EXCESS LOW-FREQUENCY NOISE IN HOPPING CONDUCTION.

The spectral density S(f) is calculated for resistivity fluctuations in a lightly doped compensated semiconductor at temperatures corresponding to hopping conduction. At frequencies much less than the carrier hopping frequency in a critical network (an infinite cluster which determines the conductivity of the semiconductor), the resistivity fluctuations are due to fluctuations in the number of carriers in the critical network. In an exponentially wide frequency range it is shown that S(f) varies directly as f** minus **s, where the exponent s less than 1 and depends on N//Da**3 (N//D being the impurity concentration and a the effective Bohr radius of the impurity centers).