Researchers solve an old problem in optical information processing.
Computers process information based on electrons—particles representing binary bits via their respective charges. These electrons are shuttled around microprocessors and memory banks via conductive "wires" rendered incomprehensibly small thanks to nanoscale lithographic techniques. In the grand scheme of information, however, those pathways are still enormous, like building subway tunnels for cockroaches.
A reasonable next step beyond electrons and electricity, generally, would be optics: information via photons, or light particles. This is a possibility—or perhaps inevitability—being aggressively researched by physicists and materials scientists. According to a paper published Friday in the journal Nature Communications, computing may be one step closer to the photonic information age with the apparent resolution of one of the technology's deepest problems: fine-tuning the electrical conductivity of glass.
"The challenge is to find a single material that can effectively use and control light to carry information around a computer," noted Richard Curry, the current study's lead investigator and a physicist the the University of Surrey, in a statement. "Much like how the web uses light to deliver information, we want to use light to both deliver and process computer data."
"This has eluded researchers for decades," Curry said, "but now we have now shown how a widely used glass can be manipulated to conduct negative electrons, as well as positive charges, creating what are known as 'pn-junction' devices."
Now we have now shown how a widely used glass can be manipulated to conduct negative electrons, as well as positive charges.
The p-n junction problem arises from the nature of semiconductors known as extrinsic semiconductors. These involve materials that have been "doped" with some other material, or impurity, to give the semiconductor a particular conductivity property. The new impurities change the electron landscape of the material being doped, either adding or subtracting electrons and electron holes (empty slots within the orbits or electron shells of given atom that might otherwise contain a particle).
Getting the right sort of conductivity for optical information devices has involved both the usage of very high levels of doping agents and very high temperatures. This is true, in particular, for a material called chalcogenide glass, the preferred medium for photonic integrated chips and other optical computing applications.
Chalcogenides act as so-called network solids, in which a macroscopic material acts as one large single molecule. This sort of material has the advantage of being able to conduct light across a relatively wide range of bandwidths, while chalcogenides have unique properties allowing for the usage of electron beams to control the optical refraction of a material, among other handy things.
The catch is that chalcogenides are p-type conductors. That is, they're characterized by more electron holes than electrons, with the "p" referring to the positive charge of the holes. The problem here is that they resist interfacing with the other variety of extrinsic semiconductor: n-types. So far, it's been extraordinarily difficult to dope a chalcogenides glass to act as a n-type semiconductor.
"Electronic applications [of chalcogenides] are limited as a consequence of their almost universally unmodifiable p-type conductivity," the current study notes. What's more, the authors add, the only existing modification technique, involving high temperatures and high concentrations of doping agents, is incompatible with current integrated circuit manufacturing techniques. So we're stuck with electrons.
Or at least we were. Curry and his team have for the first time successfully doped chalcogenide glass in such a way as to allow for standard-ish integrated circuit manufacturing involving non-extreme temperatures and relatively small amounts of doping agents. The process involves the implantation of ions of the element bismuth in the glass in concentrations of only .6 percent of what was previously needed.
The result is a material that's highly refractive, thermally stable, and that requires just a tiny fraction of the electronic current needed to maintain optical information, compared to other materials.
Curry expects the technology to be built into common computers within 10 years, and, well before that, a long in-development computer memory technology called CRAM. CRAM is essentially where a chalcogenide glass has its phases swapped around between crystalline and amorphous with the application of heat. In terms of speed, CRAM could potentially beat out current hard drive technology (including Flash memory) many thousands of times over.