New Laser Data Transmission for Computer Chips Uses Only a Fraction of the Energy

Schematic structure of the germanium-tin (GeSn) laser, applied directly onto the silicon wafer (blue) by using an intermediate layer of pure germanium (orange).

An international team of scientists constructs the first germanium-tin semiconductor laser for silicon chips

Scientists from Forschungszentrum Jülich and the Paul Scherrer Institute in Switzerland in cooperation with international partners have presented the first semiconductor consisting solely of elements of main group IV. As a consequence, the germanium-tin (GeSn) laser can be applied directly onto a silicon chip and thus creates a new basis for transmitting data on computer chips via light: this transfer is faster than is possible with copper wires and requires only a fraction of the energy. The results have been published in the journal Nature Photonics.

The transfer of data between multiple cores as well as between logic elements and memory cells is regarded as a bottleneck in the fast-developing computer technology. Data transmission via light could be the answer to the call for a faster and more energy efficient data flow on computer chips as well as between different board components. “Signal transmission via copper wires limits the development of larger and faster computers due to the thermal load and the limited bandwidth of copper wires. The clock signal alone synchronizing the circuits uses up to 30% of the energy – energy which can be saved through optical transmission,” explains Prof. Detlev Grützmacher, Director at Jülich’s Peter Grünberg Institute.

Some long-distance telecommunication networks and computing centres have been making use of optical connections for decades. They allow very high bandwidths even over long distances. Through optical fibres, signal propagation is almost lossless and possible across various wavelengths simultaneously: a speed advantage which increasingly benefits both micro- and nanoelectronics. “The integration of optical components is already well advanced in many areas. However, in spite of intensive research, a laser source that is compatible with the manufacturing of chips is not yet achievable,” according to the head of Semiconductor Nanoelectronics (PGI-9).

Suitable material for chip production

The basis of chip manufacturing is silicon, an element of main group IV of the periodic table. Typical semiconductor lasers for telecommunication systems, made of gallium arsenide for example, however, are costly and consist of elements from main groups III or V. This has profound consequences on the crystal properties. Such laser components cannot therefore be applied directly onto silicon. They have to be produced externally at great effort and subsequently glued to the silicon wafer. However, the lifetime of this kind of component is greatly reduced due to the fact that the thermal expansion coefficients of these elements are significantly different from that of silicon.

In contrast, semiconductors of main group IV – to which both silicon and germanium belong – can be integrated into the manufacturing process without any major difficulties. Neither element is very efficient as a light source, however. They are classed among the indirect semiconductors. In contrast to direct semiconductors, they emit mostly heat and only a little light when excited. That is why research groups all over the globe are intensively pursuing the objective of manipulating the material properties of germanium so that it would be able to amplify optical signals and thus make it a usable laser source.

Read more: New Laser for Computer Chips