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 similar to 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. (C) 2001 American Institute of Physics.