Ninglin Zhang

Memory and negative photoconductivity effects of Ge nanocrystals embedded in ZrO2/Al2O3 gate dielectrics

Metal–insulator–semiconductor (MIS) structures containing Ge nanocrystals embedded in high permittivity dielectrics (ZrO2/Al2O3) are fabricated by electron-beam evaporation method. Capacitance–voltage (C–V) and I–V characteristics of the fabricated MIS structures are investigated in the dark and under illumination. Charge storing and negative photoconductivity effects of the Ge nanocrystals are experimentally demonstrated by the hysteresis in the C–V curves and the decrease of the current under illumination at a given voltage, respectively.

Linear and third-order nonlinear optical absorption of amorphous Ge nanoclusters embedded in Al2O3 matrix synthesized by electron-beam coevaporation

Amorphous germanium (α-Ge) nanoclusters embedded in Al2O3 matrix are synthesized on fused-quartz glass substrate at room temperature by vacuum electron-beam coevaporation. Linear optical transmittance measurements reveal an indirect optical absorption edge with a blueshift as large as 1.6 eV due to the quantum confinement effects. The Z-scan method is used to study the third-order nonlinear absorption process of the synthesized samples, which clearly show a two-photon nonlinear process. Results also suggest that Ge nanocluster density or size is of great influence to the value of nonlinear absorption coefficient β.

Effect of B-site Al-doping on electric polarization in DyMnO3

We investigate the effect of Al-doping on the multiferroicity of DyMn1−xAlxO3. It is indicated that a slight doping (0.005≤x≤0.01) can significantly enhance the electric polarization which will be suppressed as x>0.03. The possible mechanism for the polarization enhancement is the rearrangement of the Mn spiral spin order upon the Al-doping. Our work demonstrates that the ferroelectricity of DyMnO3 is sensitive to the B-site nonmagnetic doping, allowing an unusual enhancement of the electric polarization.

Preparation of hafnium oxide thin film by electron beam evaporation of hafnium incorporating a post thermal process

Electron beam evaporation was employed to deposit hafnium on silicon (100) substrate, followed by a rapid thermal oxidation process to fabricate hafnium dioxide thin film. Hafnium was transformed to hafnium oxide above a oxidizing temperature of 500 °C. An interfacial layer of hafnium silicate was observed between HfO2 and silicon substrate. Oxidation temperature greatly affects interfacial quality and leakage current of the film.

Preparation of PZT on diamond by pulsed laser deposition with Al2O3 buffer layer

For the purpose of broad-bandwidth high frequency surface acoustic wave devices fabrication, we report on the successful preparation of Pb(Zr0.52Ti0.48)O-3 (PZT) films by pulsed laser deposition (PLD) process on (1 1 1)-oriented polycrystalline diamond substrates with aluminum oxide (Al2O3) as buffer layer. Al2O3 was deposited on diamond substrates by high-vacuum electron-beam evaporation method at 200 degreesC. Then PLD technique was used for PZT deposition. The chemical states of Al and O in Al2O3 were investigated by X-ray photoelectron spectroscopy. The surface morphology of Al2O3 and PZT films was studied by the atom force microscopy image. X-ray diffraction results showed that before annealing, 350 degreesC-prepared PZT was amorphous and 550 degreesC-prepared PZT was (2 2 2)-oriented pyrochlore phase PZT After rapid thermal annealing at 650 degreesC, (1 0 1)-oriented pure perovskite phase PZT could be obtained from the 350 degreesC-prepared PZT film

Interfacial stability between zirconium oxide thin films and silicon

We studied the interfacial properties of ZrO2 thin films deposited by ultra-high vacuum electron beam evaporation (UHV-EBE). Some samples were annealed in O2 ambient by rapid thermal annealing (RTA) at different temperatures ranging from 300 to 700 °C. X-ray photoelectron spectroscopy (XPS) of all films, whether annealed or not, revealed that the binding energies of Zr3d5/2 and Zr3d3/2 are 183.5 and 185.7 eV, respectively, which are the typical peak values of Zr4+. X-ray diffraction (XRD) results showed that the as-deposited film was amorphous, and it remained stable up to the annealing temperature of 600 °C. But when the temperature increased further attaining 700 °C, it began to crystallize. All the surfaces of the thin films were smooth and uniform. The typical RMS roughness ranged from 0.546 to 0.666 nm across an area of 50 × 50 µm. Steep and clear interfaces between zirconium oxide thin film and Si substrate were obtained both by spreading resistance profile (SRP) and cross-sectional transmission electron microscopy (XTEM). High quality of the interface without interfacial oxide was achieved when the annealing temperatures were kept under 600 °C, but when the temperature was raised to 700 °C, ∼ 1-nm thick oxide product was detected by XTEM. The component of the oxide product is not exactly known yet, but may be SiOx or ZrSixOy.

Deposition of high k ZrO/sub 2/ thin films by high vacuum electron beam evaporation at room temperature

Amorphous zirconium oxide (ZrO/sub 2/) films have been deposited on P type Si [100] substrates using High Vacuum Electron Beam Evaporation (HVEBE) at room temperature. The chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). The experimental results reveal that the dominating chemical state of zirconia thin films is fully oxidized state, Zr/sup 4+/, no matter whether annealed in oxygen. The structure information from X-ray Diffraction (XRD) shows that zirconia thin film deposited at room temperature by HVEBE was completely amorphous. Spreading Resistance Profile (SRP) indicates that ZrO/sub 2/ thin films annealed or not have excellent insulating property (with resistance of more than 10/sup 8/ /spl Omega/) and the thickness is 800 A. After thermal treatment at 600/spl deg/C in O/sub 2/ ambient, the RMS roughness changed a little to 13.8 A across an area of 1 /spl times/ 1 /spl mu/m/sup 2/, and that of the as-deposited film is 8.09 A.

Preparation of high quality amorphous Al/sub 2/O/sub 3/ thin film on silicon and its applications

Al/sub 2/O/sub 3/ thin films were deposited on silicon substrates by high-vacuum electron-beam evaporation method at 650/spl deg/C. Ferroelectric oxide (Pb(Zr/sub 0.52/Ti/sub 0.48/)O/sub 3/) (PZT) films were prepared on the Al/sub 2/O/sub 3/ buffer layer by pulsed laser deposition (PLD) method at 350/spl deg/C and rapid thermal annealing (RTA) at 650/spl deg/C. X-ray diffraction (XRD), X-ray photoelectron spectroscopes (XPS) and atomic force microscopy (AFM) results show that high quality amorphous Al/sub 2/O/sub 3/ could be obtained even at temperature as high as 650/spl deg/C. XRD result also indicates that highly [101]-oriented perovskite PZT can be obtained on the above mentioned Al/sub 2/O/sub 3/ buffer layer.