Munich researchers develop nanolasers for silicon photonics

Scientists have developed a process to deposit nano-lasers directly onto silicon chips, paving the way for fast and efficient data processing using silicon photonics.

Physicists at the Technical University of Munich (TUM) have developed a nano-laser one thousand times thinner than a human hair. This process deposits the nano-wire lasers directly onto the chip, making it possible to produce high-performance, cost-effective photonic components.

While transistor developers have been able to rely on the miniaturisation of transistor designs to produce reliable, incremental performance increases in computing power, the hard limits of Moore’s law are fast approaching – making further reductions in the size of transistors time-consuming and increasingly expensive.

Professor Jonathan Finley, director of the Walter Schottky Institute at TUM, said: ‘Already, transistors are merely a few nanometres in size. Further reductions are horrendously expensive. Improving performance is achievable only by replacing electrons with photons, i.e. particles of light.’

Data transmission and processing with light has the potential of breaking the barriers of current electronics. In fact, the first silicon-based photonics chips already exist. However, the sources of light for the transmission of data must be attached to the silicon using complicated and elaborate manufacturing processes.

The researches from TU Munich, led by Dr Gregor Koblmüller and Jonathan Finley at the Department of Semiconductor Quantum-Nanosystems, part of the Walter Schottky Institute at TU Munich, developed a process to deposit nano-lasers directly onto silicon chips – alleviating the increased costs associated with making smaller transistors. A patent for the technology is pending.

Traditionally, growing a III-V semiconductor (such as Gallium-Arsenide) on silicon requires complicated and time-consuming development that is restricted its use in commercial applications.

‘The two materials have different lattice parameters and different coefficients of thermal expansion. This leads to strain,’ explained Koblmüller. ‘For example, conventional planar growth of gallium arsenide onto a silicon surface results therefore in a large number of defects.’

The TUM team solved this problem by depositing freestanding nano-wires, with a footprint of only a few nanometres, directly onto the silicon substrate. This process helped the scientists to reduce, and in some cases remove, the defects associated in the production of GaAs semiconductors. The next step for the project was to convert the nano-wire into a vertical-cavity laser.

‘The interface between gallium arsenide and silicon does not reflect light sufficiently. We thus built in an additional mirror – a 200 -nanometre silicon oxide layer that we evaporated onto the silicon,’ said Benedikt Mayer, doctoral candidate in the team led by Koblmüller and Finley. ‘Tiny holes can then be etched into the mirror layer. Using epitaxy, the semiconductor nano-wires can then be grown, atom for atom, out of these holes.’

‘We want to create an electric interface so that we can operate the nano-wires under electrical injection instead of relying on external lasers,’ stated Koblmüller.

‘The work is an important prerequisite for the development of high-performance optical components in future computers. We were able to demonstrate that manufacturing silicon chips with integrated nano-wire lasers is possible' concluded Finley.

The research was funded by the German Research Foundation (DFG) through the TUM Institute for Advanced Study, the Excellence Cluster Nanosystems Initiative Munich (NIM) and the International Graduate School of Science and Engineering (IGSSE) of the TUM, as well as by IBM through an international postgraduate program.

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