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The research team of Assistant Professor Tingyi Gu includes (from left to right) graduate student Dun Mao, PhD student Thomas Kananen and postdoctoral fellow Tiantian Li. Credit: University of Delaware
If you use a smartphone, a laptop or a tablet, you benefit from research in photonics, the study of light. At the University of Delaware, a team led by Tingyi Gu, an assistant professor in electrical and computer engineering, develops state-of-the-art technology for photonic devices that could enable faster communications between devices and, hence, people who use them.
The research group recently developed a silicon-graphene device capable of transmitting radio frequency waves in less than a picosecond with a bandwidth less than terahertz, which is a wealth of information, fast. Their work is described in a new article published in the journal Applied electronic materials ACS.
"In this work, we explored the bandwidth limitation of graphene-integrated silicon photonics for future optoelectronic applications," said Dun Mao, graduate student, first author of the article.
Silicon is an abundant natural material commonly used as a semiconductor in electronic devices. However, researchers have exhausted the potential of devices with only silicon semiconductors. These devices are limited by the mobility of silicon media, the rate at which a charge travels through the material, and the indirect band gap, which limits its ability to release and absorb light.
The Gu team now combines silicon with a more favorable material, graphene, a 2D material. Two-dimensional materials get their name from the simple layer of atoms. Compared with silicon, graphene has better carrier mobility and a direct forbidden band, allows faster electronic transmission and better electrical and optical properties. By combining silicon and graphene, scientists could continue to use technologies already used with silicon devices. They would simply work faster with the silicon-graphene combination.
A team from the University of Delaware has developed a silicon-graphene device capable of transmitting radio frequency waves in less than a picosecond at a bandwidth less than terahertz. Credit: University of Delaware
"Looking at the properties of materials, can we do more than what we are working with? That's what we want to understand," said PhD student Thomas Kananen.
To combine silicon with graphene, the team used a method developed and described in an article published in 2018 in npj 2-D Materials and Application. The team placed graphene in a special place called p-i-n junction, interface between materials. By placing the graphene at the p-i-n junction, the team optimized the structure so as to improve the responsiveness and speed of the device.
This method is robust and could easily be applied by other researchers. This process takes place on a 12-inch wafer of thin material and uses components of less than one millimeter. Some components were manufactured in a commercial smelter. Other work took place at the UD Nanofabrication Factory, led by Matt Doty, Associate Professor in Materials Science and Engineering.
"The UDN Nanofabrication Facility (UDNF) is a staff-assisted facility that allows users to fabricate devices in lengths as small as 7 nm, which is about 10,000 times smaller than the diameter of the device. a human hair, "said Doty. "The UDNF, which opened in 2016, has brought new avenues of research in areas ranging from optoelectronics to biomedicine to plant science."
If you use a smartphone, a laptop or a tablet, you benefit from research in photonics, the study of light. The research focused on device fabrication at the UD nanofabrication facility. Credit: University of Delaware
The combination of silicon and graphene can be used as a photodetector, which detects light and produces current, with more bandwidth and a shorter response time than current offerings. All of this research could lead to cheaper and faster wireless devices in the future. "This can make the network stronger, better and cheaper," said Tiantian Li, postdoctoral associate and first author of the article on 2-D materials and applications from NPJ. "It's a key point of photonics."
The team is now thinking of ways to expand the applications of this material. "We are looking at more components based on a similar structure," Gu said.
Explore further:
The spectacular performance of graphene in high-speed optical communications
More information:
Dun Mao et al. Bandwidth limit of graphene-silicon optoelectronics directly in contact, Applied electronic materials ACS (2019). DOI: 10.1021 / acsaelm.8b00015
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