Large capacitance-voltage hysteresis loops in SiO2 films containing Ge nanocrystals produced by ion implantation and annealing

Abstract

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