Gain dependence of the noise in the single electron transistor

An extensive investigation of low frequency noise in single electron transi stors as a function of gain is presented. Comparing the output noise with g ain for a large number of bias points, it is found that the noise is domina ted by external charge noise. For low gains we find an additional noise con tribution which is compared to a model including resistance fluctuations. W e conclude that this excess noise is not primarily due to resistance fluctu ations. For one sample, we find a low minimum charge noise of q(n) approxim ate to 2 x 10(-5) e/root Hz at a frequency of 4.4 kHz. (C) 1999 American In stitute of Physics. [S0021-8979(99)05815-6].