LOS
ALAMOS, N.M., May 17, 2005 -- A team of University
of California scientists at Los Alamos National
Laboratory have developed the first completely
inorganic, multi-color light-emitting diodes (LEDs)
based on colloidal quantum dots encapsulated in
a gallium nitride (GaN) semiconductor. The work
represents a new "hybrid" approach
to the development of solid-state lighting. Solid-state lighting offers the
advantages of reduced operating expenses, lower energy consumption and more
reliable performance.
In research published in the current issue of the scientific journal Nano Letters,
the team reports on the first successful demonstration of electroluminescence
from an all-inorganic, nanocrystal-based architecture where semiconductor nanocrystals
are incorporated into a p-n junction formed from semiconducting GaN injection
layers. The new LEDs utilize a novel type of color-selectable nanoemitters, colloidal
quantum dots, and makes use of emerging GaN manufacturing technologies.
According to Klimov, who leads the nanocrystal-LED research effort, "numerous
technologies could benefit from energy efficient, color-selectable solid-state
lighting sources ranging from automotive and aircraft instrument displays to
traffic signals and computer displays. Semiconductor nanocrystals, known also
as quantum dots, are attractive nanoscale light emitters that combine size-controlled
emission colors and high emission efficiencies with chemical flexibility and
excellent photostability. The use of nanocrystals in light-emitting technologies
has, however, always been hindered by the difficulty of making direct electrical
connections to the nanocrystals. By putting the quantum dots between GaN injection
layers, we've gotten around this difficulty."
The secret to making the electrical connection to the quantum dots is the use
of a technique developed at Los Alamos by Mark Hoffbauer and his team that utilizes
a beam of energetic, neutral nitrogen atoms for growing GaN films. The technique,
called ENABLE (for Energetic Neutral Atom Beam Lithography/Epitaxy), allows for
the low-temperature encapsulation of nanocrystals in semiconducting GaN without
adversely affecting their luminescence properties. By encapsulating one nanocrystal
layer or two layers of nanocrystals of different sizes, the researchers have
demonstrated that their LEDs can emit light of either a single color or two different
colors. The two color-operation regime is an important step toward creating devices
that produce white light.
The development of the multicolor LEDs is the result of a collaboration between
two Laboratory research groups: Klimov's quantum-dot team and Hoffbauer's team
developing advanced nanoscale processing technologies. Laboratory researchers
critical to the project's success also include Alexander Mueller, Melissa Petruska,
Marc Achermann, Donald Werder, and Elshan Akhadov. Daniel Koleske of Sandia National
Laboratories provided the GaN substrates used for the LED structures.
The Los Alamos Laboratory-Directed Research and Development (LDRD) program provided
funding for the Los Alamos work as an Exploratory Research (ER) project. The
research fits into a broader area of expertise that Los Alamos National Laboratory
maintains in the field of nanotechnology in general, and quantum dot research
in particular.
Los Alamos National Laboratory is operated by the
University of California for the National Nuclear
Security Administration of the U.S. Department of
Energy and works in partnership with NNSA's Sandia
and Lawrence Livermore national laboratories to support
NNSA in its mission.
Los Alamos enhances global security by ensuring
the safety and reliability of the U.S. nuclear
deterrent, developing technologies to reduce
threats from weapons of mass destruction, and
solving problems related to defense, energy,
environment, infrastructure, health and national
security concerns.
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