future

Last year, researchers at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland developed a new type of transistor — one based on excitons, a special type of quasiparticle — which could be used in the future to make electronic devices smaller, faster, and more efficient. And now the same team has made another breakthrough by discovering new properties of excitons.

An exciton is a subatomic quasiparticle, meaning that it is not a particle in itself, but rather an interaction between two particles. In the case of excitons, they are made up of a bound pair of one electron and one electron hole. (An electron hole is a space in an atom where there is no electron but where one could exist.) The electron and electron hole become linked together when the electron absorbs a photon which gives it a higher level of energy, and the energetic electron moves position and leaves behind an electron hole. The electron is negatively charged and the hole that it leaves behind is positively charged, so the two bond in a process called the Coulomb attraction and form an exciton.

The EPFL team developed a transistor which used excitons instead of electrons. The advantage of this is that the exciton transistor can operate effectively at room temperature, while traditional electron transistors always produce heat when they operate. As transistors are a key component of circuits, having them produce no extra heat would potentially mean a big increase in energy efficiency and no need for large and bulky heat sinks or other cooling in electronic devices.

The latest breakthrough scientists have made is in controlling the properties of excitons. They have found a way to change the polarization of the light generated by the exciton by manipulating a property known as its “valley.” The valley is the maximum and minimum energies that a particle can express, and the valleys of electrons can be used to store information in a field known as “valleytronics” which could extend the ending of Moore’s Law. In the case of excitons, these valleys can be used to code and process information on a minuscule scale.

“Linking several devices that incorporate this technology would give us a new way to process data,” Andras Kis, head of EPFL’s Laboratory of Nanoscale Electronics and Structures, explained in a statement. “By changing the polarization of light in a given device, we can then select a specific valley in a second device that’s connected to it. That’s similar to switching from 0 to 1 or 1 to 0, which is the fundamental binary logic used in computing.”