Researchers at Toshiba Research Europe in Cambridge, UK, have developed a single-photon detector based on quantum dots. It is the first time quantum dots have been used to detect individual photons at visible or near-infrared wavelengths, Andrew Shields of Toshiba told the CLEO conference in San Francisco this week. Single photons are usually detected by amplifying a signal with a photomultiplier tube or avalanche photodiode. This new technique avoids avalanche-type processes, which makes the device less prone to noise.
The quantum dot device consists of a transistor made of different layers of gallium arsenide and aluminium gallium arsenide. One of the layers consists entirely of quantum dots just nanometers across. The quantum dots are extremely sensitive to photons. A photon hitting the detector liberates an electron trapped in the one of the dots. A nearby conducting channel, just a few nanometres above the quantum dot layer, picks up the electron – which causes a detectable change in the resistance of the channel. Currently the device only operates at 4 Kelvin but the team hopes to develop detectors that will work at 77 Kelvin and, eventually, at room temperature.
