Nonlinear high-frequency hopping conduction in two-dimensional arrays of   Ge-in-Si quantum dots: Acoustic methods
  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. 
I.L. Drichko, A.M. Diakonov, V.A. Malysh, I.Yu. Smirnov, E.S. Koptev,   A.I. Nikiforov, N.P. Stepina, Y.M. Galperin, and J. ...
cond-mat.mes-hall