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  • New Bandgap Boundaries Could Boost Electronics
Feb 2012
OAK RIDGE, Tenn., Feb. 23, 2012 — A novel layer-by-layer growth technique can achieve a 30 percent reduction in the bandgap of complex metal oxides, bumping up the performance of solar cells, LEDs, displays and other electronic devices.

While complex transition metal oxides have for years held promise for a variety of information and energy applications, the challenge has been to devise a method to reduce bandgaps of those insulators without compromising the material’s useful physical properties.

The bandgap, a major factor in determining electrical conductivity in a material, directly determines the upper wavelength limit of light absorption. Achieving wide bandgap tunability is highly desirable for developing optoelectronic devices and energy materials.

ORNL’s materials scientists developed a synthesis strategy for discovering novel complex oxide thin films for stronger solar light absorption. (Image: ORNL)

Ho Nyung Lee of Oak Ridge National Laboratory developed the layer-by-layer growth technique. For his achievement, Lee received the Presidential Early Career Award for Scientists and Engineers. Then he and his colleagues used the method to achieve a 30 percent reduction in the bandgap of complex metal oxides, surpassing previous accomplishments of 6 percent — or 0.2 eV — and opening the door to new approaches to controlling bandgap in complex oxide materials.

“Our approach to tuning bandgaps is based on atomic-scale growth control of complex oxide materials, yielding novel artificial materials that do not exist in nature,” Lee said. “This ‘epitaxy’ technique can be used to design entirely new materials or to specifically modify the composition of thin-film crystals with subnanometer accuracy.”

With this discovery, the potential exists for oxides with bandgaps to be continuously controlled over 1 eV by site-specific alloying developed by the ORNL team.

“This work exemplifies how basic research can provide technical breakthroughs that will result in vastly improved energy technologies,” said Michelle Buchanan, associate lab director for ORNL’s Physical Sciences Directorate.

A patent is pending for this technology.

The research was funded initially by the Laboratory Directed Research and Development program and later by the Department of Energy’s Office of Science. Optical measurements were performed in part at the Center for Nanophase Materials Sciences, a DOE-BES user facility at ORNL.

The findings were outlined in Nature Communications.

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In a semiconductor material, the minimum energy necessary for an electron to transfer from the valence band into the conduction band, where it moves more freely.
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