Thermal stability of nanocrystalline diamond films grown by biased enhanced microwave plasma chemical vapor deposition

The thermal stability of nanocrystalline diamond (NCD) films grown on mirror-polished silicon substrates by biased enhanced microwave plasma chemical vapor deposition was investigated. Different pieces of a NCD sample were annealed for 1 h in an ambient argon atmosphere at 200, 400, 600, and 800 degrees C. The structural and mechanical properties of as-grown and annealed samples were assessed. The surface roughness and high hardness of the samples remained fairly constant with annealing temperature.     

两段成长法改善微波电浆辅助化学气相沉积多晶金刚石之品质

以化学气相沉积法成长多晶金刚石薄膜时,薄膜的品质会受到成长时间、成长压力、反应气体比例、偏压与否及成核的机制等因素影响.研究采用微波电浆辅助化学气相沉积(MPECVD)法,以甲烷(CH4)和氢气(H2)作为反应气体原料,在P型(111)硅基板沉积多晶金刚石薄膜.典型沉积多晶金刚石薄膜的制程可分为四个阶段:抛蚀表面阶段、渗碳阶段、偏压增强成核(BEN)阶段及成长阶段.研究将成长阶段划分为两个阶段,第一阶段压力较低(成长Ⅰ阶段),第二阶段压力较高(成长Ⅱ阶段).结果表明:第一阶段可大大改善金刚石薄膜的品质,所获多晶金刚石薄膜的晶粒具有明确的颗粒边界、较低的碳化物或缺陷,电导率急剧降低,显现出本徵金刚石半绝缘的性质.可以认为金刚石薄膜品质的改善完全为低压成长所致.实验发现在成长Ⅰ阶段或成长Ⅱ阶段施加偏压时,只会降低多晶金刚石薄膜的品质.     

Advances in plasma-enhanced chemical vapor deposition of silicon films at low temperatures

The properties of silicon films prepared by plasma-enhanced chemical vapor deposition (PECVD) at low temperatures (<400 °C) are controlled by the physical and chemical processes that occur in the gas phase, at the top-most film surface, within the first several monolayers of the surface, and even well into the film bulk. Recent advances in understanding these processes have led to several new developments in silicon PECVD. The advances include: (i) novel concepts for depositing high-rate, device-quality silicon films, and (ii) deposition phase diagrams for optimizing silicon films for high-stability, high-performance devices. In situ and real time probes of the gas phase, the film surface, and its sub-surface have played key roles in these advances.     

Device-quality polycrystalline silicon films deposited at low process temperatures by hot-wire chemical vapor deposition

Device-grade undoped hydrogenated polycrystalline silicon thin films have been developed from a gas mixture of silane and hydrogen using a hot-wire chemical vapor deposition (HW-CVD) method, optimizing the deposition parameters. Proper design of the HW-CVD reactor helps to deposit a uniform quality of film over a large area (100 cm²) with a two filament configuration. Extensive studies have been made of the effects of hydrogen dilution (4–60), substrate temperature (180–400°C) and filament temperature (1500–1700°C) on the film growth. Atomic force micrographs give a quantitative estimate of roughness for these films. UV-visible ellipsometry analyses confirm their compactness and crystallinity while X-ray diffraction patterns allow for the determination of the crystallite sizes (up to 400 Å). Using a hydrogen dilution of 60, a substrate temperature of 300°C and a filament temperature of 1500°C, a dark conductivity of 2.5×10⁻⁵ S/cm and its activation energy of 0.45 eV have been obtained. For these films, the Hall mobility attains 10 cm²/V s. With these deposition parameters, the intrinsic layer of complete p–i–n HW-CVD solar cells has been realized. These cells, deposited on TCO coated Corning glass substrates, exhibit 1.8% conversion efficiency under 100 mW/cm² irradiation.     

Comparative study of the electrical properties of diamond films grown by microwave plasma assisted and hot-filament chemical vapor deposition

Schottky diodes were built on different polycrystalline diamond films grown by Microwave Plasma and Hot Filament Chemical Vapor Deposition and their electrical properties were studied. The barrier height increased with the diamond film quality and the corresponding ideality factor decreased. Even though the lower-quality HFCVD film displayed poor rectifying properties, it was found to be much less sensitive to variations in the operating conditions (air vs. vacuum). The activation energies of the films depend on morphological parameters, as preferable grain size or orientation. The bulk conduction also depends on the quality of the deposited films, changing from ohmic to trap-free or shallow trap SCLC and SCLC with an exponential distribution of traps. The hypothesis of using the electrical measurements as an indicator for film quality has been discussed.     

Characterization of MgZnO films grown by plasma enhanced metal-organic chemical vapor deposition

MgZnO (magnesium-zinc-oxide) films were grown on (11-20) sapphire substrates and Zn-polar ZnO substrates by plasma enhanced metal-organic chemical vapor deposition (PE-MOCVD) employing microwave-excited plasma. Structural, electrical and optical properties were investigated by X-ray diffraction, atomic force microscope, Hall, transmittance and photoluminescence measurement. The c-axis lattice constant decreases proportionally to an increase in the Mg content of Mg_xZn_1 − xO films. Therefore, this indicates that Mg atoms can be substituted in the Zn sites. Mg contents in films on ZnO substrates increase up to 0.11. In addition, Ga doped ZnO films were grown on (11-20) sapphire substrates. The resistivity of the films on (11-20) sapphire is controlled between 1.2 × 10^− 3 Ω cm to 1 Ω cm by changing the process conditions. The overall results indicate the promising potential of this PE-MOCVD method for related (Zn, Mg)O films formation because of the reactivity of the radicals, such as oxygen radicals (O?).     

Structure of diamond and diamond like carbon thin films grown by hot-filament chemical vapour deposition technique

Micro-crystalline diamond (MCD) and diamond like carbon (DLC) thin films were deposited on silicon (100) substrates by hot-filament CVD process using a mixture of CH₄ and H₂ gases at substrate temperature between 400–800°C. The microstructure of the films were studied by X-ray diffraction and scanning electron microscopy. The low temperature deposited films were found to have a mixture of amorphous and crystalline phases. At high temperatures (> 750°C) only crystalline diamond phase was obtained. Scanning electron micrographs showed faceted microcrystals of sizes up to 2μm with fairly uniform size distribution. The structure of DLC films was studied by spectroscopic ellipsometry technique. An estimate of the amount of carbon bonds existing insp ² andsp ³ form was obtained by a specially developed modelling technique. The typical values ofsp ³/sp ² ratio in our films are between 1·88–8·02. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Structural properties of phase-change InSbTe thin films grown at a low temperature by metalorganic chemical vapor deposition

The feasibility of new InSbTe (IST) chalcogenide materials at the deposition temperatures of 225 and 250 degrees C using metalorganic chemical vapor deposition (MOCVD) for phase-change random access memory (PRAM) applications was investigated. Samples grown at 225 degrees C consisted of the main InTe phase, including a small amount of Sb. On the other hand, samples grown at 250 degrees C included the crystalline phases of InSb and InSbTe. MOCVD-IST materials are powerful candidates for highly-integrated PRAM applications.     

直流热阴极CVD金刚石薄膜生长特性研究

为了获得高质量的金刚石薄膜,采用直流热阴极化学气相沉积系统分别在不同基片温度和不同碳源气体含量条件下生长金刚石薄膜,利用Raman光谱、SEM和XRD检测方法研究了基片温度和碳源气体含量对金刚石薄膜生长特性的影响.结果表明,金刚石薄膜与基片Mo之间有Mo2C的过渡层存在;1000℃的温度能够促进金刚石晶体的生长,抑制其他碳杂质的形成,CH4体积分数为2%适于快速生长高纯度的金刚石薄膜.     

The growth of Cu thin films by low pressure chemical vapor deposition

We study the growth of Cu films en route to the production of CuInSe₂ thin films as absorber layers in solar cells by a low pressure chemical vapor deposition technique. In order to obtain good quality films, the deposition conditions such as substrate, source temperatures, concentration ratio of Ar to H₂ have been optimized. The surface morphology and structural analysis of Cu films have been carried out. It is revealed that annealing resulted in a change in the properties of the films and also in the generation of other phases such as -Cu₅Si (cubic) and CuO (monoclinic). ©1999Kluwer Academic Publishers     

Preparation of nanosized silicon carbide powders by chemical vapor deposition at low temperatures

Liquid carbosilane was synthesized and analyzed by infrared (IR) and H-NMR (nuclear magnetic resonance) spectroscopy. Silicon carbide (SiC) powders were prepared by chemical vapor deposition (CVD) at 850°C and 900°C from liquid carbosilanes. The product powders were characterized by IR spectroscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Results show that liquid carbosilane synthesized was the mixture of several oligomers that had a Si-C backbone. The powders prepared at 850°C contain some organic segments, and those prepared at 900°C are pure nanosized SiC powders, which are partly crystallized, the size of which is about 50–70 nm. Translated from Journal of Functional Materials and Devices, 2006, 12(5): 447–450 (in Chinese)     

Effects of temperature on ZnO hybrids grown by metal-organic chemical vapor deposition

The growth of three-dimensional ZnO hybrid structures by metal-organic chemical vapor deposition was controlled through their growth pressure and temperature. Vertically aligned ZnO nanorods were grown on c-plane of sapphire substrate at 600 °C and 400 Torr. ZnO film was then formed in situ on the ZnO nanorods at 100, 600, and 700 °C and 10 Torr. High-resolution X-ray diffraction measurements showed that the ZnO film on the nanorods/sapphire grew epitaxially, and that the ZnO film/nanorods hybrid structures had well-ordered wurtzite structures. The hybrid ZnO structure was shown to be about 3–5 μm by field-emission scanning electron microscopy. The hybrid formed at 600 °C showed better crystalline quality those formed at 100 °C or 700 °C. These structures have potential applicability as nanobuilding blocks in nanodevices.     

Characteristics improvement of metalorganic chemical vapor deposition grown MgZnO films by MgO buffer layers

MgZnO films with a small quantity of Mg were grown on c-sapphire substrates coated with a thin MgO buffer layers by metalorganic chemical vapor deposition. The MgO buffer layer causes improvement in the structural, optical, and electrical properties of subsequently deposited MgZnO thin films, when compared to MgZnO films deposited without a buffer layer. The MgZnO films with a MgO buffer layer grown at 330 °C showed the best performance. Transmission electron microscopy revealed that the cubic phase MgO buffer layer promoted the epitaxial behavior of MgZnO, where the planar relationships of the wurtzite-MgZnO/cubic-MgO/sapphire heterostructures mainly were MgZnO(0001)//MgO(001)//sapphire(0001) and MgZnO(11?00)//MgO(110)//sapphire(112?0). It resulted in lower lattice mismatch between MgO and MgZnO by domain epitaxy of 2/1 and enhancement in preferred growth of the MgZnO films along the c-axis.     

Catalytic chemical vapor deposition of single-wall carbon nanotubes at low temperatures

We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350 degrees C by catalytic chemical vapor deposition from undiluted C2H2. NH3 or H2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.     

Depth dependence of structural quality in InN grown by metalorganic chemical vapor deposition

Rutherford backscattering and channeling is combined with X-ray diffraction to study the depth dependence of crystalline quality in InN layers grown by metalorganic chemical vapor deposition on sapphire substrate. The poorest crystalline quality in InN layer is produced at the intermediate region over 100 nm away from the InN/sapphire interface. With increasing layer thickness the crystalline quality improves to a certain degree dependent on the growth temperature. The InN sample grown at 450 °C is found to be more homogeneous than the sample grown at 550 °C. The difference in the defect profile is explained by the temperature-dependent growth modes. The inhomogeneity of structural quality and related properties such as carrier concentration and strain field is possibly the reason to observe a high energy wing in PL spectrum of the InN sample grown at 550 °C.     

Phase composition of mixed ZnS-EuS thin films grown by metal organic chemical vapor deposition

The phase composition of the mixed ZnS-EuS films deposited from volatile dithiocarbamates has been studied using differential dissolution technique (chemical method of the phase analysis) and electron microscopy. Phase composition was found to depend on the Eu content in the films, that in turn depends on a flow density ratio of the Eu and Zn volatile precursors. A single-phase solid solution, Zn_0.998Eu_≤0.002S, was observed only for films with Eu content≤1 mol%, other films were found to be two-phase. For films with the Eu content between 2 and 16% and above 80%, impurity phases, EuS and ZnS, respectively, were detected by differential dissolution technique. They evolved as low-sized sulfide precipitates encapsulated in an organic coat. No impurity phases in the films of the same Eu content were noticed by X-ray technique and Raman spectroscopy. For the films with the Eu content between 16 and 80%, sulfide phases, ZnS and EuS, were found to be free from any organic coat, and structural methods as with differential dissolution technique were also capable of observing the phases. Conditions are given to prepare Eu doped ZnS films of good quality by MOCVD technique.     

Morphologies of carbon micro-coils grown by chemical vapor deposition

The carbon micro-coils were obtained by the Ni-catalyzed pyrolysis of acetylene. The carbon micro-coils with various coiling morphology: regular double coils, coils built up by circular or flat fibers, super helix coils, single coils, etc. can be observed. The carbon coils with various coil diameters and coil pitches were obtained by controlling reaction conditions, such as reaction temperature, source gas flow rate of sulfur-impurity, acetylene or hydrogen.     

Comprehensive study of graphene grown by chemical vapor deposition

Graphene was grown on Cu foil by chemical vapor deposition with CH₄ as carbon source, and then was transferred onto various substrates for device applications. The structural and optical properties of graphene were investigated, comprehensively. Raman spectra indicate as-grown and transferred graphene films are homogenous monolayer graphene. Optical microscopy and scanning electron microscopy images reveal wrinkle-free and smooth surface of transferred graphene, confirming the high quality of graphene. In addition, the transferred graphene on glass exhibits excellent transmittances in the visible region (89.3 % at ~500 nm). Therefore, the results present the controllable approaches to achieve as-grown and transferred high quality graphene for the fabrication of multiple nanoelectronic devices.     

Transparent conducting indium oxide thin films grown by low-temperature metal organic chemical vapor deposition

We have grown indium oxide thin films on silicon substrates at low temperature by metal organic chemical vapor deposition. Polycrystalline film growth could only be obtained at temperatures below 400 °C. Above 400 °C, metallic indium deposition dominated. We have investigated the effect of substrate temperature and reactor pressure on the film growth and structural properties in the range of 250-350 °C and 5 ^? 10³-4 ^? 10⁴ Pa. The film grown at 300 °C exhibited a resistivity of about 3.6 × 10^− 3 Ω cm and a maximal optical transmittance of more than 95% in the visible range. The film showed an optical band gap of about 3.6 eV.     

Effect of water vapor on the growth of aluminum oxide films by low pressure chemical vapor deposition

Low pressure chemical vapor deposition of aluminum oxide films from aluminum acetylacetonate and water vapor has been investigated. Water vapor played an important role in the film growth kinetics, film purity, and the surface morphology of the grown films. High water vapor pressures produced ligand-free pure Al₂O₃ films with a smooth surface even at a substrate temperature of 230 °C.