Researchers from the University of Washington have reported on a light emitting diode (LED) made form tungsten diselenide (WSe2) that is just three atomic layers thick. The research team claims that this is the thinnest LED that can be used as a source of optical energy in electronics.
Tungsten diselenide is one of a group of elements and compounds that naturally form a two-dimensional sheet. The containment of the electron flow in two-dimensions introduces quantum mechanical effects and makes them behave somewhat differently to materials in bulk. It also means that minimal amounts of material can be used or the material can be stacked as a design option.
The University of Washington led an international team that was able to make lateral p–n junctions in monolayer WSe2 induced electrostatically. The WSe2 material was supported on an insulating dielectric of boron nitride with multiple metal gates beneath. This structure allowed the injection of electrons and holes, and, combined with the high optical quality of WSe2, produced an electroluminescence with 1,000 times smaller injection current and 10 times smaller line width than in molybdenum disulphide (MoS2). According to the abstract of the Nature paper this system has the required ingredients for new types of optoelectronic device, such as spin- and valley-polarized light-emitting diodes, on-chip lasers and two-dimensional electro-optic modulators.
"We are able to make the thinnest-possible LEDs, only three atoms thick yet mechanically strong. Such thin and foldable LEDs are critical for future portable and integrated electronic devices," said Xiaodong Xu, a UW assistant professor in materials science, engineering and physics, in a statement.
Xu and Jason Ross, a UW materials science and engineering graduate student, co-authored a paper about this technology that appeared online March 9 in Nature Nanotechnology. The reported LEDs are 10 to 20 times thinner than conventional LEDs but the light output can be seen by standard measuring equipment, said Ross.
The research team made sheets of tungsten diselenide and then used adhesive tape to extract a single sheet of this material from thick, layered pieces. This method was originally used to isolate monolayers of graphene, by Professors Andre Geim and Konstantin Novoselov at the University of Manchester.
One possibility opened up by the ability to make LEDs on the atomic scale is that of using light rather than electrons as interconnect signaling. Photonic data transmission across a die would be energy efficient
The research team is working on more efficient ways to create these thin LEDs and looking at what happens when two-dimensional materials are stacked in different ways. Additionally, these materials have been shown to react with polarized light in new ways that no other materials can, and researchers also will continue to pursue those applications.
"A promising solution is to replace the electrical interconnect with optical ones, which will maintain the high bandwidth but consume less energy," said Professor Xu. "Our work makes it possible to make highly integrated and energy-efficient devices in areas such as lighting, optical communication and nano lasers."
Co-authors on the paper include: Aaron Jones and David Cobden of the UW; Philip Klement of Justus Liebig University in Germany; Nirmal Ghimire, Jiaqiang Yan and D.G. Mandrus of the University of Tennessee and Oak Ridge National Laboratory; Takashi Taniguchi, Kenji Watanabe and Kenji Kitamura of the National Institute for Materials Science in Japan; and Wang Yao of the University of Hong Kong.
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