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Narayan Discovers New Class of More Efficient Transparent Conductors

September 28th, 2012

The transparent conductors are critical to efficiency of light emitting diodes for solid-state lighting, organic solar cells and host of display devices. Achieving high electrical conductivity and high transparency in the same materials system has presented a fundamental challenge to materials scientists over the years, as these two properties go in the opposite directions. In other words, we want a transparent material like glass (having wide bandgap) which also has a high electrical conductivity typical of opaque metal with zero bandgap. Tin doped indium oxide or indium tin oxide (ITO) has served us well over the years as a transparent conductor. However, ITO has the element of indium whose supply is dwindling rapidly. As the world is running out of indium sources, we need new transparent conductors from elements, which are more abundant in the earth's crust.

Professor Jagdish (Jay) Narayan, Inaugural MRS Fellow, has discovered and patented (US Patent # 8,222,740 (July 17, 2012)) a new class of zinc oxide based transparent conductors, which are alloyed with optimum concentrations of Ga and Al elements. These alloys have electrical and optical properties comparable to more expensive indium tin oxide (ITO). The work function of zinc oxide based alloys can be enhanced by a couple of monolayers of molybdenum oxide (MoOx) and nickel oxide (NiOx), making zinc oxide based composites superior to ITO for contacting and electroding gallium nitride based light emitting diodes (GaN based LEDs) for solid-state lighting and other devices like organic solar cells. In addition, zinc oxide based materials are more stable and exhibit superior diffusion barrier characteristics compared to ITO contacts. Thus, ZnO based contacts of this invention enhance optical power and reduce voltage and are more stable and less expensive, compared to current ITO based contacts, needed for next-generation high-efficiency LEDs for solid-state lighting, organic solar cells and a variety of display devices. The solid-state bulbs have a potential to convert electricity into light with almost 100% efficiency. The incandescent bulbs, on the other hand, convert less than 5% of electrical energy into light and the rest is wasted as heat. This patent is being licensed by major GaN LED manufacturers. This research has been published in a series of papers in the Journal of Applied Physics and the Applied Physics Letters, and it was funded by the National Science Foundation.

Professor Narayan is the John Fan Family Distinguished Chair Professor in the Department of Materials Science and Engineering, and also has appointment as Distinguished Visiting Scientist at Oak Ridge National Laboratory. After graduating with distinction and first rank from India's top institution (IIT, Kanpur) in 1969, Narayan continued his studies at the UC, Berkeley, and obtained his MS (1970) and PhD (1971) degrees in a record time of two years.

Narayan worked as Research Metallurgist at Lawrence Berkeley National Laboratory (1971-72) and Senior Scientist and Group Leader at Oak Ridge National Lab (1972-83), before joining North Carolina State University in 1983 as senior professor and Director of Microelectronics Center of North Carolina. He also served as Director of Division of Materials Research (1990-92) of the National Science Foundation.

Professor Narayan has been recognized worldwide with many honors and awards, including the Triple Crown- Acta Materialia Gold Medal, ASM Gold Medal and TMS R. F. Mehl Gold Medal- in the field of materials science and engineering. This record of gold medals follows legendary Professor Morris Cohen of MIT and Sir Alan Cottrell of Cambridge University. Professor Narayan's other honors include: 2012 Holladay Medal (highest NCSU honor), 2011 RJ Reynolds Award, 2011 Lee Hsun Lecture Award from the Chinese Academy of Sciences, 2011 MRS Forum and 2011 MS&T International Conference in Narayan's honor, Edward DeMille Campbell Lecture and Prize, US-DOE Outstanding Research Award, three IR-100 Awards, NSF Distinguished Service Award, and IIT/K Distinguished Alumnus Award. He has been honored by eight professional societies, including Inaugural MRS Fellow, Life Member and Fellow of TMS, Life Member and Fellow of APS, ASM Fellow, AAAS Fellow, Honorary Member MRS-I, Fellow Bohmische Physical Society, and Life Member and Fellow of National Academy of Sciences (India). Professor Narayan has published over 500 papers in archival journals and received 40 patents which have over 17,400 citations and h-index approaching 70 with 32 citation classics (Google Scholar).

North Carolina State University