Charge retention effect in metal–oxide–semiconductor structure containing Si nanocrystals prepared by ion-beam-assisted electron beam deposition

An amorphous Si layer prepared by ion-beam-assisted electron beam deposition (IBAED) method is oxidized by a rapid thermal oxidation technique. We observe a nanocrystal band located at about 4 nm from the Si/SiOx interface by cross-sectional transmission electron microscope observation. The metal–oxide–semiconductor (MOS) structure employing the oxide layer with the nanocrystal band exhibits a large capacitance–voltage hysteresis indicative of trapping of electrons/holes. In contrast, a relatively small capacitance–voltage hysteresis is found for the MOS diode prepared by conventional electron beam deposition (EBD) without ion-beam assistance. Such a marked difference shows that the ion-beam irradiation plays an important role in the formation of nuclei, which would grow to nanocrystals during subsequent rapid thermal oxidation process. Interestingly, the MOS prepared by IBAED shows a characteristic capacitance transient behavior, indicative of non-dispersive carrier relaxation. In addition, the charge retention times shows a bias dependence and a maximum of 72 s near the mid-gap voltage. Such a bias-dependent retention time is interpreted in terms of the tunneling of trapped charges in nanocrystals through empty interface states.