RESUMEN
The memory devices constructed from the Ge-nanoclusters embedded GeO(x) layer deposited by the laser-assisted chemical vapor deposition (LACVD) system were fabricated. The Ge nanoclusters were observed by a high-resolution transmission electron microscopy. Using the capacitance versus voltage (C-V) and the conductance versus voltage (G-V) characteristics measured under various frequencies, the memory effect observed in the C-V curves was dominantly attributed to the charge storage in the Ge nanoclusters. Furthermore, the defects existed in the deposited film and the interface states were insignificant to the memory performances. Capacitance versus time (C-t) measurement was also executed to evaluate the charge retention characteristics. The charge storage and retention behaviors of the devices demonstrated that the Ge nanoclusters grown by the LACVD system at low temperature are promising for memory device applications.
RESUMEN
The capacitance-voltage (C-V) and charge retention characteristics of the metal-insulator-semiconductor (MIS) structure, in which the insulator layer was composed of silicon nanocluster-embedded silicon nitride, were studied. The memory effect of this MIS structure was dominantly attributed to the charge storage in the silicon nanoclusters. The relation between the flatband voltage shift and the amount of charges stored in the nanocluster-embedded insulator layer was discussed. The capacitance-time (C-t) relation of MIS structures, conventionally used to follow the discharge process, was further analyzed, indicating that care should be taken in the C-t measurement for obtaining correct discharging behavior. Then the charge retention characteristics of the fabricated MIS structures under various charging conditions were derived by the capacitance-time (C-t) measurement. The results showed that the devices, charged for a longer time or under a lower charging voltage, discharge slower. The observed charge retention behaviors can be reasonably attributed to the spatial distribution of silicon nanoclusters in the silicon nitride layer and the dispersion of the nanocluster sizes
RESUMEN
The structure of nanocrystalline Y2O3:Eu prepared by a combustion reaction was analyzed by XRD and high-resolution electron microscopy. Compared with a large-scale particles, 5-nm Y2O3:Eu particles presented as distorted crystallite and rough surfaces. Luminescent and absorption properties of nano-Y2O3:Eu showed remarkably particle size effects. At Y2O3:Eu particle sizes smaller than 10 nm some new results were observed: (a) a red shift of the charge-transfer-state absorption; (b) new emission bands of Eu3+ in the 5D0 --> 7F2 region; (c) luminescent decay of energy level 5D0 of Eu3+ turning to a two-step exponential; and (d) a pronounced increase in quenching concentration and much lower phonon density compared with those of the bulk material. All these phenomena can be attributed to the effect of the softened lattice and surface state of the nanomaterial. The latter was confirmed by stronger excitation by the host absorption after the surface modification.