Large capacitance-voltage hysteresis loops in SiO ₂ films containing Ge nanocrystals produced by ion implantation and annealing

Metal-oxide-semiconductor structures containing Ge nanocrystals (NCs) of 3-4 nm diameter and 2× 1012 cm-2 density are shown to exhibit capacitance-voltage hysteresis of 20.9 V, one of the largest observed in Ge-NC based nonvolatile memories. The Ge NCs were fabricated in an oxide of 30 nm thickness by ion implantation with 30 keV Ge2- ions to an equivalent fluence of 1× 1016 Ge cm-2 followed by annealing at 950 °C for 10 min. Secondary ion mass spectroscopy and transmission electron microscopy demonstrate the existence of Ge NCs whose average distance from the SiO2 Si interface is about 6.7 nm. It is shown that the memory effect is a likely consequence of charge trapping at Ge NCs and that it is enhanced by accurately controlling the distribution of Ge NCs with respect to the Si SiO2 interface.