Conductive AFM microscopy study of the carrier transport and storage in Ge nanocrystals grown by dewetting

A combined conductive atomic force microscope (C-AFM)/scanning electron microscope (SEM) has been used to study the electric transport and retention mechanisms through Ge nanocrystals (NCs). The NCs were formed by a two-step dewetting/nucleation process on a silicon oxide layer grown on n-doped (001) silicon substrate. Without preliminary e-beam irradiation, electric images are obtained only with bias voltages larger than 8 V. This is due to the barrier height introduced by the presence of the native oxide on NCs and of the oxide layer on which the NCs are grown. After acquisition of an e-beam-induced current image, electric images (e-beam off) can be easily obtained at low bias voltages because of the trap creation in the oxide layer. We show that the critical threshold voltage to detect a current through the NCs decreases with NCs size. The band diagram of the contact in the presence of a p-doped diamond coated tip shows that the conduction mechanism is dominated by holes. At last we show a good memory effect with charge/discharge in the NCs resulting in a long retention time.