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.
