Rapid-thermal-annealing effect on lateral charge loss in metal–oxide–semiconductor capacitors with Ge nanocrystals

The rapid-thermal-annealing effect on lateral charge loss in metal–oxide–semiconductor capacitors with Ge nanocrystals is investigated by means of capacitance-voltage $(C–V)$ and capacitance decay measurements. The $C–V$ curves show the hysteresis indicating the charge storage effect in Ge nanocrystals. The hysteresis width shows strong annealing temperature dependence and shows the maximum at 700 °C meaning the maximum nanocrystal density. Capacitance decay experiment at flat-band voltage shows that the decay is dominated by two decay mechanisms. The initial fast discharge is more significant for samples annealed at lower temperatures. The cross-sectional transmission electron microscopic observations show the quasi-continuous Ge layer with Ge nanocrystals and Ge-rich amorphous regions for samples annealed at lower temperatures. Therefore, the fast discharging is attributed to lateral charge loss of insufficiently localized nanocrystals. On the other hand, the slow discharge is attributed to tunneling out of the stored charges in completely localized Ge nanocrystals via the tunneling barrier.