Ming Yang

Strong violet and green-yellow electroluminescence from silicon nitride thin films multiply implanted with Si ions

Strong visible electroluminescence (EL) has been observed from a 30 nm silicon nitride thin film multiply implanted with Si ions and annealed at 1100 °C. The EL intensity shows a linear relationship with the current transport in the thin film at lower voltages, but a departure from the linear relationship with a quenching in the EL intensity is observed at higher voltages. The EL spectra show two primary EL bands including the predominant violet band at ∼3.0 eV (415 nm) and the strong green-yellow band at ∼2.2 eV (560 nm). Two weak bands including the ultraviolet band at ∼3.8 eV and the near infrared band at ∼1.45 eV emerge at high voltages. The evolution of each EL band with the voltage has been examined. The phenomena observed are explained, and the EL mechanisms are discussed.

Impact of programming mechanisms on the performance and reliability of nonvolatile memory devices based on Si nanocrystals

A nonvolatile memory based on silicon nanocrystals (nc-Si) synthesized with very-low-energy Si/sup +/ implantation is fabricated, and the memory performance under the programming/erasing of either Fowler-Nordheim (FN)/FN or channel hot electron (CHE)/FN at both room temperature and 85/spl deg/C is investigated. The CHE programming has a larger memory window, a better endurance, and a longer retention time as compared to FN programming. In addition, the CHE programming yields less stress-induced leakage current than FN programming, suggesting that it produces less damage to the gate oxide and the oxide/Si interface. Detailed discussions on the impact of the programming mechanisms are presented.

Influence of charge trapping on electroluminescence from Si-nanocrystal light emitting structure

We report a study on the influence of charge trapping on electroluminescence (EL) from Si nanocrystal (nc-Si) distributed throughout a 30nm SiO2 thin film synthesized by Si+ implantation into an oxide film thermally grown on a p-type Si substrate. The electron and hole trapping in the nc-Si located near the indium tin oxide gate and the Si substrate, respectively, cause a reduction in the EL intensity. The reduced EL intensity can be recovered after the trapped charges are released. A partial recovery can be easily achieved by the application of a positive gate voltage or thermal annealing at hot temperatures (e.g., 120°C) for a short duration. The present study highlights the impact of charging in the nc-Si on the light emission efficiency and its stability of nc-Si light-emitting devices.

Charging effect of Al2O3 thin films containing Al nanocrystals

In this work, Al2O3 thin film containing Al nanocrystals (nc-Al) is deposited on Si substrate by radio frequency sputtering to form a metal-insulator-semiconductor structure. Both electron and hole trapping in nc-Al are observed. The charge storage ability of the nc-Al/Al2O3 thin films provides the possibility of memory applications. Charging in the nc-Al also leads to a change in the dc resistance of the thin films, namely, the electron trapping in the nc-Al leads to an increase in the resistance, whereas the resistance is reduced if there is hole trapping in the nc-Al.

Charging-Induced Changes in Reverse Current–Voltage Characteristics of Al/Al-Rich

An Al-rich Al₂O₃ thin film was deposited on a p-type silicon substrate by radio frequency sputtering to form Al/Al-rich Al₂O₃/p-Si diodes. The current-voltage (<i>I</i>- <i>V</i>) characteristics of the diodes were determined by carrier injection from either the Si substrate or the Al gate and by carrier transport along the tunneling paths formed by Al nanocrystals distributed in the oxide layer. The reverse <i>I</i>- <i>V</i> characteristics were greatly affected by the charge trapping in the oxide layer, i.e., the electron trapping significantly reduced the reverse current while the hole trapping enhanced the current significantly. However, the charge trapping did not produce a large change in the forward <i>I</i>-<i>V</i> characteristic.

\hbox{Al}_{2}\hbox{O}_{3}/\hbox{p-Si}

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°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.

Diodes

Relationship between current transport and electroluminescence (EL) in the system of excess Si distributed in SiO2 thin films synthesized with low-energy ion implantation has been examined. A linear relationship is found, and both of them follow a power law and are determined by the concentration and distribution of the excess Si in the oxide films. With the knowledge of the dependence of the transport on the concentration and distribution of the excess Si, one can predict the effect of the implantation recipe on the EL intensity.

Charge trapping and retention behaviors of Ge nanocrystals distributed in the gate oxide near the gate synthesized by low-energy ion implantation

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.

Relationship Between Current Transport and Electroluminescence in

A write-once-read-many-times (WORM) memory device was realized based on the charging-controlled modulation in the current conduction of Al/Al-rich Al2O3 /p-type Si diode. A large increase in the reverse current of the diode could be achieved with a negative charging voltage, e.g., charging at -25 V for 1 ms results in a current increase by about four orders. Memory states of the WORM device could be altered by changing the current conduction with charge trapping in the Al-rich Al2O3 layer. The memory exhibited good reading endurance and retention characteristics.

\hbox{Si}^{+}

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.