Transistors for next-gen green electronics

Researchers at UC Santa Barbara, in collaboration with the University of Notre Dame, have recently demonstrated the highest reported drive current on a transistor made of a monolayer of tungsten diselenide (WSe2), a 2-dimensional atomic crystal categorised as a transition metal dichalcogenide (TMD).

The discovery is also said to be the first demonstration of an ‘n-type’ WSe2 field-effect-transistor (FET), showing the tremendous potential of this material for future low-power and high-performance integrated circuits.

“There is growing worldwide interest in these 2D crystals due to the many possibilities they hold for the next generation of integrated electronics, optoelectronics and sensors,” commented Professor Pulickel Ajayan, the Anderson Professor of Engineering at Rice University and an authority on nanomaterials.

Monolayer WSe2 is similar to graphene in that it has a hexagonal atomic structure and derives from its layered bulk form in which adjacent layers are held together by relatively weak Van der Waals forces. However, WSe2 has a key advantage over graphene.

“In addition to its atomically smooth surfaces, it has a considerable band gap of 1.6 eV,” explained Kaustav Banerjee, professor of electrical and computer engineering and director of the Nanoelectronics Research Lab at UCSB.

“Understanding the nature of the metal-TMD interfaces was key to our successful transistor design and demonstration,” explained Banerjee. Banerjee’s group pioneered a methodology using ab-initio density functional theory (DFT) that established the key criteria needed to evaluate such interfaces leading to the best possible contacts to the monolayer TMDs.

“DFT simulations provide critical insights to the various factors that effectively determine the quality of the interfaces to these 2D materials, which is necessary for achieving low contact resistances,” added Jiahao Kang, a PhD student in Banerjee’s group and co-author of the study.

Banerjee’s research team also includes UCSB researchers Wei Liu, Jiahao Kang, Deblina Sarkar, Yasin Khatami and Professor Debdeep Jena of Notre Dame. Their study was published in the May 2013 issue of Nano Letters. The research was supported by the National Science Foundation, the California NanoSystems Institute at UC Santa Barbara and the Materials Research Laboratory at UCSB: an NSF MRSEC.