Metamaterials set to enable terahertz radiation sensors
1 min read
Thin layers of semiconductors can turn electrical voltage into light and vice versa, serve as light detectors. However, it has been hard to couple light into these layered semiconductor systems. Now, researchers at at Vienna University of Technology say they have solved the problem using metamaterials, whose microscopic structure allows light in the terahertz range to be manipulated.
"Ultra thin layered semiconductor systems have the advantage that their electronic properties can be tuned precisely", said Professor Karl Unterrainer, who added that, by selecting suitable materials, tuning the thickness of the layers and the device's geometry, electron behaviour in the system can be influenced. This allows quantum cascade lasers to be built in which electrons jump from layer to layer and emit a photon with each jump. Similarly, light detectors can be created that are sensitive to one particular wavelength.
But quantum physics prohibits photons with a particular polarisation from interacting with electrons in the semiconductor system. Light which hits the layered surface head on cannot influence the electron in the semiconductor. This required a method of rotating the polarisation of incident light so that it could be detected in the semiconductor layers.
This has been accomplished using metamaterials – ordered geometric structures with a periodicity smaller than the wavelength of the incident light.
The discovery is said to open up the possibility of integrating a light detector for terahertz radiation into a chip. "With conventional fabrication methods, large arrays of such detectors can be built", Prof Unterrainer said. Layers with a thickness in the order of magnitude of nanometers are enough to detect light – the detector is more than a thousand times thinner than the wavelength of the light which is being detected.
