Large capacitance-voltage hysteresis loops in SiO_2 films containing Ge nanocrystals produced by ion implantation and annealing

摘要

Metal-oxide-semiconductor structures containing Ge nanocrystals (NCs) of 3-4 nm diameter and 2 x 10~(12) 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 Ge_2~- ions to an equivalent fluence of 1 x 10~(16) Ge cm~(-2) followed by annealing at 950℃ for 10 min. Secondary ion mass spectroscopy and transmission electron microscopy demonstrate the existence of Ge NCs whose average distance from the SiO_2/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/SiO_2 interface.