Textured tetragonal ZrO2 film grown on (100) silicon surface by DLI metal-organic chemical vapor deposition

Zirconia (ZrO2) thin films with micronic layer thickness are deposited on Si(100) substrates by MOCVD in a cold wall reactor using direct injection (DLI-CVD) process with Zr2(OiPr)6(thd)2 precursor diluted in cyclohexane. The effects of experimental parameters such as substrate's temperature, injection frequency, oxygen partial pressure in the reactive chamber and deposition duration of the process are investigated in order to produce a strongly textured tetragonal ZrO2 film. The films crystalline structure and crystallite size (several nm) are identified by Grazing incidence X-ray diffraction (GIXRD); the microstructure and morphology are observed with the use of FEG-SEM. GIXRD patterns showed the predominance of nano-crystallized tetragonal phase (or cubic) in the films. Pole figures have been analysed for both {111}(t-c) and {200}(t-c) planes in order to evaluate the relationship binding the preferential crystallographic orientation to the column-like growth structure. Besides, the internal stresses levels (with the use of sin2 psi method) within zirconia layers varied from a compressive to a tensile state depending on the experimental deposition conditions and are related to phase orientation and/or transformation into monoclinic one. It is demonstrated that high temperature, low pressure and low deposition time enhanced the tetragonal phase quality that became highly (200)t textured.     

Hot-wire chemical vapor deposition of epitaxial film crystal silicon for photovoltaics

We have demonstrated that hot-wire chemical vapor deposition (HWCVD) is an excellent technique to produce high-quality epitaxial silicon at high rates, at substrate temperatures from 620 to 800 °C. Fast, scalable, inexpensive epitaxy of high-quality crystalline Si (c-Si) in this temperature range is a key element in creating cost-competitive film Si PV devices on crystalline seed layers on inexpensive substrates such as display glass and metal foil. We have improved both the quality and rate of our HWCVD Si epitaxy in this display-glass-compatible T range. We understand factors critical to high-quality epitaxial growth and obtain dislocation densities down to 6 × 10⁴ cm⁻² by techniques that reduce the surface oxygen contamination at the moment growth is initiated. We have also developed and validated a model of the HWCVD silicon growth rate, based on fundamentals of reaction chemistry and ideal gas physics. This model enables us to predict growth rates and calculate the sticking coefficient of the Si radicals contributing to film formation between 300 and 800 °C. We obtain efficiencies up to 6.7% with a 2.5-micron absorber layer grown on heavily-doped ‘dead’ Si wafers although these cells still lack hydrogenation and light trapping. Open-circuit voltages up to 0.57 V are obtained on 2-μm cells. Efficient film crystal silicon photovoltaics will require dislocation spacing more than 6 times the cell thickness, or else effective H passivation of the dislocations.     

Gas phase particle formation and elimination on Si (100) in low temperature reduced pressure chemical vapor deposition silicon-based epitaxial layers

Gas phase particle formation and elimination in silicon epitaxial layers grown on Si (100) substrates using reduced pressure chemical vapor deposition at low temperatures (< 600 °C) are investigated. High-order silane precursors (Si_nH_2n + 2; n = 3, n > 3) are useful for high growth rate epitaxy at low temperature. However, particulates are observed on the surface of the epitaxial layers grown with high-order silanes. These particulates are attributed to gas phase particles. As atomically smooth epitaxial films are desired, the elimination of gas phase particles is required. Cyclical deposition and etch process and/or low pressure deposition enables atomically smooth SiCP epitaxial films with a high-order silane.     

Polymer layers by initiated chemical vapor deposition for thin film gas barrier encapsulation

A combination of SiN_x and polymer layers, in our case poly(glycidyl methacrylate) (PGMA) is very suitable as a permeation barrier layer on sensitive electronic devices. Our experiments thus far concentrate on increasing the stability and deposition rate of the polymer layers. To reach the thermal stability needed for the deposition of SiN_x on PGMA by HWCVD, the PGMA chain length must be large. PGMA with a very high molecular weight (M_W) (78,000 Da, ~ 548 monomers) was deposited at a high deposition rate (> 60 nm/min). To mimic the reactive atomic H ambient during SiN_x deposition conditions during HWCVD, the polymer layers were exposed to an atomic hydrogen environment for 0 to 550 s. Surprisingly, the most important factor for stability under these conditions was the filament temperature which was used during PGMA deposition, rather than the expected parameters such as M_W or surface roughness. Using lower filament temperatures for PGMA deposition, the layers were much more stable in atomic H ambient.     

Growth and characterization of undoped ZnSe epitaxial layers obtained by organometallic chemical vapour deposition

Epitaxial ZnSe layers have been grown on GaAs substrates by the metal alkyl hydride technique. First we describe the design of the reactor geometry necessary in order to obtain constant thickness layers. Then the influence of the experimental conditions (gas flows, vapour composition, temperature, substrate orientation) on the growth kinetics and on the crystalline and luminescent properties is described. The results obtained from this work allow us to determine the growth conditions, the different growth processes involved and the origin of contamination. After parameter optimization this method provides low temperature undoped ZnSe epilayers with the same luminescent properties as high purity bulk samples.     

X-ray photoelectron spectroscopy (XPS) investigation of the surface film on magnesium powders

Magnesium (Mg) and its alloys are attractive for use in automotive and aerospace applications because of their low density and good mechanical properties. However, difficulty in forming magnesium and the limited number of available commercial alloys limit their use. Powder metallurgy may be a suitable solution for forming near-net-shape parts. However, sintering pure magnesium presents difficulties due to surface film that forms on the magnesium powder particles. The present work investigates the composition of the surface film that forms on the surface of pure magnesium powders exposed to atmospheric conditions and on pure magnesium powders after compaction under uniaxial pressing at a pressure of 500 MPa and sintering under argon at 600 °C for 40 minutes. Initially, focused ion beam microscopy was utilized to determine the thickness of the surface layer of the magnesium powder and found it to be ~10 nm. The X-ray photoelectron analysis of the green magnesium sample prior to sintering confirmed the presence of MgO, MgCO(3)·3H(2)O, and Mg(OH)(2) in the surface layer of the powder with a core of pure magnesium. The outer portion of the surface layer was found to contain MgCO(3)·3H(2)O and Mg(OH)(2), while the inner portion of the layer is primarily MgO. After sintering, the MgCO(3)·3H(2)O was found to be almost completely absent, and the amount of Mg(OH)(2) was also decreased significantly. This is postulated to occur by decomposition of the compounds to MgO and gases during the high temperature of sintering. An increase in the MgO content after sintering supports this theory.     

Growth and characterization of germanium epitaxial film on silicon (001) using reduced pressure chemical vapor deposition

High quality germanium (Ge) epitaxial film is grown directly on silicon (001) substrate using a “three-step growth” approach in a reduced pressure chemical vapor deposition system. The growth steps consist of sequential low temperature (LT) at 400 °C, intermediate temperature ramp (LT-HT) of ~ 6.5 °C/min and high temperature (HT) at 600 °C. This is followed by post-growth anneal in hydrogen at temperature ranging from 680 to 825 °C. Analytical characterizations have shown that the Ge epitaxial film of thickness ~ 1 μm experiences thermally induced tensile strain of 0.20% with a threading dislocation density of < 10⁷ cm^− 2 under optical microscope and root mean square roughness of ~ 0.9 nm. Further analysis has shown that the annealing time at high temperature has an impact on the surface morphology of the Ge epitaxial film. Further reduction in the RMS roughness can be achieved either through chemical mechanical polishing or to insert an annealing step between the LT-HT ramp and HT steps.     

Ge组分渐变的Si1-x-yGexCy薄膜的制备

用化学气相淀积方法在Si（100）衬底上外延生长了Ge组分最高约0．40的组分渐变的Si1-x-yGexCy合金薄膜,研究了生长温度等工艺参数的影响．结果表明,生长温度和C2H4分压的提高均导致薄膜中碳组分的增加和合金薄膜晶格常数的减小,这表明外延薄膜中的C主要以替位式存在．C掺入量的变化可有效地调节薄膜的禁带宽度,而提高生长温度有助于改善Si1-x-yGexCy薄膜的的晶体质量．组分渐变的Si1-x-yGexCy合金薄膜包括由因衬底中Si原子扩散至表面与GeH4．C2H4反应而生成的Ni1-x-yGexCy外延层和由Ni1-x-yGexCy外延层中Ge原子向衬底方向扩散而形成的Ni1-xGex层．     

Nanostructuring Si-C alloys by plasma enhanced chemical vapor deposition: An ellipsometry and Raman spectroscopy investigation

Silicon nanocrystals embedded in a dielectric matrix are of considerable interest for Si-based optoelectronics and the third generation photovoltaics. This work discusses Si nanocrystals embedded in silicon-carbon, Si_1 − xC_x, thin films prepared by plasma-enhanced chemical vapor deposition (PECVD) using a non-conventional fluoride-based precursor mixture, i.e., SiF₄-CH₄-H₂-He plasmas. It is shown that the SiF₄/H₂ ratio and the He dilution are important parameters to control the volume fraction and the size of nc-Si, and the carbon content of the a-Si_1 − xC_x matrix. Films nanostructure and optical properties are studied by spectroscopic ellipsometry and Raman spectroscopy. The correlation existing between plasma processes and the film nanostructure and resulting optical properties is discussed.     

An investigation of epitaxial films by means of high energy electron diffraction: II. A study of film morphology

In the present work film morphology was studied by an electron diffraction method. The electron microscopy replica method seems to be insufficient to give unambiguous information concerning film morphology and the growth process, but a combination of diffraction data and electron microscope observations gives much more complete information. We applied these methods to investigations of Ge epitaxial films on GaAs and Si substrates at different stages of growth (at thicknesses of 20 Å upwards).     

The vapour phase deposition of thick epitaxial (100) ZnS layers on elemental and compound substrates in H2 gas flow

Journal of Materials Science - An investigation of the epitaxial growth of (100) ZnS on GaAs, GaP, Si, Ge and sapphire substrates in H2 gas flow is described. The objective of the work was to...     

The influence of ordered surface point defect arrays on the epitaxial deposition of gold upon (100) surfaces of sodium chloride

The effect of an ordered array of sodium ion vacancies (incorporated into a (100) surface of sodium chloride) upon the epitaxial temperature associated with gold being deposited onto that (100) surface has been investigated. A dramatic reduction in the epitaxial temperature has been observed, and single-crystal correctly oriented gold films have been achieved at - 30 °C upon those areas of the sodium chloride surface containing the point defects.     

Oxide formation on the silicon (111) surface studied by Auger electron spectroscopy and by low energy electron loss spectroscopy

Core electron and valence electron excitation spectra measured using low energy electron loss spectroscopy in combination with Auger electron spectroscopy were used to study oxide formation on clean crystalline silicon. The chemical bonds formed in the various oxidation stages are described by localized molecular states. SiO double bonds, Si—O bonds of the type found in SiO₄ tetrahedra, Si—Si bonds and broken Si—O bonds were detected.     

Nickel carbide: Its formation and characterization by transmission electron diffraction,Auger electron spectroscopy and electron spectroscopy for chemical analysis

Nickel carbide (NiC₃) films are formed by the carburization of nickel films in CO at 350°C. The presence of Ni₃C is demonstrated by transmission electron diffraction. The carbon Auger electron signal of Ni₃C is identical with the carbon Auger spectra attributed to Ni₃C by previous authors. The position of the C 1s electron spectroscopy for chemical analysis peak is within 1 eV of the C 1s peak produced by graphite. The grain size of polycrystalline Ni₃C is significantly larger than the grain size of the nickel film from which it is grown.     

Combinatorial initiated chemical vapor deposition (iCVD) for polymer thin film discovery

Initiated chemical vapor deposition (iCVD) is a technique used to synthesize polymer thin films and coatings from the vapor phase in situ on solid substrates via free-radical mechanisms. It is a solventless, low-temperature process capable of forming very thin conformal layers on complex architectures. By implementing a combinatorial approach that examines five initiation temperatures simultaneously, we have realized at least a five-fold increase in efficiency. The combinatorial films were compared to a series of blanket films deposited over the same conditions to ensure the combinatorial system provided the same information. Direct synthesis from the vapor phase allows for in situ control of film morphology, molecular weight and crosslinking, and the combinatorial system decreases the time required to find the relationship between these interrelated properties. Some coatings were tested for antimicrobial performance against E. coli and B. subtilis.     

Bandgap determination of P(VDF-TrFE) copolymer film by electron energy loss spectroscopy

The ferroelectric β of poly(vinylidene fluoride trifluoroethylene), P(VDF-TrFE) is confirmed for 100 nm thickness spin coated copolymer film. The homogeneous coverage of the copolymer film is investigated by the help of X-ray photoelectron spectroscopy (XPS). Most importantly, the existing bandgap in the crystalline phase of the copolymer is determined directly from the electron energy loss spectroscopy (EELS).