2023-07-31 22:10:00
In the area of emerging technologies, a team of researchers has discovered a potential solution to a major problem that has been holding back the development of high-quality 2D semiconductors. These are essential for next-generation electronics, encompassing artificial intelligence and the Internet of Things (IoT).
The tungsten diselenidea semiconductor, has been shown to be a potential material for nanosheet transistors, electronic devices that harness layers of atomically thin material to control and manipulate the flow of electric current.
This research has taken on increased importance since last year’s passage of the CHIPS and Science Act, aimed at bolstering US efforts to relocate production and development of semiconductor technology.
Nevertheless, synthesizing a monolayer sheet of tungsten diselenide, which is only three atoms thick, on sapphire wafer areas ranging from 8 to 12 inches in diameter, proved to be a challenge.
The Challenges of Tungsten Diselenide Synthesis
The difficulty lies in a defect in the material known as “twin mirrors“. These mirror twin borders form from oppositely oriented diselenide tungsten crystals on the sapphire pancakes. This defect scatters electrons as they pass through the 2D layer, reducing the performance of the nanosheet transistor.
In the study published in Nature Nanotechnology, researchers from the 2DCC-MIP (Two-Dimensional Crystal Consortium – Materials Innovation Platform) supported by the National Science Foundation used the metalorganic chemical vapor deposition (MOCVD)a technology that allows ultra-thin monocrystalline layers to be deposited on a substrate, in this case a sapphire wafer.
2DCC-MIP researchers pioneered the use of this technique for the synthesis of transition metal dichalcogenides at the wafer scale, such as tungsten diselenide.
Significant discoveries in the structuring of crystals
The researchers found that by controlling the conditions of the MOCVD process, most crystals could be induced to attach to the sapphire stages. During the experiments, they made a bonus discovery: if the crystals attach at the top of the stage, they align in one crystallographic direction, if they attach at the bottom, they align in the opposite direction.
“If the crystals can all be aligned in the same direction, then the mirror twin defects in the layer will be reduced or even eliminated”said Joan Redwing, director of 2DCC-MIP.
Confirmation of the theory and future impact
The 2DCC-MIP researchers collaborated with Krystal York, a PhD student from Western Michigan University, to confirm this theory. His experiments helped confirm that this method was indeed effective.
“This experimental observation provided a verification of the theoretical model that was developed to explain the place of attachment of the tungsten diselenide crystals on the steps on the sapphire wafer”Redwing said.
Wafer-scale tungsten diselenide samples on sapphire, produced using this new MOCVD process, are now available to researchers outside of Penn State via the 2DCC-MIP user program.
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This work is critically important as semiconductor chips need to advance to meet the demands of a new world of electronics looming on the horizon. Applications like artificial intelligence and the Internet of Things will require performance improvements as well as ways to reduce the power consumption of electronic devices.
“Applications such as artificial intelligence and the Internet of Things will require further performance improvements as well as ways to reduce the power consumption of electronics“, a conclu M. Redwing. “High-quality 2D semiconductors made from tungsten diselenide and related materials are important materials that will play a role in next-generation electronics.“
Atomic-scale steps on sapphire substrates align crystals of 2D materials, reduce defects, and improve performance of electronic devices. Credit: Jennifer M. McCann
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