[en] In this work, Ge nanocrystals (nc-Ge) embedded in SiO₂ thin films have been synthesized by ion implantation. Both the higher and the lower implantation dose/energy samples exhibit significant memory effect as a result of charge trapping in the nc-Ge. Under a negative gate voltage, either electron trapping or hole trapping dominates, depending on the magnitude of gate voltage and charging time as well as the distribution of nc-Ge. However, under a positive gate voltage, only electron trapping is observed, and the flat-band voltage shift is also affected by the nc-Ge distribution. These results demonstrate that the unconventional memory effect can be modulated by the distribution of nc-Ge.

[en] We have investigated the current conduction of NiO thin film embedded with Ni nanocrystals (nc-Ni) and the influence of charging in the nc-Ni/NiO thin film on the current transport. The hole trapping in the thin film under a negative charging voltage is found to greatly increase the current conduction measured at a positive voltage due to the enhancement of electric field at the interface between the thin film and Si substrate. Moreover, the current-voltage (I-V) characteristic follows a power-law relationship. In addition, the dc resistance of the thin film strongly depends on the magnitude of the charging voltage and charging time. These results could be used to realize a charging-controlled resistive memory effect.

[en] Al nanocrystals (nc-Al) embedded in AlN thin films have been synthesized by rf magnetron sputtering. The influence of ultraviolet (UV) illumination on electrical characteristics of the nc-Al/AlN thin film system has been investigated. It is shown that the UV illumination could lead to a random change in the conductance of the thin film system. The change in the conductance is attributed to the charge trapping and detrapping in the nc-Al due to the UV illumination

[en] Using a two-step fabrication technique (pulsed laser deposition (PLD) and H₂ surface treatment), we fabricated ZnO thin films that could emit ultra-strong green emission with coexistence of random lasing phenomenon. After PLD deposition, the as-prepared undoped ZnO thin films (200-500 nm) were annealed in Ar 95%-H₂5% ambient at 500 °C. The H₂ treatment led to the formation of a porous structure that creates substantial optical cavities (diameter ∼1.3 µm). Surprisingly, these optical cavities tremendously amplified the green emission rather than ultraviolet (UV) emission. There was insignificant change in emission intensity after high-temperature annealing (700 °C) in O₂ and acetone dipping, indicating the samples are thermally and chemically stable. The samples exhibited a high quantum yield of 32%. We studied the origin of this ultra-strong green emission using low-temperature photoluminescence, extensive structural study and cyclic annealing. The results suggested that neither hydrogen nor V_O plays a role in green emission. The green emission was attributed mainly to the complex defects and the presence of structural defects in the porous structure. In addition, we demonstrated the feasibility of large-scale green emission ZnO fabrication via micro-size patterning, paving a way to practical optoelectronic applications. (paper)

[en] A densely stacked silicon nanocrystal layer embedded in a SiO₂ thin film is synthesized with Si ion implantation. The dielectric functions of the nanocrystal layer are determined with spectroscopic ellipsometry. The dielectric functions show a significant suppression as compared to that of bulk crystalline Si. Thermal annealing leads to an evolution of the dielectric functions from the amorphous towards crystalline state. For an insufficient annealing, the dielectric functions present a single broad peak, being similar to that of amorphous Si. However, a sufficient annealing leads to the emergence of the two-peak structure which is similar to that of bulk crystalline Si. In addition, the dielectric functions increase with annealing with a trend towards bulk Si

[en] The authors report the photon-induced conduction modulation in SiO₂ thin films embedded with germanium nanocrystals (nc-Ge). The conduction of the oxide could be switched to a higher- or lower-conductance state by a ultraviolet (UV) illumination. The conduction modulation is caused by charging and discharging in the nc-Ge due to the UV illumination. If the charging process is dominant, the oxide conductance is reduced; however, if the discharging process is dominant, the oxide conductance is increased. As the conduction can be modulated by UV illumination, it could have potential applications in silicon-based optical memory devices

[en] A layer of Ge nanocrystals (nc-Ge) distributed in the gate oxide near the gate of a metal-oxide-semiconductor structure is synthesized with low-energy Ge ion implantation followed by thermal annealing at 800 deg. C. The behaviors of charge trapping and charge retention in the nc-Ge have been studied. For a positive charging voltage, only electron trapping occurs, and the trapped electrons show a long retention time. However, for a negative charging voltage, both the hole trapping and electron trapping occur simultaneously, and the hole trapping is dominant if the magnitude of the charging voltage is small or the charging time is short. Due to the relatively easier loss of the trapped holes, the net charge trapping in the nc-Ge exhibits a continuous shift toward a more negative value with the waiting time

[en] In this letter, Ni-rich NiO thin film is deposited on p-type Si substrate by dc magnetron sputtering to form a metal-insulator-semiconductor structure. The charge trapping in the Ni nanocrystals (nc-Ni) embedded in NiO matrix induces a flatband voltage shift and capacitance modulation, which could be used for memory applications. The charging of nc-Ni depends on the voltage polarity, as well as the charging time and magnitude of gate voltage. The capacitance modulation can be described by an equivalent circuit model.

[en] Ge nanoclusters distributed in the gate oxide near the gate of a metal-oxide-semiconductor structure were fabricated by a low-energy ion implantation technique. Secondary ion mass spectroscopy and x-ray photoemission spectroscopy measurements show that thermal annealing causes the diffusion of Ge in the oxide towards the Si substrate as well as oxidation of the Ge nanoclusters. The changes in the structural and chemical properties of the Ge nanoclusters are found to seriously affect the charge storage in the nanoclusters. It is observed that the electron trapping capability decreases with the annealing temperature as a result of the oxidation of Ge nanoclusters. On the other hand, the charge loss increases with the annealing temperature, but it decreases when the annealing temperature is higher than 1000 deg. C. This behaviour is attributed to the two competing mechanisms, i.e. the formation of leakage paths formed by the Ge atoms diffused in the gate oxide and the blocking of the leakage paths due to the oxidation of the Ge leakage sites.

[en] The effect of short-duration ultraviolet (UV) exposure on the threshold voltage (V_th) of amorphous indium gallium zinc oxide thin film transistors (TFTs) and its recovery characteristics were investigated. The V_th exhibited a significant negative shift after UV exposure. The V_th instability caused by UV illumination is attributed to the positive charge trapping in the dielectric layer and/or at the channel/dielectric interface. The illuminated devices showed a slow recovery in threshold voltage without external bias. However, an instant recovery can be achieved by the application of positive gate pulses, which is due to the elimination of the positive trapped charges as a result of the presence of a large amount of field-induced electrons in the interface region