wei Shi

Composition dependence of interface control and optimization on the performance of an HfTiON gate dielectric metal-oxide-semiconductor capacitor

Composition dependence of interface control, band alignment and electrical properties of HfTiON/Si grown by sputtering has been studied by spectroscopy ellipsometry (SE), x-ray photoelectron spectroscopy (XPS) and electrical measurement. Analysis from XPS has confirmed that the interfacial layer consisting of silicate and SiOx is formed unavoidably, irrespective of composition ratio. Meanwhile, reduction in band gap and asymmetric band alignment has been detected for HfTiON films with the increase in Ti composition. To meet the requirements of high-k dielectrics with the barrier height of over 1 eV, the incorporation composition ratio needs to be carefully optimized. As a result, improved C–V characteristics and reduced leakage current have been achieved from HfTiON gate dielectric MOS capacitors with optimized composition ratio of Hf:Ti = 1:1, which can be attributed to the reduction in oxygen-related traps and the obtained near-symmetric band alignment relative to Si.

Study of near white light emission for ZnO thin films grown on silicon substrates

ZnO thin films at growth time of 6, 8, 10 and 12 h were prepared by hydrothermal approach. The microstructure, surface morphology and photoluminescence properties were investigated by x-ray diffraction, field-emission scanning electron microscope and fluorescence spectrometer. The results reveal that all the thin films have hexagonal wurzite structure and preferential orientation along the c-axis. The density of nanorods increases first and then decreases with the increase of growth time. The photoluminescence spectra consist of sharp near band-edge, broad visible and near-infrared emissions. The chromaticity coordinates and color rendering indices of ZnO thin film at growth time of 10 h are x = 0.3537, y = 0.3744 and 90, respectively. The mechanisms of the green, yellow, orange-red, red and near-infrared emissions were discussed in detail.

Metal-organic chemical vapor deposition of aluminium oxynitride from propylamine–dimethylaluminium hydride and oxygen: growth mode dependence and performance optimization

AlOxNy thin films have been successfully obtained by new metal-organic chemical vapor deposition (MOCVD) chemistry using propylamine–dimethylaluminium hydride (DMAH) mixture and O2 as precursor and oxidant, respectively. Attention has been paid to investigate the MOCVD behavior of this new precursor as a function of the process parameters in the MOCVD of AlOxNy films. A new growth mode based on atomic layer deposition (ALD) mechanism has been carried out to optimize the MOCVD process. Compared to the normal mode, suppressed interface growth and improved electrical properties have been observed for ALD-mode-derived samples. Electrical measurements based on post-deposition annealing (PDA) and forming gas annealing (FGA) processed samples have indicated that better electrical performance are achieved in FGA-derived AlOxNy films. Based on analysis and observations, it can be concluded that ALD-mode-derived AlOxNy films grown by ALD MOCVD chemistry demonstrate potential application as high-k candidates in future nano-devices taking advantage of the improved physical and electrical performance.

The improved photo-induced hydrophilicity of ZnO by adjusting the solution concentration

The microstructure, surface topography and wetting properties of zinc oxide (ZnO) thin films, which were grown at different concentrations of zinc nitrate hexahydrate, were measured by x-ray diffractometry, scanning electron microscopy and water contact angle apparatus. It is revealed that at concentrations larger than 0.01 mol l−1, one peak corresponds to the (111) direction of the cubic phase of ZnO, except for six peaks of the hexagonal phase of ZnO, was observed. As the concentration increases, the average diameter and density of the ZnO nanorods increase but the area proportion of the nonpolar planes in the outermost surface increase first, then decrease. All the ZnO thin films exhibit hydrophobic behavior. After 120 min of ultraviolet irradiation, the wettability of the ZnO surfaces change from hydrophobicity to hydrophilicity. The photo-induced change of the water contact angle increases first then decreases with the increase of concentration. The differences of photo-induced hydrophilicity may be determined by the transition of the wetting model, the area proportion of the nonpolar planes and the surface roughness.

Structure and photoluminescence study of silicon based two-dimensional Si2Te3 nanostructures

As an emerging silicon-based two-dimensional (2D) material, vertical and horizontal Si2Te3 nanoplates on various substrates have been deposited by chemical vapor deposition. Structure, composition, and optical properties of these nanostructures are investigated by electron microscopy, x-ray photoelectron emission, energy dispersive x-ray spectroscopy, and temperature dependent photoluminescence. Band gap emissions of Si2Te3 nanoplates containing four noticeable emission peaks, i.e., free exciton, acceptor-bound exciton (A0X), and phonon replicas of A0X, are observed at temperatures below 90 K. The temperature dependent emission intensity of A0X indicates there are two quenching channels, which are associated with thermal quenching and thermal dissociations of A0X to free excitons. Two defect emissions are observed at measurement temperatures from 10 to 300 K, and their peak energies decrease by following the band gap change at low temperature range but increase at high temperature range as the temperature...

Influence of Solution Concentrations on Surface Morphology and Wettability of ZnO Thin Films

ZnO thin films were grown on silicon substrates using a hydrothermal method. The XRD patterns show that all of the peaks can be attributed to the wurtzite structures of ZnO. The TC value of (002) plane and average crystal size increase first and then decrease with the increase of solution concentration. SEM and AFM results show that many dense hexagonal cylinder particles have been observed on the surface of the thin films, which grown at 0.08 and 0.10 mol/L. The surface roughness of the thin films deposited at 0.06, 0.08, 0.10, and 0.12 mol/L are 24.5, 38.3, 32.0, and 39.4 nm, respectively. Surface wettability results show that the preferential orientation along c-axis and surface roughness contribute significantly to the hydrophobicity. The reversible switching between hydrophobicity and hydrophilicity is related to the synergy of the transition of wetting model, surface crystal structure, and surface roughness.

Enhanced photoelectrochemical properties of nanocrystalline TiO 2 electrode by surface sensitization with Cu x O quantum dots

Nanoporous anatase TiO2 films were fabricated by a screen-printing method, and CuxO quantum dots (QDs) were deposited on the TiO2 films through successive ionic layer adsorption and reaction (SILAR). The amount of CuxO QDs on the TiO2 films are controlled by changing the number of SILAR cycles. The morphology, microstructure, optical, and photoelectrochemical properties of different CuxO sensitized TiO2 films (CuxO/TiO2) were investigated in detail. The nanoporous TiO2 film offers a large surface area for anchoring QDs. QD deposited samples exhibited a significant improvement in photoelectrochemical performance than the bare of TiO2. CuxO/TiO2, prepared with 7 SILAR cycles, showed the best photoelectrochemical properties, where the photocurrent density was enhanced to 500.01 μA/cm2 compared with 168.88 μA/cm2 of bare TiO2 under visible light. These results indicate that the designed CuxO/TiO2 structure possesses superior charge separation efficiency and photoelectrochemical properties.

Effect of oxygen partial pressure and transparent substrates on the structural and optical properties of ZnO thin films and their performance in energy harvesters

Zinc oxide (ZnO) thin films were deposited onto different substrates — tin-doped indium oxide (ITO)/glass, ITO/polyethylene naphthalate (PEN), ITO/polyethylene terephthalate (PET) — by the radio-frequency (RF) magnetron sputtering method. The effect of various O2/(Ar+O2) gas flow ratios (0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) was studied in detail. ZnO layers deposited onto ITO/PEN and ITO/PET substrates exhibited a stronger c-axis preferred orientation along the (0002) direction compared to ZnO deposited onto ITO/glass. The transmittance spectra of ZnO films showed that the maximum transmittances of ZnO films deposited onto ITO/glass, ITO/PEN, and ITO/PET substrates were 89.2%, 65.0%, and 77.8%, respectively. Scanning electron microscopy (SEM) images of the film surfaces indicated that the grain was uniform. The cross-sectional SEM images showed that the ZnO films were columnar structures whose c-axis was perpendicular to the film surface. The test results for a fabricated ZnO thin film based energy harvester showed that its output voltage increased with increasing acceleration of external vibration.

EFFECT OF MOLYBDENUM DOPING AND ANNEALING ON PHOTOLUMINESCENCE OF SPUTTERING-DERIVED ZINC OXIDE FILMS

The molybdenum-doped ZnO (MZO) films were deposited on quartz substrates by radio frequency magnetron sputtering. All films have a polycrystalline hexagonal wurtzite structure. Mo doping influences the grain size of the MZO films and leads to a compressive stress in the films. The valence of Mo in the MZO films is hexavalence. Mo doping enhances the emissions at 380 and 412 nm. Annealing significantly influences the photoluminescence (PL) spectra of the MZO films. The PL spectral intensity of the annealed films is much higher than that of the unannealed films. The emissions at 400 and 525 nm enhanced dramatically with the rising of annealing temperature while the emissions at 380 and 412 nm became weak or disappeared. Mo doping is beneficial for the enhancement of the emissions at 400 and 525 nm of the annealed MZO films. The origins of these emissions were discussed in detail.