ATHENS,
Ohio — For almost a decade, scientists thought
they understood the surface structure of cubic gallium
nitride, a promising new crystalline semiconductor.
Research by an interdisciplinary team of nanoscientists
from Ohio University and the Universitat Autònoma
de Barcelona, however, turns that idea on its head.
Their
study published in the Sept. 30 online issue of
the journal Physical Review Letters provides a
fresh – and they argue, more accurate – look at
the surface structure of the crystalline material,
which could be used in lasers and other electronic
devices.
Nancy
Sandler, an assistant professor of physics and
astronomy at Ohio University, and Pablo Ordejón,
a Barcelona professor specializing in the algorithm
used in the project, calculated several properties
using the currently accepted model and obtained new
images of the crystal's surface. Experimentalists
Hamad Al-Brithen and his Ph.D. adviser Arthur Smith,
Ohio University associate professor of physics and
astronomy, recently had used scanning tunneling microscopy
to capture an image of the surface.
When
they compared the model image with the experimental
image, the researchers found that the theory and
the experiment aligned – except for one important
detail. Researchers previously thought that the atoms
on the surface were arranged in groups of four in
one direction but only one in the other. The new
finding shows that they are in groups of four in
one direction but in groups of three in the other
direction, Smith said. The discrepancy calls into
question the model scientists have accepted for the
last seven years and the understanding of the surface
structure.
The surface of the material is not easy to work
with, Smith noted, because it's sensitive to how
scientists handle it. A different structure could
be created simply by exposing the crystalline surface
to other elements. For example, the accidental contact
of arsenic (an element commonly used in semiconductor
growth) with the crystal surface has affected other
researchers' data in the past.
“The relevance of modeling surfaces is that the
ordering of atoms on a surface can be substantially
different from the one in the bulk of the material,” Sandler
said.
The new research could help scientists learn how
to use cubic gallium nitride as a new semiconductor
for lasers and other electronic devices such as display
technologies and bright blue light-emitting diode
(LED) applications. It also may help them grow layers
of the material more precisely to create technological
applications. But before scientists can make use
of this potentially valuable material, they first
must understand its basic properties so they can
begin tackling its drawbacks, said Smith, director
of Ohio University's Nanoscale and Quantum Phenomena
Institute.
“Cubic gallium nitride is more difficult to grow
[than the popular hexagonal type of gallium nitride
crystal],” said Smith. “But its cubic properties
make it more compatible with other commonly used
materials, and so it has more potential for integration
into mainstream devices.”
The research was supported by grants from the National
Science Foundation and Spain's Ministry of Science
and Technology and its Ministry of Education and
Science.
This project is the first major paper published
by Ohio University's
Nanoscale Interdisciplinary Research Team , a
collaboration of researchers funded by the NSF.
Ohio University Office of Research Communications
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