Graphene-based photodetectors can efficiently convert infrared light into electrical signals, three independent studies report this week.
Figure 1: The light signal arrives through a waveguide
The work "makes it very likely that graphene will soon replace germanium and compound semiconductors in high-performance light detectors," said editors at Nature Photonics, which published all three papers.
Graphene — a single layer of carbon atoms arranged in a honeycomb lattice — with its exceptional electrical and optical properties, is being pursued as a more attractive alternative to germanium or compound semiconductors for silicon-based photonics. Attempts to integrate photodetectors made of materials such as germanium onto a chip have resulted in bandgap-limited detectors that can process light of only a specific wavelength range. But graphene — a zero-bandgap material — has been shown to convert all wavelengths used in telecommunications equally well, and recent graphene integration work has yielded high-performance optoelectronic devices such as modulators, polarizers and photodetectors.
Figure 1: The light signal arrives through a waveguide (left), in the 2-µm-wide graphene sheet, electrical current is generated. Courtesy of TU Vienna.
All three of the new papers appear this week. Dirk Englund and colleagues from Columbia University, MIT and the IBM T.J. Watson Research Center report an ultrafast graphene light detector with a responsivity about 16 times greater than that of previous graphene-based detectors over a broad bandwidth of 1.45 to 1.59 µm. Although that amount of current still lags behind germanium photodetectors, “The gap is closing very, very quickly,” Englund told Nature.
Thomas Müller and co-workers at Vienna University of Technology, working with teammates from the Johannes Kepler University in Linz, describe a graphene light detector with multigigahertz operation for a wide range (1.31 to 1.65 µm) that includes all the bands used by optical fiber communication systems. Its responsivity is about eight times higher than that of earlier graphene light detectors.
Xiaomu Wang and colleagues at The Chinese University of Hong Kong report on fabricating a high-responsivity graphene photodiode that operates at mid-infrared frequencies, with potential applications in environmental monitoring and on-chip infrared spectroscopy for medical testing.
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