New phase-change material lights the way to all-optical, super-fast computing.

New phase-change material lights the way to all-optical, super-fast computing.

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British researchers have created a new material that could allow for the creation of all-optical computers — computers that are orders of magnitude faster and power efficient than today’s hot, sweaty electronic beasts. This isn’t some crazy, hard-to-fabricate material like graphene, either — we’re talking about a special breed of chalcogenide glass.

You’d be forgiven for not knowing what a chalcogenide glass is, but trust me, you’ve all seen one — and probably made extensive use of them, too. Chalcogenide glasses are a family of (rather oddly behaved) materials that can readily change state between glassy and crystalline, which also changes their optical and and electrical properties. The recording layer of every rewritable CD and DVD consists of a chalcogenide glass (usually germanium-antimony-tellurium, GST) that changes state between glass and crystal when it’s struck by powerful laser, or can have its state read by a weaker laser, and can thus be used to store and retrieve binary data. Chalcogenide glasses are also used in modern, super-fast phase-change memory (pictured above), where a small heating element is used instead of a laser to change the state of a memory cell.

A slide showing the two different phases/states for a chalcogenide glass. (This is for phase-change memory, but it’s much the same concept.)

In modern computing, there’s a strong dichotomy between optical and electronic systems. On the one hand, almost every computer is governed by the flow of electricity — along copper wires and over transistors. The flow of electricity creates a lot of heat, though, which limits how fast a computer can operate — and separately, electrical resistance/impedance makes electricity poorly suited for long-range transmission (you need to pump the voltage up to go more than a few meters, and that causes issues). This is why we use lasers and optical fibers for backbone internet connections — it’s both faster and more efficient.
Read: The secret world of submarine cables
We would love to use lasers instead of electricity inside our computers, but a) it’s hard to build tiny lasers that fit on a small silicon chip, and b) optical transistors with comparable performance to the latest 14nm FinFET transistors are hard to come by. Now, researchers at the University of Surrey, University of Cambridge, and University of Southampton in England may have come up with a solution that will allow for all-optical computers — a single component that can produce light, guide light, store light, and detect light. [Research paper: doi:10.1038/ncomms6346 / pre-print PDF]

An IBM chip that integrates both electronic and photonic components – a rare example of scaling lasers down small enough to fit on a chip die.

Basically, the British researchers have taken a chalcogenide glass — which are always p-type semiconductors — and managed to turn it into an n-type semiconductor. (In this case, they germanium telluride (GeTe) and ionically doped it with bismuth to create an n-type). This allowed them to build a p-n junction — the primary building block of almost every semiconductor device, from transistors to LEDs to photovoltaic cells.
The research paper seems to stop short of actually using these chalcogenide p-n junctions, merely marveling at the fact that they’ve managed to create them in the first place — but the accompanying press release is pretty optimistic about their world-changing applications. “The challenge is to find a single material that can effectively use and control light to carry information around a computer. Much like how the web uses light to deliver information, we want to use light to both deliver and process computer data,” says project leader Richard Curry. “In doing so, this could transform the computers of tomorrow, allowing them to effectively process information at much faster speeds.”
As for when we’ll actually see chalcogenide transistors and all-optical computers, we’re probably talking years. Phase-change memory, however, which provides non-volatile storage with performance that’s better than DRAM, is right on the cusp of commercial availability.