Monto Carlo simulation of the behaviour of electrons during electron—assisted chemical vapour deposition of diamond

The behaviour of electrons during electron-assisted chemical vapour deposition of diamond is investigated using Monte Carlo simulation. The electron energy distribution and velocity distribution are obtained over a wide range of reduced field E/N (the ratio of the electric field to gas molecule density) from 100 to 2000 in units of 1Td=10^-17Vcm². Their effects on the diamond growth are also discussed. The main results obtained are as follows. (1) The velocity profile is asymmetric for the component parallel to the field. The velocity distribution has a peak shift in the field direction. Most electrons possess non-zero velocity parallel to the substrate. (2) The number of atomic H is a function of E/N. (3) High-quality diamond can be obtained under the condition of E/N from 50 to 800Td due to sufficient atomic H and electron bombardment.     

Fast Growth of Polycrystalline Film in SiCl4／H2 Plasma

We report the discovery, of fast growth of polycrystalline silicon films under low temperature of 200-300℃ from SiCl4/H2 mixture gases by plasma enhanced chemical vapour deposition technique. The deposition rate strongly depends not only on the rf power and the flow ratio of H2/SiCl4, but also on the substrate temperature, while the crystalline fraction is mainly affected by both the rf power and the flow ratio of H2/SiCl4. The high film-growth rate is due to the enhancement of the gas-phase reaction in SICI4/‘H2 plasma. By gleans of adjusting the matchingrelation between the flow ratio of H2/SiCl4 and rf power, and optimizing the substrate temperasure, we obtain the potycrystalline silicon films deposited at a higher deposition rate over 3.5A/s, with a crystalline fraction of 75% and an average crystallite size of 400-500nm in diameter.     

Low-Temperature Growth of Polycrystalline silicon Films by SiCl4／H2 rf Plasma Enhanced Chemical Vapour Deposition

Polycrystalline silicon film was directly fabricated at 200℃ by the conventional plasma enhanced chemical vapour deposition method from SiCl4 with H2 dilution. The crystallization depends strongly on the deposition power.The maximum crystMlinity and the crystalline grain size are over 80% and 200—50Onm, respectively. The results of energy dispersive spectroscopy and infrared spectroscopy measurements demonstrate that the film is mostly composed of silicon, without impurities such as Cl, N, C and bonded H. It is suggested that the crystallization at such a low temperature originates from the effects of chlorine, i.e., in-situ chemical, etching, in-situ chemical cleaning, and the detachment of bonded H.     

First nucleation steps during deposition of SiO2 thin films by plasma enhanced chemical vapour deposition

The initial nucleation stages during deposition of SiO₂ by remote plasma enhanced chemical vapour deposition (PECVD) have been monitored by XPS inelastic peak shape analysis. Experiments have been carried out on two substrates, a flat ZrO₂ thin film and a silicon wafer with a native silicon oxide layer on its surface. For the two substrates it is found that PECVD SiO₂ grows in the form of islands. When the SiO₂ particles reach heights close to 10 nm they coalesce and cover completely the substrate surface. The particle formation mechanism has been confirmed by TEM observation of the particles grown on silicon substrates. The kinetic Monte Carlo simulation of the nucleation and growth of the SiO₂ particles has shown that formation of islands is favoured under PECVD conditions because the plasma species may reach the substrate surface according to off-perpendicular directions. The average energy of these species is the main parameter used to describe their angular distribution function, while the reactivity of the surface is another key parameter used in the simulations.     

Exclusion zone surrounding silicon nanoclusters formed by rapid thermal chemical vapour deposition on SiO2

We present results of an experimental investigation on the nearest-neighbour distance of silicon nanoclusters obtained by chemical vapour deposition of silane on silicon oxide substrates. Structural characterization has been performed by means of energy filtered transmission electron microscopy, which allowed us to observe dot sizes down to 0.5 nm in radius. We have found that silicon nanodots after deposition are separated by a minimum distance of about 4 nm. This effect has also been observed on samples deposited in the same conditions on substrates which have been subjected to different chemical treatments. The phenomenon is attributed to the existence of a capture zone, within which new deposited Si monomers preferentially contribute to the growth of a previously nucleated seed rather than aggregate to form a new nucleus. As a confirmation of this hypothesis, the average dot radius has been observed to be proportional to the capture region size, thus indicating a scaling behaviour for this process. Moreover when the inter-dot distance distribution is scaled to its average value, it collapses into a universal curve.     

Fabrication of 160-nm T-gate metamorphic AlInAs/GaInAs HEMTs on GaAs substrates by metal organic chemical vapour deposition

The fabrication and performance of 160-nm gate-length metamorphic AlInAs/GaInAs high electron mobility tran-sistors (mHEMTs) grown on GaAs substrate by metal organic chemical vapour deposition (MOCVD) are reported. By using a novel combined optical and e-beam photolithography technology, submicron mHEMTs devices have been achieved. The devices exhibit good DC and RF performance. The maximum current density was 817 mA/mm and the maximum transconductance was 828 mS/mm. The non-alloyed Ohmic contact resistance Rc was as low as 0.02 Ω- mm. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) were 146 GHz and 189 GHz, respectively. This device has the highest fT yet reported for a 160-nm gate-length HEMTs grown by MOCVD. The output conductance is 28.9 mS/mm, which results in a large voltage gain of 28.6. Also, an input capacitance to gate-drain feedback capacitance ratio, Cgs/Cgd, of 4.3 is obtained in the device.     

不同初始温度下H2/O2混合物等离子体的演化

本文对不同初始温度下,H₂/O₂混合物等离子体中主要粒子随时间发展的演化规律进行了数值模拟,得到了放电后等离子体中主要带电粒子和中性粒子密度随时间的变化规律.计算结果表明,H₂/O₂混合物等离子体中主要活性粒子密度随时间的增加减小,化学反应达到平衡所需的时间随初始温度升高逐渐减少.     

Electron field emission characteristics of nano-catkin carbon films deposited by electron cyclotron resonance microwave plasma chemical vapour deposition

This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface morphology and the structure of the fabricated films were characterized by using scanning electron microscopes and Raman spectroscopy, respectively. The stable field emission properties with a low threshold field of 5V/μm corresponding to a current density of about 1μA/cm^2 and a current density of 3.2mA/cm^2 at an electric field of 10V/μm were obtained from the carbon film deposited at CH4 concentration of 8%. The mechanism that the threshold field decreased with the increase of the CH4 concentration and the high emission current appeared at the high CH4 concentration was explained by using the Fowler-Nordheim theory.     

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence （PL） and lasing properties of InAs/GaAs quantum dots （QDs） with different growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the low growth rate sample shows a greater blueshift of PL peak wavelength. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blueshift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.     

甲烷在不同分子筛中吸附的理论对比研究

使用巨正则蒙特卡罗方法研究了CH₄分子在MOR和MFI分子筛中的物理吸附行为, 主要对比研究了这两种分子筛对CH₄分子在不同温度和压强下的物理吸附量、等量吸附热、 分子筛和CH₄以及CH₄和CH₄分子之间的相互作用能等物理量. 研究结果表明:在所有的温度和压力下, MOR分子筛对CH₄分子的吸附性能均优于相应的MFI分子筛, 这表明它是一种比MFI吸附性能更优异的吸附剂材料.从CH₄在这两种分子筛中的等量吸附热随吸附量的变化关系,分子筛和CH₄以及CH₄和CH₄之间的相互作用能分布曲线等角度出发分析了二者有不同吸附行为的原因.     

Elucidating surface properties of dry-etched ZnO using H2/CH4 and H2/CH4/Ar plasma

This paper reports a study of reactive ion etching (RIE) of n-ZnO in H₂/CH₄ and H₂/CH₄/Ar gas mixtures. Variables in the experiment were gas flow ratios, radio-frequency (rf) plasma power, and total pressure. Structural and electrical parameters of the etched surfaces and films were determined. Both the highest surface roughness and highest etching rate of ZnO films were obtained with a maximum rf power of 300 W, but at different gas flow ratios and working pressures. These results were expected because increasing the rf power increased the bond-breaking efficiency of ZnO. The highest degree of surface roughness was a result of pure physical etching by H₂ gas without mixed CH₄ gas. The highest etching rate was obtained from physical etching of H₂/Ar species associated with chemical reaction of CH₄ species. Additionally, the H₂/CH₄/Ar plasma treatment drastically decreased the specific contact and sheet resistance of the ZnO films. These results indicated that etching the ZnO film had roughened the surface and reduced its resistivity to ohmic contact, supporting the application of a roughened transparent contact layer (TCL) in light-emitting diodes (LEDs).     

SiC epitaxial layers grown by chemical vapour deposition and the fabrication of Schottky barrier diodes

This paper presents the results of unintentionally doped 4H-SiC epilayers grown on n-type Si-faced 4H-SiC substrates with 8° off-axis toward the [11\overline 2 0] direction by low pressure horizontal hot-wall chemical vapour deposition. Growth temperature and pressure are 1580~°C and 10⁴~Pa, respectively. Good surface morphology of the sample is observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize epitaxial layer thickness and the structural quality of the films respectively. The carrier concentration in the unintentional 4H-SiC homoepitaxial layer is about 6.4×10¹⁴~cm^-3 obtained by c--V measurements. Schottky barrier diodes (SBDs) are fabricated on the epitaxial wafer in order to verify the quality of the wafer and to obtain information about the correlation between background impurity and electrical properties of the devices. Ni and Ti/4H-SiC Schottky barrier diodes with very good performances were obtained and their ideality factors are 1.10 and 1.05 respectively.