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Graphene Photodetector Integrated with Semiconductor Chip

Thomas Mueller

Thomas Mueller (H. Lackinger, Vienna University of Technology)

Researchers at Vienna University of Technology and Johannes Kepler University in Linz, Austria built a detector and converter of optical signals with graphene into a traditional semiconductor chip, making it easier to integrate optics and electronics in a single device. The team led by Vienna’s Thomas Mueller published its findings online this week in the journal Nature Photonics (paid subscription required).

Signals transmitted with photons over optical fibers need to be converted to electrons to be processed with complementary metal–oxide semiconductor (CMOS) chips, the standard electronic device. Previous attempts at converting optical signals on silicon chips use the material germanium, which succeed in detecting the signals, but only in a limited range of light wave frequencies.

Mueller and colleagues in 2010 showed the potential of graphene for detection of optical signals. Graphene is closely related to graphite like that used in pencils, but consists of only a single atomic layer of carbon atoms. The material is very light, strong, chemically stable, and can conduct both heat and electricity, with applications in fields such as electronics, energy, and health care.

In the new study, the Vienna-Kepler team built a device that moves that potential closer to commercial applications. In their paper, the researchers report demonstrating detection of optical signals across a spectrum range encompassing all of the fiber-optic telecommunication bands. Mueller says their device funnels the optical signal through a narrow waveguide, no more than 500 nanometers in diameter (1 nanometer equals 1 billionth of a meter). The waveguide directs the signal to a layer of graphene that converts it into electronic data for processing on the chip.

The researchers say the graphene photodetector works fast, achieving multi-gigahertz speeds. The detector is also compact; some 20,000 detectors can fit on a single chip one square centimeter in size.

Optical transmissions are becoming important for transferring data within as well as between computers. “When large computer clusters work with many processor cores at the same time, a lot of information has to be transferred between the cores,” notes Mueller in a university statement. “As graphene allows switching between optical and electrical signals very quickly, this data can be exchanged optically. This speeds up the data exchange and requires much less electrical energy.”

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