We describe a mechanism, which links the long-range potential fluctuations induced by charged defects to the low frequency resistance noise widely known as 1/f noise. This mechanism is amenable to the first principles microscopic calculation of the noise spectrum, which includes the absolute noise intensity. We have performed such a calculation for the thin films of hydrogenated amorphous silicon (a-Si:H) under the condition that current flows perpendicular to the plane of the films, and found a very good agreement between the resulting theoretical spectra and the spectra obtained in our own experiments. The mechanism described is quite general. It should be present in a broad class of systems containing poorly screened charged defects.
For a given defect, the rate of charge fluctuations depends on the activation barrier, which an electron should overcome in order to escape from that defect. This rate, in turn, depends on the local random potential. Therefore, our study also introduces a new experimental method of characterizing the random potential landscapes in the vicinity of deep defects.