We report investigations of the hole transport in arrays of Ge quantum dots
buried in Si. Based on measurements of the temperature dependence of the c
onductance, the charge-transfer mechanism is proposed to be due to variable
-range hopping between the dots with the typical hopping energy determined
by inter-dot Coulomb interaction. We find that putting a metal plane close
to the dot layer causes a crossover from Efros-Shklovskii variable-range ho
pping conductance to two-dimensional Mott behavior as the temperature is re
duced. At the crossover temperature the hopping activation energy is observ
ed to fall off. The experimental results are explained by screening of long
-range Coulomb potentials and give evidence for strong electrostatic intera
ction between dots in the absence of screening. Conductance oscillations wi
th gate voltage resulting from successive loading of holes into the dots ar
e observed in the field-effect structures.