Dandan Jiang

The growth of ZnMgO alloy films for deep ultraviolet detection

ZnMgO films are prepared by RF magnetron sputtering using a composite target and the Mg composition of the samples can be controlled easily even at a high growth temperature. The metal?semiconductor?metal photodetector based on the wurtzite Zn0.6Mg0.4O film exhibits a very low dark current (5?pA at |Vbias| = 3?V) and a high UV/visible rejection ratio (more than three orders of magnitude). The peak responsivity of the photodetector is at around 270?nm and a very sharp cutoff wavelength is at a wavelength of about 295?nm corresponding to the absorption edge of the Zn0.6Mg0.4O film.

MgxZn1?xO solar-blind photodetector grown by radio frequency magnetron sputtering

Cubic MgxZn1?xO thin films (x = 0.70) were grown on quartz substrates by radio frequency magnetron sputtering and a metal?semiconductor?metal structured photodetector was fabricated based on the film. The photodetector exhibited a dominant response peak at about 225?nm with a cutoff wavelength at about 230?nm, which lies in the solar-blind spectrum range (220?280?nm). A shoulder also appeared in the response spectrum at about 265?nm besides the dominant peak, which resulted from the phase separation in the Mg0.70Zn0.30O thin films as revealed by transmission electron microscopy. The photodetector showed very low dark current (2?pA at 3?V bias).

A study of cycling induced degradation mechanisms in Si nanocrystal memory devices.

The endurance of Si nanocrystal memory devices under Fowler-Nordheim program and erase (P/E) cycling is investigated. Both threshold voltage (V(th)) and subthreshold swing (SS) degradation are observed when using a high program or erase voltage. The change of SS is found to be proportional to the shift of V(th), indicating that the generation of interface traps plays a dominant role. The charge pumping and the mid-gap voltage methods have been used to analyze endurance degradation both qualitatively and quantitatively. It is concluded that high erase voltage causes severe threshold voltage degradation by generating more interface traps and trapped oxide charges.

Ultraviolet photodiode based on p-Mg0.2Zn0.8O/n-ZnO heterojunction with wide response range

P-Mg0.2Zn0.8O/n-ZnO heterojunction ultraviolet photodiode was fabricated on a sapphire substrate by plasma-assisted molecular beam epitaxy. The current–voltage measurement indicates that the heterojunction has a weak rectifying behaviour with a turn-on voltage of ~5 V. The spectral response measurement shows that the photodiode has a peak responsivity at around 340 nm, and it has a wide detection range in the ultraviolet region from 400 to 320 nm. The response in the long and short wavelength region is due to the contribution of the n-ZnO and p-MgZnO layers, respectively. The ultraviolet–visible rejection ratio (R340 nm/R500 nm) of two orders of magnitude was obtained at a reverse bias of 8 V.

Effect of post annealing on the band gap of MgxZn1-xO thin films

In this work, MgxZn1−xO (MZO) thin films were grown on quartz by rf magnetron sputtering technology. It was found that MZO films possess preferred c-axis orientation and exhibit hexagonal wurtzite structure up to a Mg composition of 44.26 mol%. Furthermore, the band gap determined by absorption spectra was smaller than the theoretical calculation for the as-grown MZO thin film. The band gap blueshifted initially and then redshifted with increasing the annealing temperature of the MZO films. The reason for the shift was attributed to the displacement, effusion of Mg atoms in the films and phase separation at different annealing temperatures.

Zn0.8Mg0.2O-based metal–semiconductor–metal photodiodes on quartz for visible-blind ultraviolet detection

Zn0.8Mg0.2O metal–semiconductor–metal ultraviolet photodiodes were fabricated on quartz by radio frequency magnetron sputtering. Dark current, spectral responsivity and pulse response experiments were carried out for the device. The photodetectors showed a peak responsivity at 330 nm. The ultraviolet-visible rejection ratio (R330 nm/R400 nm) was more than four orders of magnitude at 3 V bias. The photodetector showed fast photoresponse with a rise time of 10 ns and a fall time of 170 ns. In addition, the thermally limited detectivity was calculated to be 3.1 × 1011 cm Hz1/2 W−1 at 330 nm.

A novel junction-assisted programming scheme for Si-nanocrystal memory devices with improved performance

A novel drain-junction-assisted hot electron programming scheme has been proposed for Si nanocrystal memory devices. Different from the conventional channel hot electron (CHE) injection, two electron injection paths are responsible for the proposed scheme. Experimental results show that the new scheme has a nearly 1 V memory window increase and almost 300 times faster programming speed rather than the conventional CHE method. Meanwhile, improved data retention and endurance characteristics have also been achieved with the enlarged memory window, which is mainly due to less tunnel oxide degradation during the program/erase cycling. Therefore, the new scheme is shown to be more promising for Si nanocrystal memory application.

Investigation of charge loss mechanisms IN 3D TANOS cylindrical junction-less charge trapping memory

This paper presents a detailed simulation analysis of the charge loss mechanisms in 3D TANOS cylindrical junction-less charge trapping memory devices. For the programmed state, the role of tunneling through the bottom oxide and top oxide in vertical charge loss were compared, and the latter is found to be the dominant component. It is also found that lateral charge migration shows dependence on the shape of charge trapping layer. And the winding charge trapping layer shows favorable lateral migration performance. Simulation results show that lateral charge migration is more severe rather than vertical charge loss and must be focused with decreasing memory cell size. The result will give an guidance for high density 3D memory design optimization.

Cycling-Induced Peak-Like Interface State Generation in Si-Nanocrystal Memory Devices

The peaklike behavior of interface trap generation was observed in silicon-nanocrystal (Si-NC) memory during Fowler-Nordheim program/erase cycling. In addition to the two peaks at 0.3 and 0.85 eV from Pb0 centers, two extra peaks (0.45 and 0.7 eV) were also observed and suggested from Pb1 centers. In contrast, only Pb0 centers were observed in reference devices without Si-NCs. The result will be helpful to understand the effect of Si-NCs on the interface reliability.

A Novel Read Scheme for Read Disturbance Suppression in 3D NAND Flash Memory

A new read scheme is proposed to suppress read disturbance in unselected strings of three-dimensional (3D) vertical channel flash memories. This new scheme decreases the channel potential difference between select word-line (WL) and adjacent WL by more than 20% and the read disturb due to hot carrier injection in adjacent WL of selected WL is suppressed effectively by about 95%. Meanwhile, boosted channel potential during read operation has been preserved to improve soft programming read disturbance by more than 85% in non-adjacent unselected memory cells, owing to the reduced electric field across tunnel oxide. Compared with the conventional scheme, the proposed scheme leads to a significant improvement in read disturbance characteristics with a shorter read period as well as a simplified waveform of read operation.