VERY LOW-NOISE PHOTODETECTOR BASED ON THE SINGLE ELECTRON TRANSISTOR

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 (lambda = 650 nm). From the ''dark current'' noise of 0.06 e/s, we estimate a dc noise-equivalent power NEP = 2 x 10(-21) W/square-root Hz for infrared light with lambda = 30 mum, and from this calculate a detectivity D* = 8 x 10(17) cm. square-root Hz/W.