Real Time Read‐Out of Single Photon Absorption by a Field Effect Transistor with a Layer of Quantum Dots

We present results of photon counting with a single photon detector based on field effect transistor with a layer of quantum dots in close proximity to the channel. Detection of a photon is achieved when photo‐hole is captured by negatively charged InAs dot leading to a step‐like increase of the current in the channel of the transistor. We use a transimpedance amplifier with a cryogenic stage and ac coupling on the input to convert the current steps of 1–2 nA height into voltage peaks with microsecond time resolution. We show that single photon counting with 0.3% efficiency, dark count rate below 10−8 ns−1 is then achieved, while the jitter limited by the circuit can be as low as 8.5 ns.