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Date: 07-02-11

Engineers at UC Berkeley find a way to build nano laser on silicon surface


Research Engineers at the University of California, Berkeley able to grow InGaAs (Indium Gallium Arsenide) nanopillars on silicon surface at temperature of 400 degrees Celsius. This research aimed at utilizing present semiconductor equipment to make complex processor chips with on-chip and chip-to-chip opto communication interface. The 32 bit and 64 bit processors can get rid of complex copper wire buses both on chip and on the PCB by employing serial optical links. Optical links are faster and are noise free. This also enables simple board design.

But the challenge to the semiconductor industry is building light emitting lasers using the popular silicon semiconductor material or placing and fabricating a opto-semiconductor material (such as InGaAs) based light emitting laser over a present Silicon wafers using the equipment which is already used in making processor chips. Forcing silicon to emit light is more challenging than building nano sized III-V semiconductor devices such as GaAs, InGaAs, and GaN on silicon surface.
Overall idea is to reduce the manufacturing cost in developing chips with on-chip photon emitters and receivers.

Engineers at the University of California, Berkeley have grown nanolasers directly onto a silicon surface. Their research work is published in 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 principal investigator, Connie Chang-Hasnain, UC Berkeley professor of electrical engineering and computer sciences.

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


"Today's massive silicon electronics infrastructure is extremely difficult to change for both economic and technological reasons, so compatibility with silicon fabrication is critical," said Chang-Hasnain. "One problem is that growth of III-V semiconductors has traditionally involved high temperatures - 700 degrees Celsius or more - that would destroy the electronics. Meanwhile, other integration approaches have not been scalable."


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

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

Once the nanopillar was made, the researchers showed that it could generate near infrared laser light - a wavelength of about 950 nanometers - at room temperature. The hexagonal geometry dictated by the crystal structure of the nanopillars creates a new, efficient, light-trapping optical cavity. Light circulates up and down the structure in a helical fashion and amplifies via this optical feedback mechanism.

The unique approach of growing nanolasers directly onto silicon could lead to highly efficient silicon photonics, the researchers said. They noted that the miniscule dimensions of the nanopillars - smaller than one wavelength on each side, in some cases - make it possible to pack them into small spaces with the added benefit of consuming very little energy

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

"This is the first bottom-up integration of III-V nanolasers onto silicon chips using a growth process compatible with the CMOS (complementary metal oxide semiconductor) technology now used to make integrated circuits," said Chang-Hasnain. "This research has the potential to catalyze an optoelectronics revolution in computing, communications, displays and optical signal processing. In the future, we expect to improve the characteristics of these lasers and ultimately control them electronically for a powerful marriage between photonic and electronic devices."

The research is supported by Defense Advanced Research Projects Agency and a Department of Defense National Security Science and Engineering Faculty Fellowship of U.S.

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