Apr 05, 2021 |
A new, positive approach could be the key to next-generation, transparent electronics
(Nanowerk News) A new study (Nature Electronics, "High mobility p-type semiconducting two-dimensional β-TeO2"), out this week, could pave the way to revolutionary, transparent electronics.
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Such see-through devices could potentially be integrated in glass, in flexible displays and in smart contact lenses, bringing to life futuristic devices that seem like the product of science fiction.
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For several decades, researchers have sought a new class of electronics based on semiconducting oxides, whose optical transparency could enable these fully-transparent electronics.
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Oxide-based devices could also find use in power electronics and communication technology, reducing the carbon footprint of our utility networks.
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A RMIT-led team has now introduced ultrathin beta-tellurite to the two-dimensional (2D) semiconducting material family, providing an answer to this decades-long search for a high mobility p-type oxide.
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“This new, high-mobility p-type oxide fills a crucial gap in the materials spectrum to enable fast, transparent circuits,” says team leader Dr Torben Daeneke, who led the collaboration across three FLEET nodes.
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Other key advantages of the long-sought-after oxide-based semiconductors are their stability in air, less-stringent purity requirements, low costs and easy deposition.
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“In our advance, the missing link was finding the right, ‘positive’ approach,” says Torben.
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Positivity has been lacking
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There are two types of semiconducting materials. ‘N-type’ materials have abundant negatively-charged electrons, while ‘p-type’ semiconductors possess plenty of positively-charged holes.
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It’s the stacking together of complementary n-type and p-type materials that allows electronic devices such as diodes, rectifiers and logic circuits.
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Modern life is critically reliant on these materials since they are the building blocks of every computer and smartphone.
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A barrier to oxide devices has been that while many high-performance n-type oxides are known, there is a significant lack of high-quality p-type oxides.
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Theory prompts action
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However in 2018 a computational study revealed that beta-tellurite (β-TeO2) could be an attractive p-type oxide candidate, with tellurium’s peculiar place in the periodic table meaning it can behave as both a metal and a non-metal, providing its oxide with uniquely useful properties.
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“This prediction encouraged our group at RMIT University to explore its properties and applications,” says Dr Torben Daeneke, who is a FLEET associate investigator.
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Liquid metal – pathway to explore 2D materials
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Dr Daeneke’s team demonstrated the isolation of beta-tellurite with a specifically developed synthesis technique that relies on liquid metal chemistry.
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“A molten mixture of tellurium (Te) and selenium (Se) is prepared and allowed to roll over a surface,” explains co-first author Patjaree Aukarasereenont.
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“Thanks to the oxygen in ambient air, the molten droplet naturally forms a thin surface oxide layer of beta-tellurite. As the liquid droplet is rolled over the surface, this oxide layer sticks to it, depositing atomically thin oxide sheets in its way.”
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“The process is similar to drawing: you use a glass rod as a pen and the liquid metal is your ink,” explains Ms Aukarasereenont, who is a FLEET PhD student at RMIT.
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While the desirable β-phase of tellurite grows below 300 °C, pure tellurium has a high melting point, above 500 °C. Therefore, selenium was added to design an alloy that has a lower melting point, making the synthesis possible.
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“The ultrathin sheets we obtained are just 1.5 nanometres thick - corresponding to only few atoms. The material was highly transparent across the visible spectrum, having a bandgap of 3.7 eV which means that they are essentially invisible to the human eye” explains co-author Dr Ali Zavabeti.
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Assessing beta-tellurite: up to 100 times faster
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To assess the electronic properties of the developed materials, field-effect transistors (FETs) were fabricated.
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“These devices showed characteristic p-type switching as well as a high hole mobility (roughly 140 cm2V-1s-1), showing that beta-tellurite is ten to one hundred times faster than existing p-type oxide semiconductors. The excellent on/off ratio (over 106) also attests the material is suitable for power efficient, fast devices” Ms Patjaree Aukarasereenont said.
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“The findings close a crucial gap in the electronic material library,” Dr Ali Zavabeti said.
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“Having a fast, transparent p-type semiconductor at our disposal has the potential to revolutionise transparent electronics, while also enabling better displays and improved energy-efficient devices.”
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The team plans to further explore the potential of this novel semiconductor. “Our further investigations of this exciting material will explore integration in existing and next-generation consumer electronics,” says Dr Torben Daeneke.
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