  Issues of Ge hut cluster nucleation and growth at low temperatures on the
Ge/Si(001) wetting layer are discussed on the basis of explorations performed
by high resolution STM and in-situ RHEED. Data of HRTEM investigations of Ge/Si
heterostructures are presented with the focus on low-temperature formation of
perfect multilayer films. Exploration of the photovoltaic effect in Si
p--i--n-structures with Ge quantum dots allowed us to propose a new approach to
designing of infrared detectors. First data on THz dynamical conductivity of
Ge/Si(001) heterostructures in the temperature interval from 5 to 300 K and
magnetic fields up to 6 T are reported.
