Quantum leap for silicon

Silicon, the stalwart of the electronics industry, has been given a new lease of life with news of a silicon-based material that converts electronic data into optical data with unprecedented efficiency.

The best way to transfer large amounts of data quickly is with light beams. Silicon, which dominates the electronics industry, can’t emit enough light to be an effective optical transmitter. As electronics devices outgrow silicon’s capabilities to pass on data electronically, alternative materials are needed. The latest, a germanium-silicon semiconductor switch, has been developed by Yu-Hsuan Kuo and colleagues at Stanford University, US.

Kuo has grown thin germanium layers on silicon wafers. The layers do not give out light themselves but can absorb or transmit incoming laser light depending on the operating voltage. This wasn’t possible in a silicon-based material before.

The energy levels in the thin layers are affected by an applied electric field - a phenomenon known as the quantum-confined Stark effect. ’What it amounts to is that you get a larger change in absorption [of laser light] than you would do if you had a thick layer of the same material,’ said Gareth Parry, a semiconductor expert from Imperial College London, UK. ’It means you have a material whose absorption you can switch off and on at a given wavelength,’ he said. This effectively produces a switchable optical signal from the germanium-silicon layers if a laser is shone on them. 

Kuo says the device is ready for mass production, but Parry is more cautious. Converting electronic signals into optical signals with a silicon-based device is a major step, said Parry, but ’it’s likely to be a technology that gets improved on and developed for initially high performance computing or very complex electronics systems.’ 

The silicon industry would have to change the way it made circuits in order for these devices to become commonplace, and Parry doesn’t see that happening for at least 10 years. ’This actually requires a major step. And the silicon industry is quite conservative. It doesn’t like changing anything,’ he said. Katharine Sanderson