Super ‘superlattices’ could enable ‘superfast’ transistors

Research led by UCLA has developed a method to make new kinds of artificial superlattices – also known as 2D materials. The team says that, while current superlattices feature alternating layers with similar atomic structures and electronic properties, its superlattice can have different structures, properties and functions.

Such superlattices are believed to hold the prospect of enabling improved and new classes of electronic and optoelectronic devices, with applications including ‘superfast and ultra-efficient semiconductors’ for transistors. According to the team, while one layer of its superlattice could allow a fast flow of electrons, another layer could act as an insulator. This design would confine the electronic and optical properties to single active layers, avoiding interference with other insulating layers. The manufacturing process is also said to be faster and more efficient, with the potential to create superlattices with create thousands of alternating layers – something which is said to be not possible with other approaches. “Traditional semiconductor superlattices can usually only be made from materials with highly similar lattice symmetry, normally with rather similar electronic structures,” said Professor Yu Huang. “For the first time, we have created stable superlattice structures with radically different layers, yet nearly perfect atomic-molecular arrangements within each layer. This new class of superlattice structures has tailorable electronic properties for potential technological applications and further scientific studies.” The UCLA team used electrochemical intercalation to create its superlattice. This technique sees electrons injected into the 2D material, which then attract positively charged ammonium molecules into the spaces between the atomic layers. Ammonium molecules assemble into new layers, creating the superlattice. The researchers first demonstrated their technique using black phosphorus as a base 2D material. The team then inserted ammonium molecules with various sizes and symmetries into a series of 2D materials to create a broad class of superlattices. The structures of the resulting superlattices could then be tailored to provide a range of electronic and optical properties. “The resulting materials could be useful for making faster transistors that consume less power, or for creating efficient light-emitting devices,” Professor Xiangfeng Duan noted. Collaborating in the research were scientists from Caltech, Hunan University, University of Science and Technology of China and King Saud University.

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