Formation of stable charge regions in an array of germanium nanocrystallites inside SiO$_2$ using electrostatic force microscopy

The objects of investigations are germanium nanocrystallites formed inside a SiO$_2$ layer by ion implantation followed by high-temperature annealing. Germanium nanocrystallites inside a thin (30 nm) layer of thermal SiO$_2$ oxide are charged by means of scanning probe microscopy, and the resulting charged zones are visualized and analyzed. It is shown that stable charge regions up to 30 nm in diameter that consist of several charged germanium nanocrystallites can be formed under the probe of an atomic-force microscope. It turns out that the ability of the germanium nanocrystallites to keep the induced charge is extremely sensitive to the intercrystallite distance and the presence of defect centers in the SiO$_2$ layer. This is explained by the fact that the charge escapes from the germanium nanocrystallites by tunneling either between adjacent crystallites or through defect centers in the SiO$_2$.