Skip to main content

2D FET from polymorphic material molbdenum telluride


In simple terms, FETs can be thought as high-speed switches, composed of two metal electrodes and a semiconducting channel in between. Electrons (or holes) move from the source electrode to the drain electrode, flowing through the channel. While 3D FETs have been scaled down to nanoscale dimensions successfully, their physical limitations are starting to emerge. Short semiconductor channel lengths lead to a decrease in performance: some electrons (or holes) are able to flow between the electrodes even when they should not, causing heat and efficiency reduction. To overcome this performance degradation, transistor channels have to be made with nanometer-scale thin materials. However, even thin 3D materials are not good enough, as unpaired electrons, part of the so-called "dangling bonds" at the surface interfere with the flowing electrons, leading to scattering.
Passing from thin 3D FETs to 2D FETs can overcome these problems and bring in new attractive properties. "FETs made from 2D semiconductors are free from short-channel effects because all electrons are confined in naturally atomically thin channels, free of dangling bonds at the surface," explains Ji Ho Sung, first author of the study. Moreover, single- and few-layer form of layered 2D materials have a wide range of electrical and tunable optical properties, atomic-scale thickness, mechanical flexibility and large bandgaps (1~2 eV).
The major issue for 2D FET transistors is the existence of a large contact resistance at the interface between the 2D semiconductor and any bulk metal. To address this, the team devised a new technique to produce 2D transistors with semiconductor and metal made of the same chemical compound, molybdenum telluride (MoTe2). It is a polymorphic material, meaning that it can be used both as metal and as semiconductor. Contact resistance at the interface between the semiconductor and metallic MoTe2 is shown to be very low. Barrier height was lowered by a factor of 7, from 150meV to 22meV.
IBS scientists used the chemical vapor deposition (CVD) technique to build high quality metallic or semiconducting MoTe2 crystals. The polymorphism is controlled by the temperature inside a hot-walled quartz-tube furnace filled with NaCl vapor: 710°C to obtain metal and 670°C for a semiconductor.
The scientists also manufactured larger scale structures using stripes of tungsten diselenide (WSe2) alternated with tungsten ditelluride (WTe2). They first created a thin layer of semiconducting WSe2 with chemical vapor deposition, then scraped out some stripes and grew metallic WTe2 on its place.
It is anticipated that in the future, it would be possible to realize an even smaller contact resistance, reaching the theoretical quantum limit, which is regarded as a major issue in the study of 2D materials, including graphene and other transition metal dichalcogenide materials.

Journal Reference
Ji Ho Sung, Hoseok Heo, Saerom Si, Yong Hyeon Kim, Hyeong Rae Noh, Kyung Song, Juho Kim, Chang-Soo Lee, Seung-Young Seo, Dong-Hwi Kim, Hyoung Kug Kim, Han Woong Yeom, Tae-Hwan Kim, Si-Young Choi, Jun Sung Kim, Moon-Ho Jo. Coplanar semiconductor–metal circuitry defined on few-layer MoTe2 via polymorphic heteroepitaxy. Nature Nanotechnology, 2017; DOI: 10.1038/NNANO.2017.161
Labels:

Comments

Post a Comment

Popular posts from this blog

Nano thin film Barium Stannate :New revolution to electronics and solar industry

A team of researchers, led by the University of Minnesota, have discovered a new nano-scale thin film material with the highest-ever conductivity in its class. The new material could lead to smaller, faster, and more powerful electronics, as well as more efficient solar cells. The discovery is being published today in  Nature Communications , an open access journal that publishes high-quality research from all areas of the natural sciences. Researchers say that what makes this new material so unique is that it has a high conductivity, which helps electronics conduct more electricity and become more powerful. But the material also has a wide bandgap, which means light can easily pass through the material making it optically transparent. In most cases, materials with wide bandgap, usually have either low conductivity or poor transparency. "The high conductivity and wide bandgap make this an ideal material for making optically transparent conducting films which could be used...
Post a Comment
Read more

Transition metal dichalcogenides (TMDs): a new revolution to quantum technologies

Transition metal dichalcogenides (TMDs) are layered semiconductors that can be exfoliated into layers only a few atoms thick. Recent research has shown that some TMDs can contain quantum light sources that can emit single photons of light. Until now, the occurrence of these quantum light emitters has been random. Now, researchers in the Graphene Flagship working at the University of Cambridge, UK, have created large scale arrays of these quantum emitters in different TMD materials. The work, also involving researchers from Harvard University, US, is published in  Nature Communications . This new approach leads to large quantities of on-demand, single photon emitters, paving the way for integrating ultra-thin, single photons in electronic devices. Quantum light emitters, or quantum dots, are of interest for many different applications, including quantum communication and networks. Until now, it has been very difficult to produce large arrays of quantum emitters close together w...
Post a Comment
Read more

Nano Thermal Mechanical Rectification : A New way to harness heat to power computer

One of the biggest problems with computers, dating to the invention of the first one, has been finding ways to keep them cool so that they don't overheat or shut down . Instead of combating the heat, two University of Nebraska-Lincoln engineers have embraced it as an alternative energy source that would allow computing at ultra-high temperatures. Sidy Ndao, assistant professor of mechanical and materials engineering, said his research group's development of a nano-thermal-mechanical device, or thermal diode, came after flipping around the question of how to better cool computers. "If you think about it, whatever you do with electricity you should (also) be able to do with heat, because they are similar in many ways," Ndao said. "In principle, they are both energy carriers. If you could control heat, you could use it to do computing and avoid the problem of overheating." A paper Ndao co-authored with Mahmoud Elzouka, a graduate student in mechanica...
Post a Comment
Read more