The Materials Spectrum: Filling a Critical Gap
This week’s new study could open the door to next-generation transparent electronics.
These see-through devices may be embedded in glass, flexible displays, and smart contact lenses. This would bring to life futuristic devices that look like science fiction.
Researchers have searched for a new type of electronic-based semiconducting metal for many decades. This optical transparency could allow these fully-transparent electronics.
These devices, which are based on oxygen, could be used in power electronics or communication technology to reduce the carbon footprint of our utility systems.
RMIT’s team has introduced ultrathin beta tellurite to 2D semiconducting materials. This brings an end to decades-long searches for high-mobility p-type oxygen.
“This new, high-mobility, p-type olefin fills a critical gap in the materials spectrum to allow fast, transparent circuits,” said Dr. Torben Däneke, team leader. He led the collaboration across three FLEET Nodes.
The long-sought-after, oxide-based semiconductors have other vital benefits, including their stability in the air, lower purity requirements, and ease of deposition.
Torben says, “In our advance, the missing link was finding a right, positive approach.”
Positivity was lacking
There are two types of semiconducting materials. The ‘N-type materials are rich in negatively-charged electrons, while the ‘p-type semiconductors have plenty of positively-charged holes.
This stacking of complementary n and p-type material makes electronic devices like diodes, rectifiers, and logic circuits possible.
A molten mixture of tellurium and selenium is rolled on a surface to deposit an atomically thin sheet of beta-tellurite. Credit: FLEET
These materials are essential for modern life, as they are the building blocks of all smartphones and computers.
One of the barriers to using oxide devices is that, while there are many high-performance n-type oxides, there need to be higher-quality p-type oxygens.
Action is prompted by theory.
A 2018 computational study found that beta-tellurite, b-TeO2, could be an attractive candidate for p-type oxide. Tellurium’s unique place in the periodic tables means it can behave as a metal or a non-metal. This gives its oxide unique, valuable properties.
Dr. Torben Dänke, an associate investigator in FLEET, said that “this prediction encouraged our group from RMIT University to investigate its properties and application.”
Liquid metal — a way to explore 2D materials
Dr. Daeneke’s group demonstrated the isolation and synthesis of beta-tellurite using a specially developed synthesis method that relies on liquid metal Chemistry.
Patjaree Aukarasereenont, the co-first author, explains that a molten mixture of selenium and tellurium (Te) is prepared and allowed to roll on a surface.
“The oxygen in the ambient air causes the molten droplet to form a thin oxide layer of beta-tellurite on its surface. This oxide layer forms when the liquid droplet is rolled on the surface and sticks to it, creating atomically thin oxide sheets.
“The process is very similar to drawing. You use a glass rod as a pen, and the liquid metal is your ink,” says Ms. Aukarasereenont. She is currently a FLEET Ph.D. student at RMIT.
The desirable b-phase tellurite can grow below 300 degrees Celsius, but pure tellurium has an extremely high melting point at 500 degrees Celsius. Selenium was used to create an alloy with a lower melting point to make the synthesis possible.
“The ultrathin sheets we have obtained are only 1.5 nanometers thick, corresponding to very few atoms. Dr. Ali Zavabeti, the co-author, explained that the material was transparent in the visible spectrum. It had a bandgap value of 3.7 eV. This means they are virtually invisible to the human eye.
Assessment of beta-tellurite up to 100x faster
Field-effect transistors (FETs) were created to assess the electronic properties of the materials.
These devices displayed characteristic p-type switching and a high hole mobility (roughly 140 cm2V-1s-1), which shows that beta-tellurite can be ten- to one hundred times faster than existing p-type silicon semiconductors. Ms. Patjaree aukarasereenont stated that the material’s excellent on/off ratio (over 106) is suitable for power-efficient and fast devices.
Dr. Ali Zavabeti stated that the findings “close a crucial gap” in the electronic material repository.
“Having a transparent, fast p-type semiconductor available to us can revolutionize transparent electronics while enabling better displays, improved energy-efficient devices, and more efficient use of electricity.”
This team will continue to explore the potential of this new semiconductor. Dr. Torben Däneke says that further research on this material will focus on integration into existing and future-generation consumer electronics.