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Complex AC-conductance, $\sigma^{AC}$, in the systems with denseGe$_{0.7}$Si$_{0.3}$ quantum dot (QD) arrays in Si has been determined fromsimultaneous measurements of attenuation, $\Delta\Gamma=\Gamma(H)-\Gamma(0)$,and velocity, $\Delta V /V=(V(H)-V(0)) / V(0)$, of surface acoustic waves (SAW)with frequencies $f$ = 30-300 MHz as functions of transverse magnetic field $H\leq$ 18 T in the temperature range $T$ = 1-20 K. It has been shown that in thesample with dopant (B) concentration 8.2$ \times 10^{11}$ cm$^{-2}$ attemperatures $T \leq$4 K the AC conductivity is dominated by hopping betweenstates localized in different QDs. The observed power-law temperaturedependence, $\sigma_1(H=0)\propto T^{2.4}$, and weak frequency dependence,$\sigma_1(H=0)\propto \omega^0$, of the AC conductivity are consistent withpredictions of the two-site model for AC hopping conductivity for the case of$\omega \tau_0 \gg $1, where $\omega=2\pi f$ is the SAW angular frequency and$\tau_0$ is the typical population relaxation time. At $T >$ 7 K the ACconductivity is due to thermal activation of the carriers (holes) to themobility edge. In intermediate temperature region 4$ < T<$ 7 K, where ACconductivity is due to a combination of hops between QDs and diffusion on themobility edge, one succeeded to separate both contributions. Temperaturedependence of hopping contribution to the conductivity above $T^*\sim$ 4.5 Ksaturates, evidencing crossover to the regime where $\omega \tau_0 < $1. Fromcrossover condition, $\omega \tau_0(T^*)$ = 1, the typical value, $\tau_0$, ofthe relaxation time has been determined.Comment: revtex, 3 pages, 6 figure

AC Conductance in Dense Array of the Ge0.7Si0.3 Quantum Dots in Si