ATHENS, Ohio — For almost a decade, scientists thought theyunderstood the surface structure of cubic gallium nitride, a promisingnew crystalline semiconductor. Research by an interdisciplinary team ofnanoscientists from Ohio University and the Universitat Auṭnoma deBarcelona, however, turns that idea on its head.
Their studypublished in the Sept. 30 online issue of the journal Physical ReviewLetters provides a fresh – and they argue, more accurate – look at thesurface structure of the crystalline material, which could be used inlasers and other electronic devices.
Nancy Sandler, an assistantprofessor of physics and astronomy at Ohio University, and PabloOrdejón, a Barcelona professor specializing in the algorithm used inthe project, calculated several properties using the currently acceptedmodel 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, recentlyhad used scanning tunneling microscopy to capture an image of thesurface.
When they compared the model image with the experimentalimage, the researchers found that the theory and the experiment aligned– except for one important detail. Researchers previously thought thatthe atoms on the surface were arranged in groups of four in onedirection but only one in the other. The new finding shows that theyare in groups of four in one direction but in groups of three in theother direction, Smith said. The discrepancy calls into question themodel scientists have accepted for the last seven years and theunderstanding of the surface structure.
The surface of thematerial is not easy to work with, Smith noted, because it’s sensitiveto how scientists handle it. A different structure could be createdsimply by exposing the crystalline surface to other elements. Forexample, the accidental contact of arsenic (an element commonly used insemiconductor growth) with the crystal surface has affected otherresearchers’ data in the past.
“The relevance of modelingsurfaces is that the ordering of atoms on a surface can besubstantially different from the one in the bulk of the material,”Sandler said.
The new research could help scientists learn how touse cubic gallium nitride as a new semiconductor for lasers and otherelectronic devices such as display technologies and bright bluelight-emitting diode (LED) applications. It also may help them growlayers of the material more precisely to create technologicalapplications. But before scientists can make use of this potentiallyvaluable material, they first must understand its basic properties sothey can begin tackling its drawbacks, said Smith, director of OhioUniversity’s Nanoscale and Quantum Phenomena Institute.
“Cubicgallium nitride is more difficult to grow [than the popular hexagonaltype of gallium nitride crystal],” said Smith. “But its cubicproperties make it more compatible with other commonly used materials,and so it has more potential for integration into mainstream devices.”
Theresearch was supported by grants from the National Science Foundationand Spain’s Ministry of Science and Technology and its Ministry ofEducation and Science.
This project is the first major paperpublished by Ohio University’s Nanoscale Interdisciplinary ResearchTeam, a collaboration of researchers funded by the NSF.
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