2 3 N ov 1 99 9 Fluctuation - Stimulated Variable - Range Hopping

Qualitatively new transport mechanism is suggested for hopping of carriers according to which the variable-range hopping (VRH) arises from the resonant tunneling between transport states brought into resonance by Coulomb potentials produced by surrounding sites with fluctuating occupations. A semiquantitative description of the hopping transport is given based on the assumption that fluctuations of energies of hopping sites have spectral density 1/f. Recently, it was suggested that fluctuations of site occupations in thermal equilibrium can cause essential energy fluctuations for sites participating in the hopping transport [1,2]. This idea was used to explain the low-frequency noise with spectral density 1/f reported for hopping conductivity in p-Ge(Ga) and n-Ge(As) [1]. Due to the long-range character of the Coulomb potential, fluctuations in occupation numbers of some sites lead to essential fluctuations of energies of the surrounding sites. In Refs.[1,2], an attempt has been done to distinguish between the sites participating in the hopping transport (transport sites) and fluctuators, the latter being the sites which produce energy fluctuations on the transport sites, but do not directly participate in hopping processes. Comparison of experimental data with simple theoretical estimates [2] shows that the noise level is so large that each effective resistor on the transport cluster has relative fluctuations of the 1