science-fiction fantasy of nanotechnology building
novel structures, devices, and materials at the atomic
or molecular scale is becoming a reality. For the
great potential of nanoscience and nanotechnology to be
fully realized, however, research efforts must cross many
disciplines, from electrical engineering, mechanical engineering,
materials science, and computer science to bioengineering,
chemistry, and physics.
is this cross-disciplinary approach fostered more than
at UC Berkeley. Each month, Lab Notes is proud
to present the work of nanotechnology researchers from
the College of Engineering and our collaborators across
LED There Be Light
by David Pescovitz
ideas in nanotechnology at UC Berkeley are helping usher in a new
age of environmentally-friendly, inexpensive, and innovative forms
of illumination. Based on technology similar to the ubiquitous red
Light Emitting Diodes (LEDs) found everywhere from alarm clocks
to car stereos, the new generation of solid-state lighting devices
are set to replace traditional incandescent bulbs for many applications.
At the Hearst Memorial Mining Building rededication reception, the Weber Group demonstrated this ring of white LEDs.
(Click for larger image.)
Peg Skorpinski photo
"The incandescent bulbs we use everyday to light our rooms
go back a century to Thomas Edison," says materials science
professor Eicke R. Weber, who's leading Berkeley's solid-state lighting
It's time for a change. By 2020, solid-state lighting devices could
cut electricity used for illumination by 50 percent and keep 28
million metric tons of carbon emissions out of the atmosphere each
year, according to a U.S. Department of Energy study.
Incandescent and fluorescent bulbs would have remained unchallenged
if it weren't for researchers at the Nichia Corporation in Japan
who in 1991 developed LEDs based on gallium nitride (GaN). This
particular semiconductor is capable of emitting blue light, which
combined with other colors or shined on yellow-emitting phosphors
produces the holy grail of white light. Already, these GaN-based
high-brightness LEDs can easily be spotted in efficient and ultra-bright
green traffic lights and some special-purpose flashlights.
we have these LEDs on the market, we dont understand fundamental
issues in how they work," Weber says. This lack of certainty
compounds the challenge of increasing the devices' brightness and
efficiency essential if LEDs are to have a chance at replacing
tried-and-true incandescent and fluorescent technology.
Professor Eicke Weber and his students also research new materials to improve photovoltaics (PV), or solar cells.
(Click for larger image.)
Peg Skorpinski photo
lie deep in the atomic structure of the semiconductor, Weber explains.
To build a GaN-based LED, two thin layers of the semiconducting
material laced, or doped, with different impurities that result
in specific electrical properties are sandwiched together. One layer
has a surplus of electrons while the other is rife with positive
charge-carriers, also known as holes. In between the two is a so-called
quantum well, containing a precise amount of the element Indium.
Passing current through the device forces the electrons and holes
into the quantum well between the layers where they recombine and
Weber and his team use techniques like electron microscopy and laser
spectroscopy enabled by UC Berkeley and the Lawrence Berkeley
Laboratory's state-of-the-art arsenal of nanotechnological tools
to better understand how the structure and chemistry of the
quantum wells may affect the efficiency and brightness of the light
generated by the LEDs.
"We can analyze the key parameters and go back to the growers
of the semiconductors and suggest changes, enabling them to fabricate
improved devices," says Weber, who collaborates on the research
with industrial partner Lumileds. Within this decade, he says, GaN-based
LED will be ready to be used for general illumination.
"If you create white light by combining red, green, and blue
LEDs, you could just as easily twist a knob next to your light switch
and change the color and mood of your room," Weber says.
Professor Eicke R. Weber's Home Page
LED research of the Weber Group
Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking
research underway today at the College of Engineering that will dramatically change our lives tomorrow.
Editor, Director of Public Affairs: Teresa Moore
Writer, Researcher: David Pescovitz
Designer: Robyn Altman
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