by Staff Writers
Munich, Germany (SPX) Feb 12, 2016
Physicists at the Technical University of Munich (TUM) have developed a nanolaser, a thousand times thinner than a human hair. Thanks to an ingenious process, the nanowire lasers grow right on a silicon chip, making it possible to produce high-performance photonic components cost-effectively. This will pave the way for fast and efficient data processing with light in the future.
Ever smaller, ever faster, ever cheaper - since the start of the computer age the performance of processors has doubled on average every 18 months. 50 years ago already, Intel co-founder Gordon E. Moore prognosticated this astonishing growth in performance. And Moore's law seems to hold true to this day.
But the miniaturization of electronics is now reaching its physical limits. "Today already, transistors are merely a few nanometers in size. Further reductions are horrendously expensive," says Professor Jonathan Finley, Director of the Walter Schottky Institute at TUM. "Improving performance is achievable only by replacing electrons with photons, i.e. particles of light."
Photonics - the silver bullet of miniaturization
Scientists at the TU Munich have now succeeded in this endeavor: Dr. Gregor Koblmuller at the Department of Semiconductor Quantum-Nanosystems has, in collaboration with Jonathan Finley, developed a process to deposit nanolasers directly onto silicon chips. A patent for the technology is pending.
Growing a III-V semiconductor onto silicon requires tenacious experimentation. "The two materials have different lattice parameters and different coefficients of thermal expansion. This leads to strain," explains Koblmuller. "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 in an ingenious way: By depositing nanowires that are freestanding on silicon their footprints are merely a few square nanometers. The scientists could thus preclude the emerging of defects in the GaAs material.
Atom by atom to a nanowire
To fulfil these conditions, the researchers had to develop a simple, yet sophisticated solution: "The interface between gallium arsenide and silicon does not reflect light sufficiently. We thus built in an additional mirror - a 200 nanometer thick silicon oxide layer that we evaporated onto the silicon," explains Benedikt Mayer, doctoral candidate in the team led by Koblmuller and Finley. "Tiny holes can then be etched into the mirror layer. Using epitaxy, the semiconductor nanowires can then be grown atom for atom out of these holes."
Only once the wires protrude beyond the mirror surface they may grow laterally - until the semiconductor is thick enough to allow photons to jet back and forth to allow stimulated emission and lasing. "This process is very elegant because it allows us to position the nanowire lasers directly also onto waveguides in the silicon chip," says Koblmuller.
Basic research on the path to applications
The team has just published its first successes in this direction. And they have set their sights firmly on their next goal: "We want to create an electric interface so that we can operate the nanowires under electrical injection instead of relying on external lasers," explains Koblmuller.
"The work is an important prerequisite for the development of high-performance optical components in future computers," sums up Finley. "We were able to demonstrate that manufacturing silicon chips with integrated nanowire lasers is possible."
Technical University of Munich
Space Technology News - Applications and Research
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