Treatment of microscopic fluctuations in noise theory

A new method is introduced and used to calculate the statistics of the microscopic fluctuations of charge carriers in devices. By expressing the fluctuations of the carriers in terms of elementary transfer fluctuations, we are able to separate the induced fluctuations from the spontaneous fluctuations experienced by such carriers. This enables us to treat correlation effects in the dynamical portion of the problem and reserve for the statistical portion only well-defined, uncorrelated random forces whose statistics are readily calculated. The method includes all important correlation effects as well as multiple-decay-time relaxation effects and, thus, it fills a gap in the Langevin method as well as in the impedance-field method of calculating noise in devices. The method is suitable for treating nonstationary as well as stationary noise, and in some cases can be used directly on macroscopic problems. We also present a derivation of a recently introduced expression for diffusion noise of carriers whose mobility is a nonlinear function of applied electric field. This microscopic approach may further illustrate the origin, nature, and treatment of fluctuations in devices.