Dev.SN

janrinok writes:

Science Daily is carrying a story about a recently developed, ultra-thin light detector working in the infra-red (terahertz) band. This discovery, made at Vienna University of Technology, now opens up the possibility of integrating a light detector for terahertz radiation into a chip. From the report:

"With conventional fabrication methods, large arrays of such detectors can be built," Professor Karl Unterrainer explains. They do not take up much space: 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.

"Ultra-thin layered semiconductor systems have the great advantage, that their electronic properties can be very precisely tuned," says Unterrainer. By selecting suitable materials, by tuning the thickness of the layers and the geometry of the device, the behaviour of the electrons in the system can be influenced. That way, quantum cascade lasers can be built, in which the electrons jump from layer to layer and emit a photon with each jump. Also, light detectors can be created, with a selective sensitivity to one particular wavelength.

The problem, however, is that quantum physics prohibits photons with a certain directions of oscillation (polarization) from interacting with the electrons of the semiconductor system. Light which hits the layered surface head-on, cannot influence the electron in the semiconductor. Therefore a method is required to rotate the polarization of the incident light, so that it can be detected in the semiconductor layers.