  Using acoustic methods we have measured nonlinear AC conductance in 2D arrays
of Ge-in-Si quantum dots. The combination of experimental results and modeling
of AC conductance of a dense lattice of localized states leads us to the
conclusion that the main mechanism of AC conduction in hopping systems with
large localization length is due to the charge transfer within large clusters,
while the main mechanism behind its non-Ohmic behavior is charge heating by
absorbed power.
