A major bottleneck to modern computing power is
latency -- the time it takes for a CPU to communicate with other devices like a
graphics chip, or memory. One possible solution is to switch from using
an electrical bus to an
optical one. In well-made glass, light can travel at nearly
two-thirds its speed in the vacuum an astonishingly fast transfer speed.
The key, though, is that you need something to emit a high intensity
burst of light (a laser pulse).
Researchers at the University of California,
Berkeley have completed a work that inches the computer industry closer to this
dream. They've developed a new process that will allow laser-emitting
nanopillars to be directly grown onto silicon at milder conditions
than in past work.
Silicon itself is remarkably bad at emitting
light, so researchers must use alternate semiconductors. One of the most
promising candidates is so-called "III-V"
semiconductors, which consist of one transition metal element, and one
semiconducting element from the fifth group of the periodic table, like
But growing these elements onto silicon using
traditional process technologies has been pretty much impossible, due to the
mismatch complexities and high temperature constraints.
The study's lead author, Roger Chen [profile], a
UC Berkeley graduate student in electrical engineering and computer sciences,
release], "Growing III-V semiconductor films on silicon is like
forcing two incongruent puzzle pieces together. It can be done, but the
material gets damaged in the process."
Adds Connie Chang-Hasnain [profile], UC Berkeley
professor of electrical engineering and computer sciences who served as the
project's principle investigator; "Today's massive silicon electronics
infrastructure is extremely difficult to change for both economic and
technological reasons, so compatibility with silicon fabrication is critical.
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
The researchers developed a process to deposit
nanopillars of indium gallium arsenide, a III-V semiconductor, at only 400
degrees Celsius. The metal-organic chemical vapor deposition method
used is already in commercial use in the solar cell and LED industry.
The resulting nanopillar structure is hexagonal
and amplifies an infrared (950 nm) laser signal. Spiral helically up the
pillars, the laser is emitted at their ends. This laser-cavity mechanism
is complex theoretically, but the bottom line is the researchers have created
an on-chip laser that's grown using more affordable process.
States Professor Chang-Hasnain, "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. 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
The study on the work was published [abstract]
in the prestigious peer-reviewed journal Nature
Photonics. The work was funded by a grant from The Defense
Advanced Research Projects Agency (DARPA) and a Department of Defense National
Security Science and Engineering Faculty Fellowship.