Search

This paper reports that by using the hydrofluoric acid (HF) as the acid catalyst, F doped nanoporous low-k SiO2 thin films have been prepared by means of sol-gel method. The characterization of atomic force microscopy and Fourier transform infrared spectroscopy demonstrates that the HF catalyzed films are more hydrophobic. The N2 adsorption/desorption experiments show that the suited introduction of HF increases the porosity and decreases the pore size distribution (about 10 nm) in the films. The above results indicate that the hydrofluoric acid is the more suitable acid catalyst than the hydrochloric one for preparing nanoporous ultra low-k SiO2 thin films.

Zinc oxide (ZnO) thin films were deposited on (100) Si substrates by sol-gel technique. Zinc acetate was used as the precursor material. The effect of different annealing atmospheres and annealing temperatures on composition, structural and optical properties of ZnO thin films was investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy and photoluminescence (PL), respectively. At an annealing temperature of 400°C in N2 for 2 h, dried gel films were propitious to undergo structural relaxation and grow ZnO grains. ZnO thin film annealed at 400°C in N2 for 2 h exhibited the optimal structure and PL property, and the grain size and the lattice constants of the film were calculated (41.6 nm, a = 3.253 A and c = 5.210 A). Moreover, a green emission around 495 nm was observed in the PL spectra owing to the oxygen vacancies located at the surface of ZnO grains. With increasing annealing temperature, both the amount of the grown ZnO and the specific surface area of the grains decrease, which jointly weaken the green emission.

Tb-doped Zinc oxide (ZnO:Tb) films were prepared by RF reactive magnetron sputtering of a Zn target with some Tb-chips attached. The results show that the appropriate Tb ions incorporated into ZnO films can improve the structural and electrical properties of ZnO films. Photoluminescence (PL) measurements show that the characteristic emission lines correspond to the intra-4fn-shell transitions in Tb3+ ions at room temperature. Under the optimal conditions, the ZnO:Tb films were prepared with the lowest resistivity (ρ) of 9.34 × 10−4Ωcm, transmittance over 80% at the visible region and the strong blue emission.

Three-dimensional SiO2 photonic crystals (PhCs) are fabricated on quartz substrates by the vertical deposition method. Scanning electron microscopy measurement reveals that the samples exhibit an ordered close-packed arrangement of SiO2 spheres. It is found that the position of the [111] photonic band gap (PBG) shifts to a long wavelength (red shift) with increasing sphere size. Gap broadening effects are observed due to the presence of defects in the samples. Moreover, the optical properties of the PBG are very sensitive to the annealing temperature. Our results indicate that the optical properties of the PBG can be easily tuned in the visible region by appropriate experimental parameters, which will be useful for practical applications of PhC optical devices.

The as-deposited Au/Ti/p-diamond contacts prepared by rf sputtering are ohmic. The ohmic characteristics of the contacts are improved after annealing. As for the as-deposited and annealed contacts, the specific contact resistivities of 2.886 ? 10-3 and 2.040 ? 10-4 ??cm2 are obtained, respectively. The x-ray photoelectron spectroscopy analysis indicates that the titanium carbide formation occurs at the interface between titanium and the diamond substrate in the as-deposited state, and no TiO2 is observed.

ZnO:Ni films with different doping concentrations （0—7at.%） have been deposited by radio frequency magnetron sputtering. The results of x-ray diffraction, including θ-2θ mode and rocking curve mode, indicate that the film doped with 5at.% Ni shows an excellent preferred growth along c-axis orientation. The （002） diffraction peak shifts to a larger angle, which implies that Ni atoms are incorporated into the ZnO lattice. For ZnO:Ni films with good transparency in the visible range, the optical band gap evaluated by the fitting method decreases linearly from 3.272 to 3.253 eV with increasing Ni concentration. Undoped ZnO film exhibits a green emission peak and Ni-doped ZnO films mainly emit a blue photoluminescence centred at 430 nm, we believe that they might be ascribed to crystal defects of oxygen vacancies and interstitial zinc, respectively.

ZnO∶In thin films with thickness varying in the 210—240nm range were prepared on quartz substrates by sol_gel spin_coating technique. The structural properties of these thin films (In/Zn=0, 1, 2, 3 and 5at%) were studied by grazing incidence X_ray diffraction, conventional X_ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and photoluminescence. It is found that the ZnO∶In thin films are composed of the unstressed bulk layer packed up by large grains with (002) plane and the surface layer by small grains with (002) and (103) planes, and a proper In doping concentration can improve structural properties of ZnO thin films. The analytic results were further proved by grazing incidence X_ray diffraction at different incidence angles (α=1, 2, 3 and 5°).

Y-doped Al2O3 dielectric films have been fabricated by reactive radio frequency co-sputtering method. Grazing angle incidence x-ray diffraction results show that the as-deposited and annealed films are amorphous. High resolution scanning electron microscope and atomic force microscope have been applied to observe the cross-section and the surface morphology of the thin films. The electric C-V and I-V characteristics were measured at high and variable frequency, respectively. It was found that the dielectric constant k of the films increases remarkably (from 8.14 to 11.8) with increasing Y-doping concentration. The Y—O bond is stronger than Al—O due to the obvious difference in electro-negativity between the two bond members, which enhanced the ionic polarization in the thin films leading to an increase of the dielectric constant. It was supposed that the presence of Y ions changed the structure and atomic coordination of Al2O3. The films were very smooth which meet the requirements of the device.

The SiC:Tb films were deposited on porous silicon substrate by rfsputtering. The samples prepared were annealed in N2 atmosphere at different temperatures, and Fourier transform infrared has been used to characterize the structure of them. We observed a strong photoluminescence(PL) spectrum at room temperature in the ultraviolet(UV) and visible regions. We found that the UV emission has obvious changed and a slight blue shift was observed with the change of annealing temperature. The UV and visible PLs were attributed to oxygen deficit center(ODC) and Tb3+ respectively.

Zinc oxide films doped with various contents of copper were deposited on silicon (111) substrates by rf reactive sputtering. The photoluminescent(PL) spectra of the ZnO films were measuered at room temperature. Results showed that each of the samples had a blue band at about 435nm (2.85eV) and the intensities of these blue bands were changed with the variation of content and sputtering power. It was observed that there is a stronger blue bi-peak when the power reaches 150W and the copper content is equal to 2.5%, and there is a stronger blue peak at 437?nm when the power was 100?W and copper content is 1.5% on the PL spectra of ZnO films, the latter had a good c axis orientation. We have investigated the PL properties for various Cu-doped contents and different sputtering powers, and the mechanism of blue emission was also discussed in this paper.

Low dielectric constant thin film of nanoporous silica synthesized by sol-gel was deposited on Si(100) substrate by spin coating. By detecting —CH3 substituted for —OH species, which can avoid the destruction of network, surface modification was identified by Fourier transform infrared spectroscope. The hole size was about 70-80 nm observed from scanning electron microscope. By adjusting the pH value of the sol, we found that the gel time increased with the decrease o f the pH value of the sol. When heating the modified film at different temperatu res (60-400 ℃)， we can obtain the lowest dielectric constant 2.05 at 300 ℃ .

Highly oriented polycrystalline ZnO films have been prepared by rf actively sputtering technique. We have investigated the structural and optical properties of ZnO films. x-ray diffraction was employed to analyze the influence of the post-treatment on the properties of ZnO thin films. The grain size increases with annealing temperature. The shift of the diffraction peak position from its normal powder value was observed. The photoluminescence (PL) spectra of these samples consist of one emission peak centred at 2.9eV.The intensities of PL peaks decrease with increasing annealing temperature. We propose that the emission comes from the interstitial Zn.

Si1-x-yGexCy ternary alloy semiconductor films were prepared on Si(100) substrates by C ion implanting SiGe films and subsequest solid phase epitaxy (SPE). Two-step annealing technique was employed in the SPE processing. The properties of the alloy films were determined using Rutherford backscattering spectroscopy (RBS), Fourier transform infrared spectroscopy (MR) and High-resolution x-ray diffraction (HRXRD) measurements. It is shown that C atoms are located at substitutional sites and the incorporation of C relieves the compressive strain in the SiGe layer.

Si-containing silicon oxide (SSO) films and Ge-containing silicon oxide (GSO) films were deposited on p-type Si substrates using the RF magnetron sputtering technique with a Si-SiO2 and a Ge-SiO2 composite target, respectively. These films were annealed in a N2 ambient at temperatures from 300 to 1100℃. Using high resolution transmission electron microscopy,nanometer Si particles and nanometer Ge particles were observed in the SSO and GSO films,respectively,after annealing at 900 or 1100℃. All the PL spectra from the two types of films annealed at various temperatures have similar shapes with peak positions around 580nm (～2.1eV). It is indicated that light emission originates from luminescence centers in Si oxide films. The experimental results have been explained reasonably.

The thermal stability of a-Si:H/a-Ge:H superlattices was studied using LR and XRD spec tra. It was found that the crystallization temperature of superlattices with small layer thickness is higher than that of bulk a-Ge:H. Results are discussed preliminarily.

Thermally induced metastable defects in reactive sputtered a-SiGe:H films are studied by conductivity σ(T) and heterojunction capacitance-voltage (C-V) measure ments.

The paper presents the light‐induced effect of n‐ and p‐type GD a‐SixC1−x: H films by the use of MOSFET structure and coplanar contacts. It was found that, after prolonged light illumination, the gap state density increases and the photoconductance shows a slight decrease. The dark conductance of B state is related to EA (the A state activation energy).