Combining Technologies Creates Ultrathin Light Detectors

A first-ever combination of technologies has resulted in the creation of an extremely thin light detector.

By integrating metamaterials and quantum cascade structures, a team from the Vienna University of Technology has coupled light into the ultrathin systems of semiconductor layers that comprise the devices, a task that has proved difficult in past studies.

The semiconductor layers can turn electrical voltage into light, and they can also serve as light detectors. With the new technique, the researchers use metamaterials whose specific microscopic structure can manipulate light in the terahertz range.

The metamaterial couples the incident light to the semiconductor. It can then be converted into an electric signal. Courtesy of Vienna University of Technology.

“Ultrathin layered semiconductor systems have the great advantage that their electronic properties can be very precisely tuned,” said Karl Unterrainer, a professor at TU Vienna.

He added that tuning the thickness of the layers as well as the geometry of the device can influence the behavior of the electrons in the system. This allows for the creation of quantum cascade lasers in which electrons jump between layers and emit a photon each time.

Light detectors could be designed with a selective sensitivity to one particular wavelength.

The problem, however, is that quantum physics prevents photons with certain polarizations, such as those that hit the layered surface head-on, from interacting with the electrons of the semiconductor system. Metamaterials whose thickness and geometry can be tuned to rotate the polarization of the incoming light can enable the wavelengths to interact with the electrons inside.

In their experiments, the researchers used terahertz or infrared light, which could play an important role in next-generation computer technology. However, working with terahertz waves has proved difficult.

The new innovation at Vienna UT offers the potential to integrate a terahertz light detector into a chip.

“With conventional fabrication methods, large arrays of such detectors can be built,” Unterrainer said, noting that the detectors do not take up much space.

The research was published in Nature Scientific Reports (doi: 10.1038/srep04269).

For more information, visit: www.tuwien.ac.at.