Nanolasers Grown on Silica

This is an important advance thatallows photonic methods to now be integrated directly with well knownelectronic methods on the same chip. Again we leap ahead in the march to advance Moore’s law.

It also brings us closer to apurely optical microprocessor which is surely our present goal.

With that temperature problemsare going to go away and we can imagine producing a three dimensionalarchitecture able to shed heat fast enough. Perhaps then we can have the most powerful computer packed in a gem likestone.

It really is a fantasticachievement well imagined a couple of generations ago and now even in sight.

Engineers Grow Nanolasers On Silicon, Pave Way For On-Chip Photonics

by Staff Writers

Berkeley CA(SPX) Feb 07, 2011

The unique structure of the nanopillars grown by UC Berkeleyresearchers strongly confines light in a tiny volume to enable subwavelengthnanolasers. Images on the left and top right show simulated electric fieldintensities that describe how light circulates helically inside thenanopillars. On the bottom right is an experimental camera image of laser lightfrom a single nanolaser. Credit: Connie Chang-Hasnain Group

Engineers at the University of California,Berkeley, have found a way to grow nanolasers directly onto a silicon surface,an achievement that could lead to a new class of faster, more efficient microprocessorrs,as well as to powerful biochemical sensors that use optoelectronic chips.

They describe their work in a paper to be published Feb. 6 in anadvanced online issue of the journal Nature Photonics.

"Our results impact a broad spectrum of scientific fields,including materials science, transistor technology, laser science,optoelectronics and optical physics," said the study's principalinvestigator, Connie Chang-Hasnain, UC Berkeley professor of electricalengineering and computer sciences.

The increasing performance demands of electronics have sent researchersin search of better ways to harness the inherent ability of light particles tocarry far more data than electrical signals can. Optical interconnects are seenas a solution to overcoming the communications bottleneck within and betweencomputer chips.

Because silicon, the material that forms the foundation of modernelectronics, is extremely deficient at generating light, engineers have turnedto another class of materials known as III-V (pronounced"three-five")semiconductors tocreate light-based components such as light-emitting diodes (LEDs)and lasers.

But the researchers pointed out that marrying III-V with silicon tocreate a single optoelectronic chip has been problematic. For one, the atomicstructures of the two materials are mismatched.

"Growing III-V semiconductor films on silicon is like forcing twoincongruent puzzle pieces together," said study lead author Roger Chen, aUC Berkeley graduate student in electrical engineering and computer sciences."It can be done, but the material gets damaged in the process."

Moreover, the manufacturing industry is set up for the production ofsilicon-based materials, so for practical reasons, the goal has been tointegrate the fabrication of III-V devices into the existing infrastructure, theresearchers said.

"Today's massive silicon electronics infrastructure is extremelydifficult to change for both economic and technological reasons, socompatibility with silicon fabrication is critical," said Chang-Hasnain.

"One problem is that growth of III-V semiconductors hastraditionally involved high temperatures - 700 degrees Celsius or more - thatwould destroy the electronics. Meanwhile, other integration approaches have notbeen scalable."

The UC Berkeley researchers overcame this limitation by finding a wayto grow nanopillars made of indium gallium arsenide, a III-V material, onto asilicon surface at the relatively cool temperature of 400 degrees Celsius.

"Working at nanoscale levels has enabled us to grow high qualityIII-V materials at low temperatures such that silicon electronics can retaintheir functionality," said Chen.

The researchers used metal-organic chemical vapor deposition to growthe nanopillars on the silicon. "This technique is potentially massmanufacturable, since such a system is already used commercially to make thinfilm solar cells and light emitting diodes," said Chang-Hasnain.

Once the nanopillar was made, the researchers showed that it couldgenerate near infrared laser light - a wavelength of about 950 nanometers - at roomtemperature.

The hexagonal geometry dictated by the crystal structure of thenanopillars creates a new, efficient, light-trapping optical cavity. Lightcirculates up and down the structure in a helical fashion and amplifies viathis optical feedback mechanism.

The unique approach of growing nanolasers directly onto silicon couldlead to highly efficient silicon photonics, the researchers said. They notedthat the miniscule dimensions of the nanopillars - smaller than one wavelengthon each side, in some cases - make it possible to pack them into small spaceswith the added benefit of consuming very little energy

"Ultimately, this technique may provide a powerful and new avenuefor engineering on-chip nanophotonic devices such as lasers, photodetectors, modulatorsand solar cells," said Chen.

"This is the first bottom-up integration of III-V nanolasers ontosilicon chips using a growth process compatible with the CMOS (complementarymetal oxide semiconductor) technology now used to make integrated circuits,"said Chang-Hasnain.

"This research has the potential to catalyze an optoelectronicsrevolution in computing, communications, displays and optical signalprocessing. In the future, we expect to improve the characteristics of theselasers and ultimately control them electronically for a powerful marriagebetween photonic and electronic devices."

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