A joint team of scientists from Royal Holloway University of London, UK, Tokyo University, Japan, and the Institute for Solid State Physics, Russia, has fabricated a single-photon detector for terahertz radiation, which could help to bring about prolific new applications in chemistry, physics and biology.

Detector operation

An incoming terahertz photon incident at the patterned semiconductor heterostructure (for more details, click on the image) is absorbed by the electron gas so that the photon energy is transferred to a plasma wave localized inside the quantum dot (QD). The plasma wave may decay to an electron-hole pair in such a way so that one of the electrons leaves the QD. Because of this, the QD undergoes a transition to a meta-stable charge excited state and the electrostatic potential in close proximity to the QD changes stepwise. The SET probes this change in potential and indicates absorption of the photon. Thus, counting of terahertz photons can be performed.

In fact, only one of 1000 photons is counted in this way, but even with such low quantum efficiency, the sensor has an unprecedented high sensitivity that exceeds existing terahertz sensors by a few orders of magnitude.

More details are available in the journal Nanotechnology.