Ultralarge capacitance–voltage hysteresis and charge retention characteristics in metal oxide semiconductor structure containing nanocrystals deposited by ion-beam-assisted electron beam deposition

Amorphous silicon films are deposited by ion-beam-assisted electron beam deposition and subsequently oxidized by a rapid thermal oxidation process. The oxidized film contains a large density of nanocrystals specifically localized at a certain depth from the Si/SiOx interface, whereas no evidence of nanocrystals is found for oxidized films deposited without ion beam assistance. Such a marked contrast resulted from the enhancement of nucleation rate by ion beam irradiation. The metal-oxide-semiconductor structure utilizing the film shows an ultralarge capacitance–voltage hysteresis whose width is over 20 V. In addition capacitance–time measurement shows a characteristic capacitance transient indicating nondispersive carrier relaxation. The retention time shows a dependence on applied bias and the maximum time of ∼70 s is obtained near midgap voltage. The retention time dependence on applied bias and large capacitance–voltage hysteresis are attributed to direct tunneling of trapped charges in the deep traps of nanocrystals to the interface states.