By Josh Perry, Editor
[email protected]

Researchers from Yale University (New Haven, Conn.) and the Institute of Photonic Sciences (ICFO) in Barcelona, Spain have developed a new device that uses graphene to detect mid-infrared light (between 8-14 micrometers) and converts it into electrical signals at room temperature.

Illustration of the graphene mid-infrared detector. (Yale University)

According to a report from Yale, this could be a breakthrough for new, enhanced communications systems and thermal imaging devices because, while mid-infrared radiation has already shown its potential in these application, standard room-temperature detectors are very slow.

“The device demonstrated in this study takes advantage of the unique properties of the highly conductive, atomically thin graphene, which is a single layer of carbon atoms, and its plasmon - a quantum of its collective electron oscillations,” the article explained.

Graphene converts the mid-infrared light into plasmons, which then convert into heat. Unlike other materials, graphene works much quicker because its electron temperature rise from plasmon decay is higher.

“Graphene’s resistance is very insensitive to temperature at room temperature, as a result, it’s difficult to electrically detect mid-infrared light except at extremely cold temperatures, which means it can’t be integrated into usable devices,” the article continued. “To that end, in this work the researchers developed a new device that features graphene disk plasmonic resonators connected by quasi-one-dimensional nanoribbons. It can effectively detect the mid-infrared light at room temperature.”

Standard thermal sensors take milliseconds to heat up, but the graphene detector needed only one nanosecond. Researchers believe this makes the device effective for high-speed, free-space communications applications.

The research was recently published in Nature Materials. The abstract stated:

“Optical excitation and subsequent decay of graphene plasmons can produce a significant increase in charge-carrier temperature. An efficient method to convert this temperature elevation into electrical signals can enable important mid-infrared applications. However, the modest thermoelectric coefficient and weak temperature dependence of carrier transport in graphene hinder this goal.

“Here, we demonstrate mid-infrared graphene detectors consisting of arrays of plasmonic resonators interconnected by quasi-one-dimensional nanoribbons. Localized barriers associated with disorder in the nanoribbons produce a dramatic temperature dependence of carrier transport, thus enabling the electrical detection of plasmon decay in the nearby graphene resonators.

“Our device has a subwavelength footprint of 5 × 5 μm² and operates at 12.2 μm with an external responsivity of 16 mA W^–1 and a low noise-equivalent power of 1.3 nW Hz^–1/2 at room temperature. It is fabricated using large-scale graphene and possesses a simple two-terminal geometry, representing an essential step towards the realization of an on-chip graphene mid-infrared detector array.”