Very low noise photodetector based on the single electron transistor

Abstract
We demonstrate the use of the single electron transistor (SET) as an amplifier for a photodetector operated at 20 mK. The unparalleled low input noise of the SET permits the observation of very small numbers of charge carriers generated in a bulk p‐type Si substrate. We present data showing the response of the detector when it is illuminated by extremely low levels of red light (λ=650 nm). From the ‘‘dark current’’ noise of 0.06 e/s, we estimate a dc noise‐equivalent power NEP=2×10−21 W/√Hz for infrared light with λ=30 μm, and from this calculate a detectivity D*=8×1017 cm⋅√Hz/W.