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Light-Emitting Particles Yield Faster Computing
schliz writes to tell us that researchers at the University of California San Diego are developing new transistors based on particles called 'excitons' in an attempt to speed up the interaction between computing and communications signals. "Excitons are formed by linking a negatively-charged electron with a positively-charged 'hole'. An exciton decays when the electron and hole combine, emitting a flash of light in the process. By joining exciton-based transistors to form several types of switches, the UCSD physicists were able to achieve switching times on the order of 200 picoseconds."
The original source for this particular experiment is this Science article. The submission was terrible. Press releases should be banned from any site which claims to have intelligent discussion.
An indirect exciton (what these guys are using) is made using three layers. In one layer, you have extra electrons (negative charges). In another layer, you have a lack of electrons (positive charges). In between those two is an insulating layer. If you tune the charge densities and some other parameters (temperature, for example), you can get the positive and negative charges in the two charged layers to align into pairs. Each pair is an exciton.
A normal exciton is a pair like this without the insulator between them. As you might imagine, they don't last very long and pretty much instantly combine. When an exciton combines, it gives off light at a very particular wavelength. Conversely, when light at that particular wavelength is adsorbed by the material, it creates an exciton.
You could imagine creating an exciton with light, making it an indirect exciton (so that it's stable), doing something with it, and then making it a normal exciton again and waiting the picosecond or so it takes for it to collapse and emit light. That's basically what they've done... but it's much harder than I've made it sound.