Researchers at the University of Washington (UW) have demonstrated electroluminescence in a flexible, mechanically strong construct of the semiconductor tungsten selenide only three atoms thick.
The researchers harvested single sheets of tungsten selenide (WSe2) using adhesive tape, a technique invented for the production of graphene. They used a support and dielectric layer of boron nitride on a base of silicon dioxide on silicon, to come up with the thinnest possible LED.
Diagram showing the layers of the almost two-dimensional LED.
The LEDs now used in most consumer electronics are rigid and are hundreds to thousands of times as thick as the material being developed at UW -- which the team characterizes as 1/10,000th the thickness of a human hair.
Existing inorganic LEDs are not appropriate for use in bendable, foldable applications such as electronic devices and displays integrated into clothing. Organic light-emitting diodes are the usual candidates for such applications, but the techniques being pioneered at UW can produce devices that are not only much thinner -- and stackable -- but also far more versatile.
"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," the team writes in the March 9 issue of Nature Nanotechnology (subscription required). "Our work makes it possible to make highly integrated and energy-efficient devices in areas such as lighting, optical communication, and nano lasers," UW said in a press release.
It is not clear whether this early research will lead to processes usable in applications such as general or automotive lighting, where high-power devices based on gallium nitride are established and rapidly evolving according to Haitz's Law, the solid-state lighting equivalent of Moore's Law. But the possibilities the research opens up for rapid, energy-efficient optical communications at the nano scale are tantalizing.
The Nature Nanotechnology article is behind a paywall, but the research team has posted a preprint on the arXiv site.
Other teams at work
Teams from MIT and the Vienna University of Technology also published work on WSe2 in the same issue of Nature Nanotechnology. The MIT researchers concentrated on the LED potential of the material, as UW did, while Vienna explored using WSe2 in photovoltaic applications. The material is transparent, leading to speculation about solar cells embedded in window glass.
— Keith Dawson , Editor-in-Chief, All LED Lighting