Diffusion, mobility fluctuation, and island models of flicker noise

Connections and equivalences among the diffusion, mobility fluctuation, and island theories of the flicker noise are shown, and the usual division in two model categories, based on the carrier-number and -mobility fluctuations, is so removed. To this end, the diffusion-noise theory, as well as the previous island model, is applied to conducting media containing localized states, the drift-velocity cross-correlation functions of the hemimicroscopic motion of each carrier, which at random is trapped and released by the islands, are computed, and, finally, the voltage noise spectrum at the device terminals is achieved as a sum of Lorentzian spectra by means of the Wiener-Khintchine theorem and the impedance-field method. It partly coincides with the one yielded, in the case of defect sizes smaller than the Debye length, by the island model through the charge-conservation principle, the Langevin method, the Schottky theorem, and the dipole-current and impedance-field methods applied directly to each island. For both approaches, in order to obtain the total noise spectrum in the flickerlike form 1/f^γ, the defect relaxation times, which the diffusion theory cannot yield, and the computation methods of the island model are to be employed. The diffusion-noise model, instead, by the computation of the cross-correlation functions of the hemimicroscopic motion allows one to ascribe the flicker-noise origin also to the hemimicroscopic mobility fluctuation of each carrier due just to the stochastic process of its trapping and releasing by the islands during the drift displacement. Therefore the general validity of the island model, previously shown by its ability to yield an unitary synthesis of the flicker, burst, and generation-recombination noises, is now further extended and strengthened by its capability to account for and to contain other noise-analysis methods, such as the diffusion-noise and mobility-fluctuation models.